René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Tool input validation returns with misleading error referencing `outputSchema`","articleBody":"**Bug description**\n\nThe tool input validation introduced in https://github.com/modelcontextprotocol/java-sdk/pull/873 returns with a misleading error message referencing `outputSchema` when validation fails. For example, the first test case in \n[ToolInputValidationIntegrationTests#invalidInput_withDefaultValidation_shouldReturnToolError](https://github.com/modelcontextprotocol/java-sdk/blob/c8ab3411b9191ffbbb30f0baaa56b3a26e076dbe/mcp-test/src/test/java/io/modelcontextprotocol/server/ToolInputValidationIntegrationTests.java#L174) leads to the following error message, but only tests for the presence of `age` in the error message substring:\n\n```\nValidation failed: structuredContent does not match tool outputSchema. Validation errors: [: required property 'age' not found]\n```\n\nInstead of referring to `structuredContent` and `outputSchema`, the error message should clearly indicate that the error is referring to the input data as otherwise it's misleading to consumers/LLMs.\n\n**Environment**\n\nMCP SDK 2.0.0-M3 (via Spring AI 2.0.0-M7)\n\n**Steps to reproduce**\n\n- Run `ToolInputValidationIntegrationTests#invalidInput_withDefaultValidation_shouldReturnToolError` \u0026 inspect the produced error message.\n- or create an MCP server with tool input validation enabled and call a tool with invalid input data\n\n**Expected behavior**\n\n- A concise error response stating that the listed schema validation errors refer to input parameters.\n- Better assertions in the tool input validation test, not only checking for presence of a substring.\n\n\n**Minimal Complete Reproducible example**\n\nSee steps to reproduce.\n","author":{"url":"https://github.com/maff","@type":"Person","name":"maff"},"datePublished":"2026-05-28T06:18:25.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/986/java-sdk/issues/986"}