feat: provide more detailed logs when mcp tool declaration failed.

Author: TomorJM

core/src/main/java/com/google/adk/tools/mcp/AbstractMcpTool.java

@@ -20,6 +20,7 @@
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.google.adk.tools.BaseTool;
+import com.google.adk.tools.mcp.McpToolException.McpToolDeclarationException;
 import com.google.common.collect.ImmutableMap;
 import com.google.genai.types.FunctionDeclaration;
 import io.modelcontextprotocol.spec.McpSchema.CallToolResult;
@@ -77,14 +78,20 @@ public T getMcpSession() {
   @Override
   public Optional<FunctionDeclaration> declaration() {
     JsonSchema schema = this.mcpTool.inputSchema();
-    return Optional.ofNullable(schema)
-        .map(
-            value ->
-                FunctionDeclaration.builder()
-                    .name(this.name())
-                    .description(this.description())
-                    .parametersJsonSchema(value)
-                    .build());
+    try {
+      return Optional.ofNullable(schema)
+          .map(
+              value ->
+                  FunctionDeclaration.builder()
+                      .name(this.name())
+                      .description(this.description())
+                      .parametersJsonSchema(value)
+                      .build());
+    } catch (Exception e) {
+      throw new McpToolDeclarationException(
+          String.format("MCP tool:%s failed to get declaration, schema:%s.", this.name(), schema),
+          e);
+    }
   }
 
   @SuppressWarnings("PreferredInterfaceType") // BaseTool.runAsync() returns Map<String, Object>
@@ -141,4 +148,5 @@ protected static Map<String, Object> wrapCallResult(
     }
     return ImmutableMap.of("text_output", resultMaps);
   }
+
 }

core/src/main/java/com/google/adk/tools/mcp/McpToolException.java

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2025 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.adk.tools.mcp;
+
+/** Base exception for all errors originating from {@code AbstractMcpTool} and its subclasses. */
+public class McpToolException extends RuntimeException {
+
+  public McpToolException(String message, Throwable cause) {
+    super(message, cause);
+  }
+
+  /** Exception thrown when there's an error during MCP tool declaration generated. */
+  public static class McpToolDeclarationException extends McpToolException {
+    public McpToolDeclarationException(String message, Throwable cause) {
+      super(message, cause);
+    }
+  }
+}