Add Support for Jackson 3 (#742)

This change adds Jackson 3 support and aligns package naming in the existing Jackson 2 module.

Specific changes:
* Deprecated classes for removal in `io.modelcontextprotocol.json.jackson`/`io.modelcontextprotocol.json.schema.jackson`
* Copied the above to `io.modelcontextprotocol.json.jackson2`/`io.modelcontextprotocol.json.schema.jackson2` in non-deprecated form.
* Added tests for the default McpJsonMapper and JsonSchemaValidator

mcp-core/pom.xml

@@ -80,7 +80,7 @@
 		<dependency>
 			<groupId>com.fasterxml.jackson.core</groupId>
 			<artifactId>jackson-annotations</artifactId>
-			<version>${jackson.version}</version>
+			<version>${jackson-annotations.version}</version>
 		</dependency>
 
 		<dependency>
@@ -100,7 +100,7 @@
 		<!-- Test dependencies -->
         <dependency>
             <groupId>io.modelcontextprotocol.sdk</groupId>
-            <artifactId>mcp-json-jackson2</artifactId>
+            <artifactId>mcp-json-jackson3</artifactId>
             <version>0.18.0-SNAPSHOT</version>
             <scope>test</scope>
         </dependency>

mcp-core/src/test/java/io/modelcontextprotocol/spec/McpSchemaTests.java

@@ -10,6 +10,7 @@ import static net.javacrumbs.jsonunit.assertj.JsonAssertions.json;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 
+import java.io.IOException;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashMap;
@@ -18,7 +19,7 @@ import java.util.Map;
 
 import org.junit.jupiter.api.Test;
 
-import com.fasterxml.jackson.databind.exc.InvalidTypeIdException;
+import tools.jackson.databind.exc.InvalidTypeIdException;
 
 import io.modelcontextprotocol.spec.McpSchema.TextResourceContents;
 import net.javacrumbs.jsonunit.core.Option;
@@ -58,7 +59,9 @@ public class McpSchemaTests {
 	void testContentDeserializationWrongType() throws Exception {
 
 		assertThatThrownBy(() -> JSON_MAPPER.readValue("""
-				{"type":"WRONG","text":"XXX"}""", McpSchema.TextContent.class))
+				{"type":"WRONG","text":"XXX"}""", McpSchema.TextContent.class)).isInstanceOf(IOException.class)
+			.hasMessage("Failed to read value")
+			.cause()
 			.isInstanceOf(InvalidTypeIdException.class)
 			.hasMessageContaining(
 					"Could not resolve type id 'WRONG' as a subtype of `io.modelcontextprotocol.spec.McpSchema$TextContent`: known type ids = [audio, image, resource, resource_link, text]");

mcp-json-jackson2/pom.xml

@@ -11,7 +11,7 @@
 	<artifactId>mcp-json-jackson2</artifactId>
 	<packaging>jar</packaging>
 	<name>Java MCP SDK JSON Jackson</name>
-	<description>Java MCP SDK JSON implementation based on Jackson</description>
+	<description>Java MCP SDK JSON implementation based on Jackson 2</description>
 	<url>https://github.com/modelcontextprotocol/java-sdk</url>
 	<scm>
 		<url>https://github.com/modelcontextprotocol/java-sdk</url>
@@ -42,12 +42,12 @@
         <dependency>
             <groupId>com.fasterxml.jackson.core</groupId>
             <artifactId>jackson-databind</artifactId>
-            <version>${jackson.version}</version>
+            <version>${jackson2.version}</version>
         </dependency>
         <dependency>
             <groupId>com.networknt</groupId>
             <artifactId>json-schema-validator</artifactId>
-            <version>${json-schema-validator.version}</version>
+            <version>${json-schema-validator-jackson2.version}</version>
         </dependency>
 
 		<dependency>

mcp-json-jackson2/src/main/java/io/modelcontextprotocol/json/jackson/JacksonMcpJsonMapper.java

@@ -14,7 +14,12 @@ import java.io.IOException;
 /**
  * Jackson-based implementation of JsonMapper. Wraps a Jackson ObjectMapper but keeps the
  * SDK decoupled from Jackson at the API level.
+ *
+ * @deprecated since 18.0.0, use
+ * {@link io.modelcontextprotocol.json.jackson2.JacksonMcpJsonMapper} instead. Will be
+ * removed in 19.0.0
  */
+@Deprecated(forRemoval = true, since = "18.0.0")
 public final class JacksonMcpJsonMapper implements McpJsonMapper {
 
 	private final ObjectMapper objectMapper;

mcp-json-jackson2/src/main/java/io/modelcontextprotocol/json/jackson/JacksonMcpJsonMapperSupplier.java

@@ -13,7 +13,12 @@ import io.modelcontextprotocol.json.McpJsonMapperSupplier;
  * <p>
  * This implementation provides a {@link McpJsonMapper} backed by a Jackson
  * {@link com.fasterxml.jackson.databind.ObjectMapper}.
+ *
+ * @deprecated since 18.0.0, use
+ * {@link io.modelcontextprotocol.json.jackson2.JacksonMcpJsonMapperSupplier} instead.
+ * Will be removed in 19.0.0.
  */
+@Deprecated(forRemoval = true, since = "18.0.0")
 public class JacksonMcpJsonMapperSupplier implements McpJsonMapperSupplier {
 
 	/**

mcp-json-jackson2/src/main/java/io/modelcontextprotocol/json/jackson2/JacksonMcpJsonMapper.java

@@ -0,0 +1,88 @@
+/*
+ * Copyright 2026 - 2026 the original author or authors.
+ */
+
+package io.modelcontextprotocol.json.jackson2;
+
+import java.io.IOException;
+
+import com.fasterxml.jackson.databind.JavaType;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+import io.modelcontextprotocol.json.McpJsonMapper;
+import io.modelcontextprotocol.json.TypeRef;
+
+/**
+ * Jackson-based implementation of JsonMapper. Wraps a Jackson ObjectMapper but keeps the
+ * SDK decoupled from Jackson at the API level.
+ */
+public final class JacksonMcpJsonMapper implements McpJsonMapper {
+
+	private final ObjectMapper objectMapper;
+
+	/**
+	 * Constructs a new JacksonMcpJsonMapper instance with the given ObjectMapper.
+	 * @param objectMapper the ObjectMapper to be used for JSON serialization and
+	 * deserialization. Must not be null.
+	 * @throws IllegalArgumentException if the provided ObjectMapper is null.
+	 */
+	public JacksonMcpJsonMapper(ObjectMapper objectMapper) {
+		if (objectMapper == null) {
+			throw new IllegalArgumentException("ObjectMapper must not be null");
+		}
+		this.objectMapper = objectMapper;
+	}
+
+	/**
+	 * Returns the underlying Jackson {@link ObjectMapper} used for JSON serialization and
+	 * deserialization.
+	 * @return the ObjectMapper instance
+	 */
+	public ObjectMapper getObjectMapper() {
+		return objectMapper;
+	}
+
+	@Override
+	public <T> T readValue(String content, Class<T> type) throws IOException {
+		return objectMapper.readValue(content, type);
+	}
+
+	@Override
+	public <T> T readValue(byte[] content, Class<T> type) throws IOException {
+		return objectMapper.readValue(content, type);
+	}
+
+	@Override
+	public <T> T readValue(String content, TypeRef<T> type) throws IOException {
+		JavaType javaType = objectMapper.getTypeFactory().constructType(type.getType());
+		return objectMapper.readValue(content, javaType);
+	}
+
+	@Override
+	public <T> T readValue(byte[] content, TypeRef<T> type) throws IOException {
+		JavaType javaType = objectMapper.getTypeFactory().constructType(type.getType());
+		return objectMapper.readValue(content, javaType);
+	}
+
+	@Override
+	public <T> T convertValue(Object fromValue, Class<T> type) {
+		return objectMapper.convertValue(fromValue, type);
+	}
+
+	@Override
+	public <T> T convertValue(Object fromValue, TypeRef<T> type) {
+		JavaType javaType = objectMapper.getTypeFactory().constructType(type.getType());
+		return objectMapper.convertValue(fromValue, javaType);
+	}
+
+	@Override
+	public String writeValueAsString(Object value) throws IOException {
+		return objectMapper.writeValueAsString(value);
+	}
+
+	@Override
+	public byte[] writeValueAsBytes(Object value) throws IOException {
+		return objectMapper.writeValueAsBytes(value);
+	}
+
+}

mcp-json-jackson2/src/main/java/io/modelcontextprotocol/json/jackson2/JacksonMcpJsonMapperSupplier.java

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2026 - 2026 the original author or authors.
+ */
+
+package io.modelcontextprotocol.json.jackson2;
+
+import io.modelcontextprotocol.json.McpJsonMapper;
+import io.modelcontextprotocol.json.McpJsonMapperSupplier;
+
+/**
+ * A supplier of {@link McpJsonMapper} instances that uses the Jackson library for JSON
+ * serialization and deserialization.
+ * <p>
+ * This implementation provides a {@link McpJsonMapper} backed by a Jackson
+ * {@link com.fasterxml.jackson.databind.ObjectMapper}.
+ */
+public class JacksonMcpJsonMapperSupplier implements McpJsonMapperSupplier {
+
+	/**
+	 * Returns a new instance of {@link McpJsonMapper} that uses the Jackson library for
+	 * JSON serialization and deserialization.
+	 * <p>
+	 * The returned {@link McpJsonMapper} is backed by a new instance of
+	 * {@link com.fasterxml.jackson.databind.ObjectMapper}.
+	 * @return a new {@link McpJsonMapper} instance
+	 */
+	@Override
+	public McpJsonMapper get() {
+		return new JacksonMcpJsonMapper(new com.fasterxml.jackson.databind.ObjectMapper());
+	}
+
+}

mcp-json-jackson2/src/main/java/io/modelcontextprotocol/json/schema/jackson/DefaultJsonSchemaValidator.java

@@ -24,7 +24,11 @@ import org.slf4j.LoggerFactory;
  * NetworkNT JSON Schema Validator library for validation.
  *
  * @author Christian Tzolov
+ * @deprecated since 18.0.0, use
+ * {@link io.modelcontextprotocol.json.schema.jackson2.DefaultJsonSchemaValidator}
+ * instead. Will be removed in 19.0.0.
  */
+@Deprecated(forRemoval = true, since = "18.0.0")
 public class DefaultJsonSchemaValidator implements JsonSchemaValidator {
 
 	private static final Logger logger = LoggerFactory.getLogger(DefaultJsonSchemaValidator.class);

mcp-json-jackson2/src/main/java/io/modelcontextprotocol/json/schema/jackson/JacksonJsonSchemaValidatorSupplier.java

@@ -13,6 +13,9 @@ import io.modelcontextprotocol.json.schema.JsonSchemaValidatorSupplier;
  *
  * @see JsonSchemaValidatorSupplier
  * @see JsonSchemaValidator
+ * @deprecated since 18.0.0, use
+ * {@link io.modelcontextprotocol.json.schema.jackson2.JacksonJsonSchemaValidatorSupplier}
+ * instead. Will be removed in 19.0.0.
  */
 public class JacksonJsonSchemaValidatorSupplier implements JsonSchemaValidatorSupplier {
 

mcp-json-jackson2/src/main/java/io/modelcontextprotocol/json/schema/jackson2/DefaultJsonSchemaValidator.java

@@ -0,0 +1,163 @@
+/*
+ * Copyright 2026-2026 the original author or authors.
+ */
+package io.modelcontextprotocol.json.schema.jackson2;
+
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.networknt.schema.Error;
+import com.networknt.schema.Schema;
+import com.networknt.schema.SchemaRegistry;
+import com.networknt.schema.dialect.Dialects;
+
+import io.modelcontextprotocol.json.schema.JsonSchemaValidator;
+
+/**
+ * Default implementation of the {@link JsonSchemaValidator} interface. This class
+ * provides methods to validate structured content against a JSON schema. It uses the
+ * NetworkNT JSON Schema Validator library for validation.
+ *
+ * @author Christian Tzolov
+ */
+public class DefaultJsonSchemaValidator implements JsonSchemaValidator {
+
+	private static final Logger logger = LoggerFactory.getLogger(DefaultJsonSchemaValidator.class);
+
+	private final ObjectMapper objectMapper;
+
+	private final SchemaRegistry schemaFactory;
+
+	// TODO: Implement a strategy to purge the cache (TTL, size limit, etc.)
+	private final ConcurrentHashMap<String, Schema> schemaCache;
+
+	public DefaultJsonSchemaValidator() {
+		this(new ObjectMapper());
+	}
+
+	public DefaultJsonSchemaValidator(ObjectMapper objectMapper) {
+		this.objectMapper = objectMapper;
+		this.schemaFactory = SchemaRegistry.withDialect(Dialects.getDraft202012());
+		this.schemaCache = new ConcurrentHashMap<>();
+	}
+
+	@Override
+	public ValidationResponse validate(Map<String, Object> schema, Object structuredContent) {
+
+		if (schema == null) {
+			throw new IllegalArgumentException("Schema must not be null");
+		}
+		if (structuredContent == null) {
+			throw new IllegalArgumentException("Structured content must not be null");
+		}
+
+		try {
+
+			JsonNode jsonStructuredOutput = (structuredContent instanceof String)
+					? this.objectMapper.readTree((String) structuredContent)
+					: this.objectMapper.valueToTree(structuredContent);
+
+			List<Error> validationResult = this.getOrCreateJsonSchema(schema).validate(jsonStructuredOutput);
+
+			// Check if validation passed
+			if (!validationResult.isEmpty()) {
+				return ValidationResponse
+					.asInvalid("Validation failed: structuredContent does not match tool outputSchema. "
+							+ "Validation errors: " + validationResult);
+			}
+
+			return ValidationResponse.asValid(jsonStructuredOutput.toString());
+
+		}
+		catch (JsonProcessingException e) {
+			logger.error("Failed to validate CallToolResult: Error parsing schema: {}", e);
+			return ValidationResponse.asInvalid("Error parsing tool JSON Schema: " + e.getMessage());
+		}
+		catch (Exception e) {
+			logger.error("Failed to validate CallToolResult: Unexpected error: {}", e);
+			return ValidationResponse.asInvalid("Unexpected validation error: " + e.getMessage());
+		}
+	}
+
+	/**
+	 * Gets a cached Schema or creates and caches a new one.
+	 * @param schema the schema map to convert
+	 * @return the compiled Schema
+	 * @throws JsonProcessingException if schema processing fails
+	 */
+	private Schema getOrCreateJsonSchema(Map<String, Object> schema) throws JsonProcessingException {
+		// Generate cache key based on schema content
+		String cacheKey = this.generateCacheKey(schema);
+
+		// Try to get from cache first
+		Schema cachedSchema = this.schemaCache.get(cacheKey);
+		if (cachedSchema != null) {
+			return cachedSchema;
+		}
+
+		// Create new schema if not in cache
+		Schema newSchema = this.createJsonSchema(schema);
+
+		// Cache the schema
+		Schema existingSchema = this.schemaCache.putIfAbsent(cacheKey, newSchema);
+		return existingSchema != null ? existingSchema : newSchema;
+	}
+
+	/**
+	 * Creates a new Schema from the given schema map.
+	 * @param schema the schema map
+	 * @return the compiled Schema
+	 * @throws JsonProcessingException if schema processing fails
+	 */
+	private Schema createJsonSchema(Map<String, Object> schema) throws JsonProcessingException {
+		// Convert schema map directly to JsonNode (more efficient than string
+		// serialization)
+		JsonNode schemaNode = this.objectMapper.valueToTree(schema);
+
+		// Handle case where ObjectMapper might return null (e.g., in mocked scenarios)
+		if (schemaNode == null) {
+			throw new JsonProcessingException("Failed to convert schema to JsonNode") {
+			};
+		}
+
+		return this.schemaFactory.getSchema(schemaNode);
+	}
+
+	/**
+	 * Generates a cache key for the given schema map.
+	 * @param schema the schema map
+	 * @return a cache key string
+	 */
+	protected String generateCacheKey(Map<String, Object> schema) {
+		if (schema.containsKey("$id")) {
+			// Use the (optional) "$id" field as the cache key if present
+			return "" + schema.get("$id");
+		}
+		// Fall back to schema's hash code as a simple cache key
+		// For more sophisticated caching, could use content-based hashing
+		return String.valueOf(schema.hashCode());
+	}
+
+	/**
+	 * Clears the schema cache. Useful for testing or memory management.
+	 */
+	public void clearCache() {
+		this.schemaCache.clear();
+	}
+
+	/**
+	 * Returns the current size of the schema cache.
+	 * @return the number of cached schemas
+	 */
+	public int getCacheSize() {
+		return this.schemaCache.size();
+	}
+
+}

mcp-json-jackson2/src/main/java/io/modelcontextprotocol/json/schema/jackson2/JacksonJsonSchemaValidatorSupplier.java

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2026 - 2026 the original author or authors.
+ */
+
+package io.modelcontextprotocol.json.schema.jackson2;
+
+import io.modelcontextprotocol.json.schema.JsonSchemaValidator;
+import io.modelcontextprotocol.json.schema.JsonSchemaValidatorSupplier;
+
+/**
+ * A concrete implementation of {@link JsonSchemaValidatorSupplier} that provides a
+ * {@link JsonSchemaValidator} instance based on the Jackson library.
+ *
+ * @see JsonSchemaValidatorSupplier
+ * @see JsonSchemaValidator
+ */
+public class JacksonJsonSchemaValidatorSupplier implements JsonSchemaValidatorSupplier {
+
+	/**
+	 * Returns a new instance of {@link JsonSchemaValidator} that uses the Jackson library
+	 * for JSON schema validation.
+	 * @return A {@link JsonSchemaValidator} instance.
+	 */
+	@Override
+	public JsonSchemaValidator get() {
+		return new DefaultJsonSchemaValidator();
+	}
+
+}

mcp-json-jackson2/src/main/resources/META-INF/services/io.modelcontextprotocol.json.McpJsonMapperSupplier

@@ -1 +1 @@
-io.modelcontextprotocol.json.jackson.JacksonMcpJsonMapperSupplier
+io.modelcontextprotocol.json.jackson2.JacksonMcpJsonMapperSupplier

mcp-json-jackson2/src/main/resources/META-INF/services/io.modelcontextprotocol.json.schema.JsonSchemaValidatorSupplier

@@ -1 +1 @@
-io.modelcontextprotocol.json.schema.jackson.JacksonJsonSchemaValidatorSupplier
+io.modelcontextprotocol.json.schema.jackson2.JacksonJsonSchemaValidatorSupplier

mcp-json-jackson2/src/test/java/io/modelcontextprotocol/json/McpJsonMapperTest.java

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2026-2026 the original author or authors.
+ */
+
+package io.modelcontextprotocol.json;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+import io.modelcontextprotocol.json.jackson2.JacksonMcpJsonMapper;
+
+class McpJsonMapperTest {
+
+	@Test
+	void shouldUseJackson2Mapper() {
+		assertThat(McpJsonMapper.getDefault()).isInstanceOf(JacksonMcpJsonMapper.class);
+	}
+
+}

mcp-json-jackson2/src/test/java/io/modelcontextprotocol/json/jackson/DefaultJsonSchemaValidatorTests.java

@@ -0,0 +1,809 @@
+/*
+ * Copyright 2024-2024 the original author or authors.
+ */
+
+package io.modelcontextprotocol.json.jackson;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.when;
+
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Stream;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+
+import com.fasterxml.jackson.core.type.TypeReference;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+import io.modelcontextprotocol.json.schema.JsonSchemaValidator.ValidationResponse;
+import io.modelcontextprotocol.json.schema.jackson.DefaultJsonSchemaValidator;
+
+/**
+ * Tests for {@link DefaultJsonSchemaValidator}.
+ *
+ * @author Christian Tzolov
+ */
+@Deprecated(forRemoval = true)
+class DefaultJsonSchemaValidatorTests {
+
+	private DefaultJsonSchemaValidator validator;
+
+	private ObjectMapper objectMapper;
+
+	@Mock
+	private ObjectMapper mockObjectMapper;
+
+	@BeforeEach
+	void setUp() {
+		MockitoAnnotations.openMocks(this);
+		validator = new DefaultJsonSchemaValidator();
+		objectMapper = new ObjectMapper();
+	}
+
+	/**
+	 * Utility method to convert JSON string to Map<String, Object>
+	 */
+	private Map<String, Object> toMap(String json) {
+		try {
+			return objectMapper.readValue(json, new TypeReference<Map<String, Object>>() {
+			});
+		}
+		catch (Exception e) {
+			throw new RuntimeException("Failed to parse JSON: " + json, e);
+		}
+	}
+
+	private List<Map<String, Object>> toListMap(String json) {
+		try {
+			return objectMapper.readValue(json, new TypeReference<List<Map<String, Object>>>() {
+			});
+		}
+		catch (Exception e) {
+			throw new RuntimeException("Failed to parse JSON: " + json, e);
+		}
+	}
+
+	@Test
+	void testDefaultConstructor() {
+		DefaultJsonSchemaValidator defaultValidator = new DefaultJsonSchemaValidator();
+
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"test": {"type": "string"}
+					}
+				}
+				""";
+		String contentJson = """
+				{
+					"test": "value"
+				}
+				""";
+
+		ValidationResponse response = defaultValidator.validate(toMap(schemaJson), toMap(contentJson));
+		assertTrue(response.valid());
+	}
+
+	@Test
+	void testConstructorWithObjectMapper() {
+		ObjectMapper customMapper = new ObjectMapper();
+		DefaultJsonSchemaValidator customValidator = new DefaultJsonSchemaValidator(customMapper);
+
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"test": {"type": "string"}
+					}
+				}
+				""";
+		String contentJson = """
+				{
+					"test": "value"
+				}
+				""";
+
+		ValidationResponse response = customValidator.validate(toMap(schemaJson), toMap(contentJson));
+		assertTrue(response.valid());
+	}
+
+	@Test
+	void testValidateWithValidStringSchema() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"name": {"type": "string"},
+						"age": {"type": "integer"}
+					},
+					"required": ["name", "age"]
+				}
+				""";
+
+		String contentJson = """
+				{
+					"name": "John Doe",
+					"age": 30
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+		assertNotNull(response.jsonStructuredOutput());
+	}
+
+	@Test
+	void testValidateWithValidNumberSchema() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"price": {"type": "number", "minimum": 0},
+						"quantity": {"type": "integer", "minimum": 1}
+					},
+					"required": ["price", "quantity"]
+				}
+				""";
+
+		String contentJson = """
+				{
+					"price": 19.99,
+					"quantity": 5
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+	}
+
+	@Test
+	void testValidateWithValidArraySchema() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"items": {
+							"type": "array",
+							"items": {"type": "string"}
+						}
+					},
+					"required": ["items"]
+				}
+				""";
+
+		String contentJson = """
+				{
+					"items": ["apple", "banana", "cherry"]
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+	}
+
+	@Test
+	void testValidateWithValidArraySchemaTopLevelArray() {
+		String schemaJson = """
+				{
+					"$schema" : "https://json-schema.org/draft/2020-12/schema",
+					"type" : "array",
+					"items" : {
+						"type" : "object",
+						"properties" : {
+						"city" : {
+							"type" : "string"
+						},
+						"summary" : {
+							"type" : "string"
+						},
+						"temperatureC" : {
+							"type" : "number",
+							"format" : "float"
+						}
+						},
+						"required" : [ "city", "summary", "temperatureC" ]
+					},
+					"additionalProperties" : false
+				}
+					""";
+
+		String contentJson = """
+				[
+					{
+						"city": "London",
+						"summary": "Generally mild with frequent rainfall. Winters are cool and damp, summers are warm but rarely hot. Cloudy conditions are common throughout the year.",
+						"temperatureC": 11.3
+					},
+					{
+						"city": "New York",
+						"summary": "Four distinct seasons with hot and humid summers, cold winters with snow, and mild springs and autumns. Precipitation is fairly evenly distributed throughout the year.",
+						"temperatureC": 12.8
+					},
+					{
+						"city": "San Francisco",
+						"summary": "Mild year-round with a distinctive Mediterranean climate. Famous for summer fog, mild winters, and little temperature variation throughout the year. Very little rainfall in summer months.",
+						"temperatureC": 14.6
+					},
+					{
+						"city": "Tokyo",
+						"summary": "Humid subtropical climate with hot, wet summers and mild winters. Experiences a rainy season in early summer and occasional typhoons in late summer to early autumn.",
+						"temperatureC": 15.4
+					}
+				]
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+
+		// Validate as JSON string
+		ValidationResponse response = validator.validate(schema, contentJson);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+
+		List<Map<String, Object>> structuredContent = toListMap(contentJson);
+
+		// Validate as List<Map<String, Object>>
+		response = validator.validate(schema, structuredContent);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+	}
+
+	@Test
+	void testValidateWithInvalidTypeSchema() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"name": {"type": "string"},
+						"age": {"type": "integer"}
+					},
+					"required": ["name", "age"]
+				}
+				""";
+
+		String contentJson = """
+				{
+					"name": "John Doe",
+					"age": "thirty"
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertFalse(response.valid());
+		assertNotNull(response.errorMessage());
+		assertTrue(response.errorMessage().contains("Validation failed"));
+		assertTrue(response.errorMessage().contains("structuredContent does not match tool outputSchema"));
+	}
+
+	@Test
+	void testValidateWithMissingRequiredField() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"name": {"type": "string"},
+						"age": {"type": "integer"}
+					},
+					"required": ["name", "age"]
+				}
+				""";
+
+		String contentJson = """
+				{
+					"name": "John Doe"
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertFalse(response.valid());
+		assertNotNull(response.errorMessage());
+		assertTrue(response.errorMessage().contains("Validation failed"));
+	}
+
+	@Test
+	void testValidateWithAdditionalPropertiesNotAllowed() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"name": {"type": "string"}
+					},
+					"required": ["name"],
+					"additionalProperties": false
+				}
+				""";
+
+		String contentJson = """
+				{
+					"name": "John Doe",
+					"extraField": "should not be allowed"
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertFalse(response.valid());
+		assertNotNull(response.errorMessage());
+		assertTrue(response.errorMessage().contains("Validation failed"));
+	}
+
+	@Test
+	void testValidateWithAdditionalPropertiesExplicitlyAllowed() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"name": {"type": "string"}
+					},
+					"required": ["name"],
+					"additionalProperties": true
+				}
+				""";
+
+		String contentJson = """
+				{
+					"name": "John Doe",
+					"extraField": "should be allowed"
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+	}
+
+	@Test
+	void testValidateWithDefaultAdditionalProperties() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"name": {"type": "string"}
+					},
+					"required": ["name"],
+					"additionalProperties": true
+				}
+				""";
+
+		String contentJson = """
+				{
+					"name": "John Doe",
+					"extraField": "should be allowed"
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+	}
+
+	@Test
+	void testValidateWithAdditionalPropertiesExplicitlyDisallowed() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"name": {"type": "string"}
+					},
+					"required": ["name"],
+					"additionalProperties": false
+				}
+				""";
+
+		String contentJson = """
+				{
+					"name": "John Doe",
+					"extraField": "should not be allowed"
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertFalse(response.valid());
+		assertNotNull(response.errorMessage());
+		assertTrue(response.errorMessage().contains("Validation failed"));
+	}
+
+	@Test
+	void testValidateWithEmptySchema() {
+		String schemaJson = """
+				{
+					"additionalProperties": true
+				}
+				""";
+
+		String contentJson = """
+				{
+					"anything": "goes"
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+	}
+
+	@Test
+	void testValidateWithEmptyContent() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {}
+				}
+				""";
+
+		String contentJson = """
+				{}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+	}
+
+	@Test
+	void testValidateWithNestedObjectSchema() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"person": {
+							"type": "object",
+							"properties": {
+								"name": {"type": "string"},
+								"address": {
+									"type": "object",
+									"properties": {
+										"street": {"type": "string"},
+										"city": {"type": "string"}
+									},
+									"required": ["street", "city"]
+								}
+							},
+							"required": ["name", "address"]
+						}
+					},
+					"required": ["person"]
+				}
+				""";
+
+		String contentJson = """
+				{
+					"person": {
+						"name": "John Doe",
+						"address": {
+							"street": "123 Main St",
+							"city": "Anytown"
+						}
+					}
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+	}
+
+	@Test
+	void testValidateWithInvalidNestedObjectSchema() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"person": {
+							"type": "object",
+							"properties": {
+								"name": {"type": "string"},
+								"address": {
+									"type": "object",
+									"properties": {
+										"street": {"type": "string"},
+										"city": {"type": "string"}
+									},
+									"required": ["street", "city"]
+								}
+							},
+							"required": ["name", "address"]
+						}
+					},
+					"required": ["person"]
+				}
+				""";
+
+		String contentJson = """
+				{
+					"person": {
+						"name": "John Doe",
+						"address": {
+							"street": "123 Main St"
+						}
+					}
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertFalse(response.valid());
+		assertNotNull(response.errorMessage());
+		assertTrue(response.errorMessage().contains("Validation failed"));
+	}
+
+	@Test
+	void testValidateWithJsonProcessingException() throws Exception {
+		DefaultJsonSchemaValidator validatorWithMockMapper = new DefaultJsonSchemaValidator(mockObjectMapper);
+
+		Map<String, Object> schema = Map.of("type", "object");
+		Map<String, Object> structuredContent = Map.of("key", "value");
+
+		// This will trigger our null check and throw JsonProcessingException
+		when(mockObjectMapper.valueToTree(any())).thenReturn(null);
+
+		ValidationResponse response = validatorWithMockMapper.validate(schema, structuredContent);
+
+		assertFalse(response.valid());
+		assertNotNull(response.errorMessage());
+		assertTrue(response.errorMessage().contains("Error parsing tool JSON Schema"));
+		assertTrue(response.errorMessage().contains("Failed to convert schema to JsonNode"));
+	}
+
+	@ParameterizedTest
+	@MethodSource("provideValidSchemaAndContentPairs")
+	void testValidateWithVariousValidInputs(Map<String, Object> schema, Map<String, Object> content) {
+		ValidationResponse response = validator.validate(schema, content);
+
+		assertTrue(response.valid(), "Expected validation to pass for schema: " + schema + " and content: " + content);
+		assertNull(response.errorMessage());
+	}
+
+	@ParameterizedTest
+	@MethodSource("provideInvalidSchemaAndContentPairs")
+	void testValidateWithVariousInvalidInputs(Map<String, Object> schema, Map<String, Object> content) {
+		ValidationResponse response = validator.validate(schema, content);
+
+		assertFalse(response.valid(), "Expected validation to fail for schema: " + schema + " and content: " + content);
+		assertNotNull(response.errorMessage());
+		assertTrue(response.errorMessage().contains("Validation failed"));
+	}
+
+	private static Map<String, Object> staticToMap(String json) {
+		try {
+			ObjectMapper mapper = new ObjectMapper();
+			return mapper.readValue(json, new TypeReference<Map<String, Object>>() {
+			});
+		}
+		catch (Exception e) {
+			throw new RuntimeException("Failed to parse JSON: " + json, e);
+		}
+	}
+
+	private static Stream<Arguments> provideValidSchemaAndContentPairs() {
+		return Stream.of(
+				// Boolean schema
+				Arguments.of(staticToMap("""
+						{
+							"type": "object",
+							"properties": {
+								"flag": {"type": "boolean"}
+							}
+						}
+						"""), staticToMap("""
+						{
+							"flag": true
+						}
+						""")),
+				// String with additional properties allowed
+				Arguments.of(staticToMap("""
+						{
+							"type": "object",
+							"properties": {
+								"name": {"type": "string"}
+							},
+							"additionalProperties": true
+						}
+						"""), staticToMap("""
+						{
+							"name": "test",
+							"extra": "allowed"
+						}
+						""")),
+				// Array with specific items
+				Arguments.of(staticToMap("""
+						{
+							"type": "object",
+							"properties": {
+								"numbers": {
+									"type": "array",
+									"items": {"type": "number"}
+								}
+							}
+						}
+						"""), staticToMap("""
+						{
+							"numbers": [1.0, 2.5, 3.14]
+						}
+						""")),
+				// Enum validation
+				Arguments.of(staticToMap("""
+						{
+							"type": "object",
+							"properties": {
+								"status": {
+									"type": "string",
+									"enum": ["active", "inactive", "pending"]
+								}
+							}
+						}
+						"""), staticToMap("""
+						{
+							"status": "active"
+						}
+						""")));
+	}
+
+	private static Stream<Arguments> provideInvalidSchemaAndContentPairs() {
+		return Stream.of(
+				// Wrong boolean type
+				Arguments.of(staticToMap("""
+						{
+							"type": "object",
+							"properties": {
+								"flag": {"type": "boolean"}
+							}
+						}
+						"""), staticToMap("""
+						{
+							"flag": "true"
+						}
+						""")),
+				// Array with wrong item types
+				Arguments.of(staticToMap("""
+						{
+							"type": "object",
+							"properties": {
+								"numbers": {
+									"type": "array",
+									"items": {"type": "number"}
+								}
+							}
+						}
+						"""), staticToMap("""
+						{
+							"numbers": ["one", "two", "three"]
+						}
+						""")),
+				// Invalid enum value
+				Arguments.of(staticToMap("""
+						{
+							"type": "object",
+							"properties": {
+								"status": {
+									"type": "string",
+									"enum": ["active", "inactive", "pending"]
+								}
+							}
+						}
+						"""), staticToMap("""
+						{
+							"status": "unknown"
+						}
+						""")),
+				// Minimum constraint violation
+				Arguments.of(staticToMap("""
+						{
+							"type": "object",
+							"properties": {
+								"age": {"type": "integer", "minimum": 0}
+							}
+						}
+						"""), staticToMap("""
+						{
+							"age": -5
+						}
+						""")));
+	}
+
+	@Test
+	void testValidationResponseToValid() {
+		String jsonOutput = "{\"test\":\"value\"}";
+		ValidationResponse response = ValidationResponse.asValid(jsonOutput);
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+		assertEquals(jsonOutput, response.jsonStructuredOutput());
+	}
+
+	@Test
+	void testValidationResponseToInvalid() {
+		String errorMessage = "Test error message";
+		ValidationResponse response = ValidationResponse.asInvalid(errorMessage);
+		assertFalse(response.valid());
+		assertEquals(errorMessage, response.errorMessage());
+		assertNull(response.jsonStructuredOutput());
+	}
+
+	@Test
+	void testValidationResponseRecord() {
+		ValidationResponse response1 = new ValidationResponse(true, null, "{\"valid\":true}");
+		ValidationResponse response2 = new ValidationResponse(false, "Error", null);
+
+		assertTrue(response1.valid());
+		assertNull(response1.errorMessage());
+		assertEquals("{\"valid\":true}", response1.jsonStructuredOutput());
+
+		assertFalse(response2.valid());
+		assertEquals("Error", response2.errorMessage());
+		assertNull(response2.jsonStructuredOutput());
+
+		// Test equality
+		ValidationResponse response3 = new ValidationResponse(true, null, "{\"valid\":true}");
+		assertEquals(response1, response3);
+		assertNotEquals(response1, response2);
+	}
+
+}

mcp-json-jackson2/src/test/java/io/modelcontextprotocol/json/jackson2/DefaultJsonSchemaValidatorTests.java

@@ -0,0 +1,808 @@
+/*
+ * Copyright 2026-2026 the original author or authors.
+ */
+
+package io.modelcontextprotocol.json.jackson2;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.when;
+
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Stream;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+
+import com.fasterxml.jackson.core.type.TypeReference;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+import io.modelcontextprotocol.json.schema.JsonSchemaValidator.ValidationResponse;
+import io.modelcontextprotocol.json.schema.jackson2.DefaultJsonSchemaValidator;
+
+/**
+ * Tests for {@link DefaultJsonSchemaValidator}.
+ *
+ * @author Christian Tzolov
+ */
+class DefaultJsonSchemaValidatorTests {
+
+	private DefaultJsonSchemaValidator validator;
+
+	private ObjectMapper objectMapper;
+
+	@Mock
+	private ObjectMapper mockObjectMapper;
+
+	@BeforeEach
+	void setUp() {
+		MockitoAnnotations.openMocks(this);
+		validator = new DefaultJsonSchemaValidator();
+		objectMapper = new ObjectMapper();
+	}
+
+	/**
+	 * Utility method to convert JSON string to Map<String, Object>
+	 */
+	private Map<String, Object> toMap(String json) {
+		try {
+			return objectMapper.readValue(json, new TypeReference<Map<String, Object>>() {
+			});
+		}
+		catch (Exception e) {
+			throw new RuntimeException("Failed to parse JSON: " + json, e);
+		}
+	}
+
+	private List<Map<String, Object>> toListMap(String json) {
+		try {
+			return objectMapper.readValue(json, new TypeReference<List<Map<String, Object>>>() {
+			});
+		}
+		catch (Exception e) {
+			throw new RuntimeException("Failed to parse JSON: " + json, e);
+		}
+	}
+
+	@Test
+	void testDefaultConstructor() {
+		DefaultJsonSchemaValidator defaultValidator = new DefaultJsonSchemaValidator();
+
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"test": {"type": "string"}
+					}
+				}
+				""";
+		String contentJson = """
+				{
+					"test": "value"
+				}
+				""";
+
+		ValidationResponse response = defaultValidator.validate(toMap(schemaJson), toMap(contentJson));
+		assertTrue(response.valid());
+	}
+
+	@Test
+	void testConstructorWithObjectMapper() {
+		ObjectMapper customMapper = new ObjectMapper();
+		DefaultJsonSchemaValidator customValidator = new DefaultJsonSchemaValidator(customMapper);
+
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"test": {"type": "string"}
+					}
+				}
+				""";
+		String contentJson = """
+				{
+					"test": "value"
+				}
+				""";
+
+		ValidationResponse response = customValidator.validate(toMap(schemaJson), toMap(contentJson));
+		assertTrue(response.valid());
+	}
+
+	@Test
+	void testValidateWithValidStringSchema() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"name": {"type": "string"},
+						"age": {"type": "integer"}
+					},
+					"required": ["name", "age"]
+				}
+				""";
+
+		String contentJson = """
+				{
+					"name": "John Doe",
+					"age": 30
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+		assertNotNull(response.jsonStructuredOutput());
+	}
+
+	@Test
+	void testValidateWithValidNumberSchema() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"price": {"type": "number", "minimum": 0},
+						"quantity": {"type": "integer", "minimum": 1}
+					},
+					"required": ["price", "quantity"]
+				}
+				""";
+
+		String contentJson = """
+				{
+					"price": 19.99,
+					"quantity": 5
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+	}
+
+	@Test
+	void testValidateWithValidArraySchema() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"items": {
+							"type": "array",
+							"items": {"type": "string"}
+						}
+					},
+					"required": ["items"]
+				}
+				""";
+
+		String contentJson = """
+				{
+					"items": ["apple", "banana", "cherry"]
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+	}
+
+	@Test
+	void testValidateWithValidArraySchemaTopLevelArray() {
+		String schemaJson = """
+				{
+					"$schema" : "https://json-schema.org/draft/2020-12/schema",
+					"type" : "array",
+					"items" : {
+						"type" : "object",
+						"properties" : {
+						"city" : {
+							"type" : "string"
+						},
+						"summary" : {
+							"type" : "string"
+						},
+						"temperatureC" : {
+							"type" : "number",
+							"format" : "float"
+						}
+						},
+						"required" : [ "city", "summary", "temperatureC" ]
+					},
+					"additionalProperties" : false
+				}
+					""";
+
+		String contentJson = """
+				[
+					{
+						"city": "London",
+						"summary": "Generally mild with frequent rainfall. Winters are cool and damp, summers are warm but rarely hot. Cloudy conditions are common throughout the year.",
+						"temperatureC": 11.3
+					},
+					{
+						"city": "New York",
+						"summary": "Four distinct seasons with hot and humid summers, cold winters with snow, and mild springs and autumns. Precipitation is fairly evenly distributed throughout the year.",
+						"temperatureC": 12.8
+					},
+					{
+						"city": "San Francisco",
+						"summary": "Mild year-round with a distinctive Mediterranean climate. Famous for summer fog, mild winters, and little temperature variation throughout the year. Very little rainfall in summer months.",
+						"temperatureC": 14.6
+					},
+					{
+						"city": "Tokyo",
+						"summary": "Humid subtropical climate with hot, wet summers and mild winters. Experiences a rainy season in early summer and occasional typhoons in late summer to early autumn.",
+						"temperatureC": 15.4
+					}
+				]
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+
+		// Validate as JSON string
+		ValidationResponse response = validator.validate(schema, contentJson);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+
+		List<Map<String, Object>> structuredContent = toListMap(contentJson);
+
+		// Validate as List<Map<String, Object>>
+		response = validator.validate(schema, structuredContent);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+	}
+
+	@Test
+	void testValidateWithInvalidTypeSchema() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"name": {"type": "string"},
+						"age": {"type": "integer"}
+					},
+					"required": ["name", "age"]
+				}
+				""";
+
+		String contentJson = """
+				{
+					"name": "John Doe",
+					"age": "thirty"
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertFalse(response.valid());
+		assertNotNull(response.errorMessage());
+		assertTrue(response.errorMessage().contains("Validation failed"));
+		assertTrue(response.errorMessage().contains("structuredContent does not match tool outputSchema"));
+	}
+
+	@Test
+	void testValidateWithMissingRequiredField() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"name": {"type": "string"},
+						"age": {"type": "integer"}
+					},
+					"required": ["name", "age"]
+				}
+				""";
+
+		String contentJson = """
+				{
+					"name": "John Doe"
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertFalse(response.valid());
+		assertNotNull(response.errorMessage());
+		assertTrue(response.errorMessage().contains("Validation failed"));
+	}
+
+	@Test
+	void testValidateWithAdditionalPropertiesNotAllowed() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"name": {"type": "string"}
+					},
+					"required": ["name"],
+					"additionalProperties": false
+				}
+				""";
+
+		String contentJson = """
+				{
+					"name": "John Doe",
+					"extraField": "should not be allowed"
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertFalse(response.valid());
+		assertNotNull(response.errorMessage());
+		assertTrue(response.errorMessage().contains("Validation failed"));
+	}
+
+	@Test
+	void testValidateWithAdditionalPropertiesExplicitlyAllowed() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"name": {"type": "string"}
+					},
+					"required": ["name"],
+					"additionalProperties": true
+				}
+				""";
+
+		String contentJson = """
+				{
+					"name": "John Doe",
+					"extraField": "should be allowed"
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+	}
+
+	@Test
+	void testValidateWithDefaultAdditionalProperties() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"name": {"type": "string"}
+					},
+					"required": ["name"],
+					"additionalProperties": true
+				}
+				""";
+
+		String contentJson = """
+				{
+					"name": "John Doe",
+					"extraField": "should be allowed"
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+	}
+
+	@Test
+	void testValidateWithAdditionalPropertiesExplicitlyDisallowed() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"name": {"type": "string"}
+					},
+					"required": ["name"],
+					"additionalProperties": false
+				}
+				""";
+
+		String contentJson = """
+				{
+					"name": "John Doe",
+					"extraField": "should not be allowed"
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertFalse(response.valid());
+		assertNotNull(response.errorMessage());
+		assertTrue(response.errorMessage().contains("Validation failed"));
+	}
+
+	@Test
+	void testValidateWithEmptySchema() {
+		String schemaJson = """
+				{
+					"additionalProperties": true
+				}
+				""";
+
+		String contentJson = """
+				{
+					"anything": "goes"
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+	}
+
+	@Test
+	void testValidateWithEmptyContent() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {}
+				}
+				""";
+
+		String contentJson = """
+				{}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+	}
+
+	@Test
+	void testValidateWithNestedObjectSchema() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"person": {
+							"type": "object",
+							"properties": {
+								"name": {"type": "string"},
+								"address": {
+									"type": "object",
+									"properties": {
+										"street": {"type": "string"},
+										"city": {"type": "string"}
+									},
+									"required": ["street", "city"]
+								}
+							},
+							"required": ["name", "address"]
+						}
+					},
+					"required": ["person"]
+				}
+				""";
+
+		String contentJson = """
+				{
+					"person": {
+						"name": "John Doe",
+						"address": {
+							"street": "123 Main St",
+							"city": "Anytown"
+						}
+					}
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+	}
+
+	@Test
+	void testValidateWithInvalidNestedObjectSchema() {
+		String schemaJson = """
+				{
+					"type": "object",
+					"properties": {
+						"person": {
+							"type": "object",
+							"properties": {
+								"name": {"type": "string"},
+								"address": {
+									"type": "object",
+									"properties": {
+										"street": {"type": "string"},
+										"city": {"type": "string"}
+									},
+									"required": ["street", "city"]
+								}
+							},
+							"required": ["name", "address"]
+						}
+					},
+					"required": ["person"]
+				}
+				""";
+
+		String contentJson = """
+				{
+					"person": {
+						"name": "John Doe",
+						"address": {
+							"street": "123 Main St"
+						}
+					}
+				}
+				""";
+
+		Map<String, Object> schema = toMap(schemaJson);
+		Map<String, Object> structuredContent = toMap(contentJson);
+
+		ValidationResponse response = validator.validate(schema, structuredContent);
+
+		assertFalse(response.valid());
+		assertNotNull(response.errorMessage());
+		assertTrue(response.errorMessage().contains("Validation failed"));
+	}
+
+	@Test
+	void testValidateWithJsonProcessingException() throws Exception {
+		DefaultJsonSchemaValidator validatorWithMockMapper = new DefaultJsonSchemaValidator(mockObjectMapper);
+
+		Map<String, Object> schema = Map.of("type", "object");
+		Map<String, Object> structuredContent = Map.of("key", "value");
+
+		// This will trigger our null check and throw JsonProcessingException
+		when(mockObjectMapper.valueToTree(any())).thenReturn(null);
+
+		ValidationResponse response = validatorWithMockMapper.validate(schema, structuredContent);
+
+		assertFalse(response.valid());
+		assertNotNull(response.errorMessage());
+		assertTrue(response.errorMessage().contains("Error parsing tool JSON Schema"));
+		assertTrue(response.errorMessage().contains("Failed to convert schema to JsonNode"));
+	}
+
+	@ParameterizedTest
+	@MethodSource("provideValidSchemaAndContentPairs")
+	void testValidateWithVariousValidInputs(Map<String, Object> schema, Map<String, Object> content) {
+		ValidationResponse response = validator.validate(schema, content);
+
+		assertTrue(response.valid(), "Expected validation to pass for schema: " + schema + " and content: " + content);
+		assertNull(response.errorMessage());
+	}
+
+	@ParameterizedTest
+	@MethodSource("provideInvalidSchemaAndContentPairs")
+	void testValidateWithVariousInvalidInputs(Map<String, Object> schema, Map<String, Object> content) {
+		ValidationResponse response = validator.validate(schema, content);
+
+		assertFalse(response.valid(), "Expected validation to fail for schema: " + schema + " and content: " + content);
+		assertNotNull(response.errorMessage());
+		assertTrue(response.errorMessage().contains("Validation failed"));
+	}
+
+	private static Map<String, Object> staticToMap(String json) {
+		try {
+			ObjectMapper mapper = new ObjectMapper();
+			return mapper.readValue(json, new TypeReference<Map<String, Object>>() {
+			});
+		}
+		catch (Exception e) {
+			throw new RuntimeException("Failed to parse JSON: " + json, e);
+		}
+	}
+
+	private static Stream<Arguments> provideValidSchemaAndContentPairs() {
+		return Stream.of(
+				// Boolean schema
+				Arguments.of(staticToMap("""
+						{
+							"type": "object",
+							"properties": {
+								"flag": {"type": "boolean"}
+							}
+						}
+						"""), staticToMap("""
+						{
+							"flag": true
+						}
+						""")),
+				// String with additional properties allowed
+				Arguments.of(staticToMap("""
+						{
+							"type": "object",
+							"properties": {
+								"name": {"type": "string"}
+							},
+							"additionalProperties": true
+						}
+						"""), staticToMap("""
+						{
+							"name": "test",
+							"extra": "allowed"
+						}
+						""")),
+				// Array with specific items
+				Arguments.of(staticToMap("""
+						{
+							"type": "object",
+							"properties": {
+								"numbers": {
+									"type": "array",
+									"items": {"type": "number"}
+								}
+							}
+						}
+						"""), staticToMap("""
+						{
+							"numbers": [1.0, 2.5, 3.14]
+						}
+						""")),
+				// Enum validation
+				Arguments.of(staticToMap("""
+						{
+							"type": "object",
+							"properties": {
+								"status": {
+									"type": "string",
+									"enum": ["active", "inactive", "pending"]
+								}
+							}
+						}
+						"""), staticToMap("""
+						{
+							"status": "active"
+						}
+						""")));
+	}
+
+	private static Stream<Arguments> provideInvalidSchemaAndContentPairs() {
+		return Stream.of(
+				// Wrong boolean type
+				Arguments.of(staticToMap("""
+						{
+							"type": "object",
+							"properties": {
+								"flag": {"type": "boolean"}
+							}
+						}
+						"""), staticToMap("""
+						{
+							"flag": "true"
+						}
+						""")),
+				// Array with wrong item types
+				Arguments.of(staticToMap("""
+						{
+							"type": "object",
+							"properties": {
+								"numbers": {
+									"type": "array",
+									"items": {"type": "number"}
+								}
+							}
+						}
+						"""), staticToMap("""
+						{
+							"numbers": ["one", "two", "three"]
+						}
+						""")),
+				// Invalid enum value
+				Arguments.of(staticToMap("""
+						{
+							"type": "object",
+							"properties": {
+								"status": {
+									"type": "string",
+									"enum": ["active", "inactive", "pending"]
+								}
+							}
+						}
+						"""), staticToMap("""
+						{
+							"status": "unknown"
+						}
+						""")),
+				// Minimum constraint violation
+				Arguments.of(staticToMap("""
+						{
+							"type": "object",
+							"properties": {
+								"age": {"type": "integer", "minimum": 0}
+							}
+						}
+						"""), staticToMap("""
+						{
+							"age": -5
+						}
+						""")));
+	}
+
+	@Test
+	void testValidationResponseToValid() {
+		String jsonOutput = "{\"test\":\"value\"}";
+		ValidationResponse response = ValidationResponse.asValid(jsonOutput);
+		assertTrue(response.valid());
+		assertNull(response.errorMessage());
+		assertEquals(jsonOutput, response.jsonStructuredOutput());
+	}
+
+	@Test
+	void testValidationResponseToInvalid() {
+		String errorMessage = "Test error message";
+		ValidationResponse response = ValidationResponse.asInvalid(errorMessage);
+		assertFalse(response.valid());
+		assertEquals(errorMessage, response.errorMessage());
+		assertNull(response.jsonStructuredOutput());
+	}
+
+	@Test
+	void testValidationResponseRecord() {
+		ValidationResponse response1 = new ValidationResponse(true, null, "{\"valid\":true}");
+		ValidationResponse response2 = new ValidationResponse(false, "Error", null);
+
+		assertTrue(response1.valid());
+		assertNull(response1.errorMessage());
+		assertEquals("{\"valid\":true}", response1.jsonStructuredOutput());
+
+		assertFalse(response2.valid());
+		assertEquals("Error", response2.errorMessage());
+		assertNull(response2.jsonStructuredOutput());
+
+		// Test equality
+		ValidationResponse response3 = new ValidationResponse(true, null, "{\"valid\":true}");
+		assertEquals(response1, response3);
+		assertNotEquals(response1, response2);
+	}
+
+}

mcp-json-jackson2/src/test/java/io/modelcontextprotocol/json/schema/JsonSchemaValidatorTest.java

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2026-2026 the original author or authors.
+ */
+
+package io.modelcontextprotocol.json.schema;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+import io.modelcontextprotocol.json.schema.jackson2.DefaultJsonSchemaValidator;
+
+class JsonSchemaValidatorTest {
+
+	@Test
+	void shouldUseJackson2Mapper() {
+		assertThat(JsonSchemaValidator.getDefault()).isInstanceOf(DefaultJsonSchemaValidator.class);
+	}
+
+}

mcp-json-jackson3/pom.xml

@@ -0,0 +1,79 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	<parent>
+		<groupId>io.modelcontextprotocol.sdk</groupId>
+		<artifactId>mcp-parent</artifactId>
+		<version>0.18.0-SNAPSHOT</version>
+	</parent>
+	<artifactId>mcp-json-jackson3</artifactId>
+	<packaging>jar</packaging>
+	<name>Java MCP SDK JSON Jackson</name>
+	<description>Java MCP SDK JSON implementation based on Jackson 3</description>
+	<url>https://github.com/modelcontextprotocol/java-sdk</url>
+	<scm>
+		<url>https://github.com/modelcontextprotocol/java-sdk</url>
+		<connection>git://github.com/modelcontextprotocol/java-sdk.git</connection>
+		<developerConnection>git@github.com/modelcontextprotocol/java-sdk.git</developerConnection>
+	</scm>
+	<build>
+		<plugins>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-jar-plugin</artifactId>
+				<configuration>
+					<archive>
+                        <manifest>
+                            <addDefaultImplementationEntries>true</addDefaultImplementationEntries>
+                        </manifest>
+					</archive>
+				</configuration>
+			</plugin>
+		</plugins>
+	</build>
+	<dependencies>
+        <dependency>
+            <groupId>io.modelcontextprotocol.sdk</groupId>
+            <artifactId>mcp-json</artifactId>
+            <version>0.18.0-SNAPSHOT</version>
+        </dependency>
+        <dependency>
+            <groupId>tools.jackson.core</groupId>
+            <artifactId>jackson-databind</artifactId>
+            <version>${jackson3.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.networknt</groupId>
+            <artifactId>json-schema-validator</artifactId>
+            <version>${json-schema-validator-jackson3.version}</version>
+        </dependency>
+
+		<dependency>
+			<groupId>org.assertj</groupId>
+			<artifactId>assertj-core</artifactId>
+			<version>${assert4j.version}</version>
+			<scope>test</scope>
+		</dependency>
+		<dependency>
+			<groupId>org.junit.jupiter</groupId>
+			<artifactId>junit-jupiter-api</artifactId>
+			<version>${junit.version}</version>
+			<scope>test</scope>
+		</dependency>
+		<dependency>
+			<groupId>org.junit.jupiter</groupId>
+			<artifactId>junit-jupiter-params</artifactId>
+			<version>${junit.version}</version>
+			<scope>test</scope>
+		</dependency>
+		<dependency>
+			<groupId>org.mockito</groupId>
+			<artifactId>mockito-core</artifactId>
+			<version>${mockito.version}</version>
+			<scope>test</scope>
+		</dependency>
+
+	</dependencies>
+</project>

mcp-json-jackson3/src/main/java/io/modelcontextprotocol/json/jackson3/JacksonMcpJsonMapper.java

@@ -0,0 +1,119 @@
+/*
+ * Copyright 2026 - 2026 the original author or authors.
+ */
+
+package io.modelcontextprotocol.json.jackson3;
+
+import java.io.IOException;
+
+import io.modelcontextprotocol.json.McpJsonMapper;
+import io.modelcontextprotocol.json.TypeRef;
+
+import tools.jackson.core.JacksonException;
+import tools.jackson.databind.JavaType;
+import tools.jackson.databind.json.JsonMapper;
+
+/**
+ * Jackson-based implementation of JsonMapper. Wraps a Jackson JsonMapper but keeps the
+ * SDK decoupled from Jackson at the API level.
+ */
+public final class JacksonMcpJsonMapper implements McpJsonMapper {
+
+	private final JsonMapper jsonMapper;
+
+	/**
+	 * Constructs a new JacksonMcpJsonMapper instance with the given JsonMapper.
+	 * @param jsonMapper the JsonMapper to be used for JSON serialization and
+	 * deserialization. Must not be null.
+	 * @throws IllegalArgumentException if the provided JsonMapper is null.
+	 */
+	public JacksonMcpJsonMapper(JsonMapper jsonMapper) {
+		if (jsonMapper == null) {
+			throw new IllegalArgumentException("JsonMapper must not be null");
+		}
+		this.jsonMapper = jsonMapper;
+	}
+
+	/**
+	 * Returns the underlying Jackson {@link JsonMapper} used for JSON serialization and
+	 * deserialization.
+	 * @return the JsonMapper instance
+	 */
+	public JsonMapper getJsonMapper() {
+		return jsonMapper;
+	}
+
+	@Override
+	public <T> T readValue(String content, Class<T> type) throws IOException {
+		try {
+			return jsonMapper.readValue(content, type);
+		}
+		catch (JacksonException ex) {
+			throw new IOException("Failed to read value", ex);
+		}
+	}
+
+	@Override
+	public <T> T readValue(byte[] content, Class<T> type) throws IOException {
+		try {
+			return jsonMapper.readValue(content, type);
+		}
+		catch (JacksonException ex) {
+			throw new IOException("Failed to read value", ex);
+		}
+	}
+
+	@Override
+	public <T> T readValue(String content, TypeRef<T> type) throws IOException {
+		JavaType javaType = jsonMapper.getTypeFactory().constructType(type.getType());
+		try {
+			return jsonMapper.readValue(content, javaType);
+		}
+		catch (JacksonException ex) {
+			throw new IOException("Failed to read value", ex);
+		}
+	}
+
+	@Override
+	public <T> T readValue(byte[] content, TypeRef<T> type) throws IOException {
+		JavaType javaType = jsonMapper.getTypeFactory().constructType(type.getType());
+		try {
+			return jsonMapper.readValue(content, javaType);
+		}
+		catch (JacksonException ex) {
+			throw new IOException("Failed to read value", ex);
+		}
+	}
+
+	@Override
+	public <T> T convertValue(Object fromValue, Class<T> type) {
+		return jsonMapper.convertValue(fromValue, type);
+	}
+
+	@Override
+	public <T> T convertValue(Object fromValue, TypeRef<T> type) {
+		JavaType javaType = jsonMapper.getTypeFactory().constructType(type.getType());
+		return jsonMapper.convertValue(fromValue, javaType);
+	}
+
+	@Override
+	public String writeValueAsString(Object value) throws IOException {
+		try {
+			return jsonMapper.writeValueAsString(value);
+		}
+		catch (JacksonException ex) {
+			throw new IOException("Failed to write value as string", ex);
+		}
+	}
+
+	@Override
+	public byte[] writeValueAsBytes(Object value) throws IOException {
+		try {
+			return jsonMapper.writeValueAsBytes(value);
+		}
+		catch (JacksonException ex) {
+			throw new IOException("Failed to write value as bytes", ex);
+		}
+	}
+
+}

mcp-json-jackson3/src/main/java/io/modelcontextprotocol/json/jackson3/JacksonMcpJsonMapperSupplier.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2026 - 2026 the original author or authors.
+ */
+
+package io.modelcontextprotocol.json.jackson3;
+
+import tools.jackson.databind.json.JsonMapper;
+
+import io.modelcontextprotocol.json.McpJsonMapper;
+import io.modelcontextprotocol.json.McpJsonMapperSupplier;
+
+/**
+ * A supplier of {@link McpJsonMapper} instances that uses the Jackson library for JSON
+ * serialization and deserialization.
+ * <p>
+ * This implementation provides a {@link McpJsonMapper} backed by
+ * {@link JsonMapper#shared() JsonMapper shared instance}.
+ */
+public class JacksonMcpJsonMapperSupplier implements McpJsonMapperSupplier {
+
+	/**
+	 * Returns a new instance of {@link McpJsonMapper} that uses the Jackson library for
+	 * JSON serialization and deserialization.
+	 * <p>
+	 * The returned {@link McpJsonMapper} is backed by {@link JsonMapper#shared()
+	 * JsonMapper shared instance}.
+	 * @return a new {@link McpJsonMapper} instance
+	 */
+	@Override
+	public McpJsonMapper get() {
+		return new JacksonMcpJsonMapper(JsonMapper.shared());
+	}
+
+}