refactor: reduce log verbosity by adjusting log levels

- Change most INFO logs to DEBUG level for operational messages
- Keep stderr messages at INFO level
- Rename errorHandler to stdErrorHandler in StdioClientTransport
- Add debug logging for JSON message deserialization

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>

mcp-spring/mcp-spring-webflux/src/main/java/io/modelcontextprotocol/server/transport/WebFluxSseServerTransport.java

@@ -251,7 +251,7 @@ public class WebFluxSseServerTransport implements ServerMcpTransport {
 				.then(Mono.fromRunnable(() -> sessions.remove(sessionId)));
 		}).toList()))
 			.timeout(Duration.ofSeconds(5))
-			.doOnSuccess(v -> logger.info("Graceful shutdown completed"))
+			.doOnSuccess(v -> logger.debug("Graceful shutdown completed"))
 			.doOnError(e -> logger.error("Error during graceful shutdown: {}", e.getMessage()));
 	}
 

mcp-spring/mcp-spring-webmvc/src/main/java/io/modelcontextprotocol/server/transport/WebMvcSseServerTransport.java

@@ -353,7 +353,7 @@ public class WebMvcSseServerTransport implements ServerMcpTransport {
 				sessions.remove(sessionId);
 			});
 
-			logger.info("Graceful shutdown completed");
+			logger.debug("Graceful shutdown completed");
 		});
 	}
 

mcp/src/main/java/io/modelcontextprotocol/client/McpAsyncClient.java

@@ -173,7 +173,7 @@ public class McpAsyncClient {
 		// Tools Change Notification
 		List<Function<List<McpSchema.Tool>, Mono<Void>>> toolsChangeConsumersFinal = new ArrayList<>();
 		toolsChangeConsumersFinal
-			.add((notification) -> Mono.fromRunnable(() -> logger.info("Tools changed: {}", notification)));
+			.add((notification) -> Mono.fromRunnable(() -> logger.debug("Tools changed: {}", notification)));
 
 		if (!Utils.isEmpty(features.toolsChangeConsumers())) {
 			toolsChangeConsumersFinal.addAll(features.toolsChangeConsumers());
@@ -184,7 +184,7 @@ public class McpAsyncClient {
 		// Resources Change Notification
 		List<Function<List<McpSchema.Resource>, Mono<Void>>> resourcesChangeConsumersFinal = new ArrayList<>();
 		resourcesChangeConsumersFinal
-			.add((notification) -> Mono.fromRunnable(() -> logger.info("Resources changed: {}", notification)));
+			.add((notification) -> Mono.fromRunnable(() -> logger.debug("Resources changed: {}", notification)));
 
 		if (!Utils.isEmpty(features.resourcesChangeConsumers())) {
 			resourcesChangeConsumersFinal.addAll(features.resourcesChangeConsumers());
@@ -196,7 +196,7 @@ public class McpAsyncClient {
 		// Prompts Change Notification
 		List<Function<List<McpSchema.Prompt>, Mono<Void>>> promptsChangeConsumersFinal = new ArrayList<>();
 		promptsChangeConsumersFinal
-			.add((notification) -> Mono.fromRunnable(() -> logger.info("Prompts changed: {}", notification)));
+			.add((notification) -> Mono.fromRunnable(() -> logger.debug("Prompts changed: {}", notification)));
 		if (!Utils.isEmpty(features.promptsChangeConsumers())) {
 			promptsChangeConsumersFinal.addAll(features.promptsChangeConsumers());
 		}
@@ -205,7 +205,7 @@ public class McpAsyncClient {
 
 		// Utility Logging Notification
 		List<Function<LoggingMessageNotification, Mono<Void>>> loggingConsumersFinal = new ArrayList<>();
-		loggingConsumersFinal.add((notification) -> Mono.fromRunnable(() -> logger.info("Logging: {}", notification)));
+		loggingConsumersFinal.add((notification) -> Mono.fromRunnable(() -> logger.debug("Logging: {}", notification)));
 		if (!Utils.isEmpty(features.loggingConsumers())) {
 			loggingConsumersFinal.addAll(features.loggingConsumers());
 		}
@@ -364,7 +364,7 @@ public class McpAsyncClient {
 
 		this.roots.put(root.uri(), root);
 
-		logger.info("Added root: {}", root);
+		logger.debug("Added root: {}", root);
 
 		if (this.clientCapabilities.roots().listChanged()) {
 			return this.rootsListChangedNotification();
@@ -390,7 +390,7 @@ public class McpAsyncClient {
 		Root removed = this.roots.remove(rootUri);
 
 		if (removed != null) {
-			logger.info("Removed Root: {}", rootUri);
+			logger.debug("Removed Root: {}", rootUri);
 			if (this.clientCapabilities.roots().listChanged()) {
 				return this.rootsListChangedNotification();
 			}

mcp/src/main/java/io/modelcontextprotocol/client/transport/StdioClientTransport.java

@@ -68,7 +68,7 @@ public class StdioClientTransport implements ClientMcpTransport {
 	private volatile boolean isClosing = false;
 
 	// visible for tests
-	private Consumer<String> errorHandler = error -> logger.error("Error received: {}", error);
+	private Consumer<String> stdErrorHandler = error -> logger.info("STDERR Message received: {}", error);
 
 	/**
 	 * Creates a new StdioClientTransport with the specified parameters and default
@@ -164,8 +164,8 @@ public class StdioClientTransport implements ClientMcpTransport {
 	 * </p>
 	 * @param errorHandler a consumer that processes error messages
 	 */
-	public void setErrorHandler(Consumer<String> errorHandler) {
+	public void setStdErrorHandler(Consumer<String> errorHandler) {
-		this.errorHandler = errorHandler;
+		this.stdErrorHandler = errorHandler;
 	}
 
 	/**
@@ -192,7 +192,6 @@ public class StdioClientTransport implements ClientMcpTransport {
 				String line;
 				while (!isClosing && (line = processErrorReader.readLine()) != null) {
 					try {
-						logger.error("Received error line: {}", line);
 						if (!this.errorSink.tryEmitNext(line).isSuccess()) {
 							if (!isClosing) {
 								logger.error("Failed to emit error message");
@@ -230,7 +229,7 @@ public class StdioClientTransport implements ClientMcpTransport {
 
 	private void handleIncomingErrors() {
 		this.errorSink.asFlux().subscribe(e -> {
-			this.errorHandler.accept(e);
+			this.stdErrorHandler.accept(e);
 		});
 	}
 
@@ -355,7 +354,7 @@ public class StdioClientTransport implements ClientMcpTransport {
 			// Give a short time for any pending messages to be processed
 			return Mono.delay(Duration.ofMillis(100));
 		})).then(Mono.fromFuture(() -> {
-			logger.info("Sending TERM to process");
+			logger.debug("Sending TERM to process");
 			if (this.process != null) {
 				this.process.destroy();
 				return process.onExit();
@@ -375,7 +374,7 @@ public class StdioClientTransport implements ClientMcpTransport {
 				errorScheduler.dispose();
 				outboundScheduler.dispose();
 
-				logger.info("Graceful shutdown completed");
+				logger.debug("Graceful shutdown completed");
 			}
 			catch (Exception e) {
 				logger.error("Error during graceful shutdown", e);

mcp/src/main/java/io/modelcontextprotocol/server/McpAsyncServer.java

@@ -318,7 +318,7 @@ public class McpAsyncServer {
 			}
 
 			this.tools.add(toolRegistration);
-			logger.info("Added tool handler: {}", toolRegistration.tool().name());
+			logger.debug("Added tool handler: {}", toolRegistration.tool().name());
 
 			if (this.serverCapabilities.tools().listChanged()) {
 				return notifyToolsListChanged();
@@ -343,7 +343,7 @@ public class McpAsyncServer {
 		return Mono.defer(() -> {
 			boolean removed = this.tools.removeIf(toolRegistration -> toolRegistration.tool().name().equals(toolName));
 			if (removed) {
-				logger.info("Removed tool handler: {}", toolName);
+				logger.debug("Removed tool handler: {}", toolName);
 				if (this.serverCapabilities.tools().listChanged()) {
 					return notifyToolsListChanged();
 				}
@@ -411,7 +411,7 @@ public class McpAsyncServer {
 				return Mono
 					.error(new McpError("Resource with URI '" + resourceHandler.resource().uri() + "' already exists"));
 			}
-			logger.info("Added resource handler: {}", resourceHandler.resource().uri());
+			logger.debug("Added resource handler: {}", resourceHandler.resource().uri());
 			if (this.serverCapabilities.resources().listChanged()) {
 				return notifyResourcesListChanged();
 			}
@@ -435,7 +435,7 @@ public class McpAsyncServer {
 		return Mono.defer(() -> {
 			McpServerFeatures.AsyncResourceRegistration removed = this.resources.remove(resourceUri);
 			if (removed != null) {
-				logger.info("Removed resource handler: {}", resourceUri);
+				logger.debug("Removed resource handler: {}", resourceUri);
 				if (this.serverCapabilities.resources().listChanged()) {
 					return notifyResourcesListChanged();
 				}
@@ -507,7 +507,7 @@ public class McpAsyncServer {
 						new McpError("Prompt with name '" + promptRegistration.prompt().name() + "' already exists"));
 			}
 
-			logger.info("Added prompt handler: {}", promptRegistration.prompt().name());
+			logger.debug("Added prompt handler: {}", promptRegistration.prompt().name());
 
 			// Servers that declared the listChanged capability SHOULD send a
 			// notification,
@@ -536,7 +536,7 @@ public class McpAsyncServer {
 			McpServerFeatures.AsyncPromptRegistration removed = this.prompts.remove(promptName);
 
 			if (removed != null) {
-				logger.info("Removed prompt handler: {}", promptName);
+				logger.debug("Removed prompt handler: {}", promptName);
 				// Servers that declared the listChanged capability SHOULD send a
 				// notification, when the list of available prompts changes
 				if (this.serverCapabilities.prompts().listChanged()) {

mcp/src/main/java/io/modelcontextprotocol/server/transport/StdioServerTransport.java

@@ -141,6 +141,8 @@ public class StdioServerTransport implements ServerMcpTransport {
 							break;
 						}
 
+						logger.debug("Received JSON message: {}", line);
+
 						try {
 							JSONRPCMessage message = McpSchema.deserializeJsonRpcMessage(this.objectMapper, line);
 							if (!this.inboundSink.tryEmitNext(message).isSuccess()) {
@@ -229,7 +231,7 @@ public class StdioServerTransport implements ServerMcpTransport {
 			// Completing the inbound causes the outbound to be completed as well, so
 			// we only close the inbound.
 			inboundSink.tryEmitComplete();
-			logger.info("Graceful shutdown complete");
+			logger.debug("Graceful shutdown complete");
 			return Mono.empty();
 		}).subscribeOn(Schedulers.boundedElastic());
 	}

mcp/src/main/java/io/modelcontextprotocol/spec/DefaultMcpSession.java

@@ -124,7 +124,7 @@ public class DefaultMcpSession implements McpSession {
 		// consumer
 		this.connection = this.transport.connect(mono -> mono.doOnNext(message -> {
 			if (message instanceof McpSchema.JSONRPCResponse response) {
-				logger.info("Received Response: {}", response);
+				logger.debug("Received Response: {}", response);
 				var sink = pendingResponses.remove(response.id());
 				if (sink == null) {
 					logger.warn("Unexpected response for unkown id {}", response.id());
@@ -134,7 +134,7 @@ public class DefaultMcpSession implements McpSession {
 				}
 			}
 			else if (message instanceof McpSchema.JSONRPCRequest request) {
-				logger.info("Received request: {}", request);
+				logger.debug("Received request: {}", request);
 				handleIncomingRequest(request).subscribe(response -> transport.sendMessage(response).subscribe(),
 						error -> {
 							var errorResponse = new McpSchema.JSONRPCResponse(McpSchema.JSONRPC_VERSION, request.id(),
@@ -144,7 +144,7 @@ public class DefaultMcpSession implements McpSession {
 						});
 			}
 			else if (message instanceof McpSchema.JSONRPCNotification notification) {
-				logger.info("Received notification: {}", notification);
+				logger.debug("Received notification: {}", notification);
 				handleIncomingNotification(notification).subscribe(null,
 						error -> logger.error("Error handling notification: {}", error.getMessage()));
 			}

mcp/src/main/java/io/modelcontextprotocol/spec/McpSchema.java

@@ -17,6 +17,8 @@ import com.fasterxml.jackson.annotation.JsonTypeInfo;
 import com.fasterxml.jackson.annotation.JsonTypeInfo.As;
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * Based on the <a href="http://www.jsonrpc.org/specification">JSON-RPC 2.0
@@ -28,6 +30,8 @@ import com.fasterxml.jackson.databind.ObjectMapper;
  */
 public final class McpSchema {
 
+	private static final Logger logger = LoggerFactory.getLogger(McpSchema.class);
+
 	private McpSchema() {
 	}
 
@@ -144,6 +148,8 @@ public final class McpSchema {
 	public static JSONRPCMessage deserializeJsonRpcMessage(ObjectMapper objectMapper, String jsonText)
 			throws IOException {
 
+		logger.debug("Received JSON message: {}", jsonText);
+
 		var map = objectMapper.readValue(jsonText, MAP_TYPE_REF);
 
 		// Determine message type based on specific JSON structure

mcp/src/test/java/io/modelcontextprotocol/client/StdioMcpSyncClientTests.java

@@ -36,7 +36,7 @@ class StdioMcpSyncClientTests extends AbstractMcpSyncClientTests {
 	void customErrorHandlerShouldReceiveErrors() {
 		AtomicReference<String> receivedError = new AtomicReference<>();
 
-		((StdioClientTransport) mcpTransport).setErrorHandler(error -> receivedError.set(error));
+		((StdioClientTransport) mcpTransport).setStdErrorHandler(error -> receivedError.set(error));
 
 		String errorMessage = "Test error";
 		((StdioClientTransport) mcpTransport).getErrorSink().tryEmitNext(errorMessage);