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feat!: add tool input arguments validation (#873)

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added tool input arguments validation causes tool execution error. Breaking change, because validation is activated by default

closes #697

Signed-off-by: Daniel Garnier-Moiroux <git@garnier.wf>
This commit is contained in:
ashakirin 2026-04-13 16:58:04 +02:00 • committed by GitHub
commit d1823389a9
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GPG key ID: B5690EEEBB952194
4 changed files with 496 additions and 9 deletions
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18
mcp-core/src/main/java/io/modelcontextprotocol/server/McpAsyncServer.java
View file

@ -38,6 +38,7 @@ import io.modelcontextprotocol.spec.McpStreamableServerTransportProvider;
import io.modelcontextprotocol.util.Assert;
import io.modelcontextprotocol.util.DefaultMcpUriTemplateManagerFactory;
import io.modelcontextprotocol.util.McpUriTemplateManagerFactory;
import io.modelcontextprotocol.util.ToolInputValidator;
import io.modelcontextprotocol.util.Utils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
@ -98,6 +99,8 @@ public class McpAsyncServer {
private final JsonSchemaValidator jsonSchemaValidator;
private final boolean validateToolInputs;
private final McpSchema.ServerCapabilities serverCapabilities;
private final McpSchema.Implementation serverInfo;
@ -129,7 +132,8 @@ public class McpAsyncServer {
*/
McpAsyncServer(McpServerTransportProvider mcpTransportProvider, McpJsonMapper jsonMapper,
McpServerFeatures.Async features, Duration requestTimeout,
McpUriTemplateManagerFactory uriTemplateManagerFactory, JsonSchemaValidator jsonSchemaValidator) {
McpUriTemplateManagerFactory uriTemplateManagerFactory, JsonSchemaValidator jsonSchemaValidator,
boolean validateToolInputs) {
this.mcpTransportProvider = mcpTransportProvider;
this.jsonMapper = jsonMapper;
this.serverInfo = features.serverInfo();
@ -142,6 +146,7 @@ public class McpAsyncServer {
this.completions.putAll(features.completions());
this.uriTemplateManagerFactory = uriTemplateManagerFactory;
this.jsonSchemaValidator = jsonSchemaValidator;
this.validateToolInputs = validateToolInputs;
Map<String, McpRequestHandler<?>> requestHandlers = prepareRequestHandlers();
Map<String, McpNotificationHandler> notificationHandlers = prepareNotificationHandlers(features);
@ -157,7 +162,8 @@ public class McpAsyncServer {
McpAsyncServer(McpStreamableServerTransportProvider mcpTransportProvider, McpJsonMapper jsonMapper,
McpServerFeatures.Async features, Duration requestTimeout,
McpUriTemplateManagerFactory uriTemplateManagerFactory, JsonSchemaValidator jsonSchemaValidator) {
McpUriTemplateManagerFactory uriTemplateManagerFactory, JsonSchemaValidator jsonSchemaValidator,
boolean validateToolInputs) {
this.mcpTransportProvider = mcpTransportProvider;
this.jsonMapper = jsonMapper;
this.serverInfo = features.serverInfo();
@ -170,6 +176,7 @@ public class McpAsyncServer {
this.completions.putAll(features.completions());
this.uriTemplateManagerFactory = uriTemplateManagerFactory;
this.jsonSchemaValidator = jsonSchemaValidator;
this.validateToolInputs = validateToolInputs;
Map<String, McpRequestHandler<?>> requestHandlers = prepareRequestHandlers();
Map<String, McpNotificationHandler> notificationHandlers = prepareNotificationHandlers(features);
@ -543,6 +550,13 @@ public class McpAsyncServer {
.build());
}
McpSchema.Tool tool = toolSpecification.get().tool();
CallToolResult validationError = ToolInputValidator.validate(tool, callToolRequest.arguments(),
this.validateToolInputs, this.jsonSchemaValidator);
if (validationError != null) {
return Mono.just(validationError);
}
return toolSpecification.get().callHandler().apply(exchange, callToolRequest);
};
}

67
mcp-core/src/main/java/io/modelcontextprotocol/server/McpServer.java
View file

@ -243,7 +243,7 @@ public interface McpServer {
: McpJsonDefaults.getSchemaValidator();
return new McpAsyncServer(transportProvider, jsonMapper == null ? McpJsonDefaults.getMapper() : jsonMapper,
features, requestTimeout, uriTemplateManagerFactory, jsonSchemaValidator);
features, requestTimeout, uriTemplateManagerFactory, jsonSchemaValidator, validateToolInputs);
}
}
@ -269,7 +269,7 @@ public interface McpServer {
var jsonSchemaValidator = this.jsonSchemaValidator != null ? this.jsonSchemaValidator
: McpJsonDefaults.getSchemaValidator();
return new McpAsyncServer(transportProvider, jsonMapper == null ? McpJsonDefaults.getMapper() : jsonMapper,
features, requestTimeout, uriTemplateManagerFactory, jsonSchemaValidator);
features, requestTimeout, uriTemplateManagerFactory, jsonSchemaValidator, validateToolInputs);
}
}
@ -293,6 +293,8 @@ public interface McpServer {
boolean strictToolNameValidation = ToolNameValidator.isStrictByDefault();
boolean validateToolInputs = true;
/**
* The Model Context Protocol (MCP) allows servers to expose tools that can be
* invoked by language models. Tools enable models to interact with external
@ -421,6 +423,17 @@ public interface McpServer {
return this;
}
/**
* Sets whether to validate tool inputs against the tool's input schema.
* @param validate true to validate inputs and return error on validation failure,
* false to skip validation. Defaults to true.
* @return This builder instance for method chaining
*/
public AsyncSpecification<S> validateToolInputs(boolean validate) {
this.validateToolInputs = validate;
return this;
}
/**
* Sets the server capabilities that will be advertised to clients during
* connection initialization. Capabilities define what features the server
@ -818,7 +831,8 @@ public interface McpServer {
var asyncServer = new McpAsyncServer(transportProvider,
jsonMapper == null ? McpJsonDefaults.getMapper() : jsonMapper, asyncFeatures, requestTimeout,
uriTemplateManagerFactory,
jsonSchemaValidator != null ? jsonSchemaValidator : McpJsonDefaults.getSchemaValidator());
jsonSchemaValidator != null ? jsonSchemaValidator : McpJsonDefaults.getSchemaValidator(),
validateToolInputs);
return new McpSyncServer(asyncServer, this.immediateExecution);
}
@ -849,7 +863,7 @@ public interface McpServer {
: McpJsonDefaults.getSchemaValidator();
var asyncServer = new McpAsyncServer(transportProvider,
jsonMapper == null ? McpJsonDefaults.getMapper() : jsonMapper, asyncFeatures, this.requestTimeout,
this.uriTemplateManagerFactory, jsonSchemaValidator);
this.uriTemplateManagerFactory, jsonSchemaValidator, validateToolInputs);
return new McpSyncServer(asyncServer, this.immediateExecution);
}
@ -872,6 +886,8 @@ public interface McpServer {
boolean strictToolNameValidation = ToolNameValidator.isStrictByDefault();
boolean validateToolInputs = true;
/**
* The Model Context Protocol (MCP) allows servers to expose tools that can be
* invoked by language models. Tools enable models to interact with external
@ -1004,6 +1020,17 @@ public interface McpServer {
return this;
}
/**
* Sets whether to validate tool inputs against the tool's input schema.
* @param validate true to validate inputs and return error on validation failure,
* false to skip validation. Defaults to true.
* @return This builder instance for method chaining
*/
public SyncSpecification<S> validateToolInputs(boolean validate) {
this.validateToolInputs = validate;
return this;
}
/**
* Sets the server capabilities that will be advertised to clients during
* connection initialization. Capabilities define what features the server
@ -1401,6 +1428,8 @@ public interface McpServer {
boolean strictToolNameValidation = ToolNameValidator.isStrictByDefault();
boolean validateToolInputs = true;
/**
* The Model Context Protocol (MCP) allows servers to expose tools that can be
* invoked by language models. Tools enable models to interact with external
@ -1530,6 +1559,17 @@ public interface McpServer {
return this;
}
/**
* Sets whether to validate tool inputs against the tool's input schema.
* @param validate true to validate inputs and return error on validation failure,
* false to skip validation. Defaults to true.
* @return This builder instance for method chaining
*/
public StatelessAsyncSpecification validateToolInputs(boolean validate) {
this.validateToolInputs = validate;
return this;
}
/**
* Sets the server capabilities that will be advertised to clients during
* connection initialization. Capabilities define what features the server
@ -1859,7 +1899,8 @@ public interface McpServer {
this.resources, this.resourceTemplates, this.prompts, this.completions, this.instructions);
return new McpStatelessAsyncServer(transport, jsonMapper == null ? McpJsonDefaults.getMapper() : jsonMapper,
features, requestTimeout, uriTemplateManagerFactory,
jsonSchemaValidator != null ? jsonSchemaValidator : McpJsonDefaults.getSchemaValidator());
jsonSchemaValidator != null ? jsonSchemaValidator : McpJsonDefaults.getSchemaValidator(),
validateToolInputs);
}
}
@ -1884,6 +1925,8 @@ public interface McpServer {
boolean strictToolNameValidation = ToolNameValidator.isStrictByDefault();
boolean validateToolInputs = true;
/**
* The Model Context Protocol (MCP) allows servers to expose tools that can be
* invoked by language models. Tools enable models to interact with external
@ -2013,6 +2056,17 @@ public interface McpServer {
return this;
}
/**
* Sets whether to validate tool inputs against the tool's input schema.
* @param validate true to validate inputs and return error on validation failure,
* false to skip validation. Defaults to true.
* @return This builder instance for method chaining
*/
public StatelessSyncSpecification validateToolInputs(boolean validate) {
this.validateToolInputs = validate;
return this;
}
/**
* Sets the server capabilities that will be advertised to clients during
* connection initialization. Capabilities define what features the server
@ -2360,7 +2414,8 @@ public interface McpServer {
var asyncServer = new McpStatelessAsyncServer(transport,
jsonMapper == null ? McpJsonDefaults.getMapper() : jsonMapper, asyncFeatures, requestTimeout,
uriTemplateManagerFactory,
this.jsonSchemaValidator != null ? this.jsonSchemaValidator : McpJsonDefaults.getSchemaValidator());
this.jsonSchemaValidator != null ? this.jsonSchemaValidator : McpJsonDefaults.getSchemaValidator(),
validateToolInputs);
return new McpStatelessSyncServer(asyncServer, this.immediateExecution);
}

14
mcp-core/src/main/java/io/modelcontextprotocol/server/McpStatelessAsyncServer.java
View file

@ -21,6 +21,7 @@ import io.modelcontextprotocol.spec.McpStatelessServerTransport;
import io.modelcontextprotocol.util.Assert;
import io.modelcontextprotocol.util.DefaultMcpUriTemplateManagerFactory;
import io.modelcontextprotocol.util.McpUriTemplateManagerFactory;
import io.modelcontextprotocol.util.ToolInputValidator;
import io.modelcontextprotocol.util.Utils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
@ -77,9 +78,12 @@ public class McpStatelessAsyncServer {
private final JsonSchemaValidator jsonSchemaValidator;
private final boolean validateToolInputs;
McpStatelessAsyncServer(McpStatelessServerTransport mcpTransport, McpJsonMapper jsonMapper,
McpStatelessServerFeatures.Async features, Duration requestTimeout,
McpUriTemplateManagerFactory uriTemplateManagerFactory, JsonSchemaValidator jsonSchemaValidator) {
McpUriTemplateManagerFactory uriTemplateManagerFactory, JsonSchemaValidator jsonSchemaValidator,
boolean validateToolInputs) {
this.mcpTransportProvider = mcpTransport;
this.jsonMapper = jsonMapper;
this.serverInfo = features.serverInfo();
@ -92,6 +96,7 @@ public class McpStatelessAsyncServer {
this.completions.putAll(features.completions());
this.uriTemplateManagerFactory = uriTemplateManagerFactory;
this.jsonSchemaValidator = jsonSchemaValidator;
this.validateToolInputs = validateToolInputs;
Map<String, McpStatelessRequestHandler<?>> requestHandlers = new HashMap<>();
@ -409,6 +414,13 @@ public class McpStatelessAsyncServer {
.build());
}
McpSchema.Tool tool = toolSpecification.get().tool();
CallToolResult validationError = ToolInputValidator.validate(tool, callToolRequest.arguments(),
this.validateToolInputs, this.jsonSchemaValidator);
if (validationError != null) {
return Mono.just(validationError);
}
return toolSpecification.get().callHandler().apply(ctx, callToolRequest);
};
}

54
mcp-core/src/main/java/io/modelcontextprotocol/util/ToolInputValidator.java Normal file
View file

@ -0,0 +1,54 @@
/*
* Copyright 2026-2026 the original author or authors.
*/
package io.modelcontextprotocol.util;
import java.util.List;
import java.util.Map;
import io.modelcontextprotocol.json.schema.JsonSchemaValidator;
import io.modelcontextprotocol.spec.McpSchema;
import io.modelcontextprotocol.spec.McpSchema.CallToolResult;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Validates tool input arguments against JSON schema.
*
* @author Andrei Shakirin
*/
public final class ToolInputValidator {
private static final Logger logger = LoggerFactory.getLogger(ToolInputValidator.class);
private ToolInputValidator() {
}
/**
* Validates tool arguments against the tool's input schema.
* @param tool the tool definition containing the input schema
* @param arguments the arguments to validate
* @param validateToolInputs whether validation is enabled
* @param validator the JSON schema validator (may be null)
* @return CallToolResult with isError=true if validation fails, null if valid or
* validation skipped
*/
public static CallToolResult validate(McpSchema.Tool tool, Map<String, Object> arguments,
boolean validateToolInputs, JsonSchemaValidator validator) {
if (!validateToolInputs || tool.inputSchema() == null || validator == null) {
return null;
}
Map<String, Object> args = arguments != null ? arguments : Map.of();
var validation = validator.validate(tool.inputSchema(), args);
if (!validation.valid()) {
logger.warn("Tool '{}' input validation failed: {}", tool.name(), validation.errorMessage());
return CallToolResult.builder()
.content(List.of(new McpSchema.TextContent(validation.errorMessage())))
.isError(true)
.build();
}
return null;
}
}