JSON Schema validation error with tools.16.custom.input_schema in Cursor 2.0.34

[Qubitix101]

Describe the Bug

Bug Report: JSON Schema Validation Error in Cursor 2.0.34

Issue Summary

Cursor version 2.0.34 is sending built-in tools with invalid JSON schemas to Claude’s API, causing persistent errors that block Claude functionality.

Error Message

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"tools.16.custom.input_schema: JSON schema is invalid. It must match JSON Schema draft 2020-12 (https://json-schema.org/draft/2020-12). Learn more about tool use at https://docs.claude.com/en/docs/tool-use."}}

Also occurs with tools.17.custom.input_schema.

Environment

• OS: macOS
• Cursor Version: 2.0.34
• Claude Extension: Installed and active
• Error Frequency: Every time Claude is used in Cursor

Reproduction Steps

1. Updated Cursor to version 2.0.34
2. Error appears immediately when trying to use Claude in Cursor
3. Disabled ALL MCP servers - error persists
4. Deleted all cache files - error persists
5. Restarted Cursor multiple times - error persists
6. Error occurs with empty MCP configuration (mcpServers: {})

Diagnosis

• All MCP servers disabled - error persists
• All cache files deleted - error persists
• Error occurs with tools at indices 16-17
• Conclusion: These are Cursor’s built-in tools, not MCP tools

The error message indicates tools.16.custom.input_schema and tools.17.custom.input_schema, which suggests Cursor is including custom tools with invalid JSON schemas.

Impact

• Cannot use Claude in Cursor - error blocks all Claude API calls
• Claude works fine in terminal - confirms issue is Cursor-specific
• Workaround: Use Claude in terminal or web interface

Request

Please fix Cursor’s built-in tools (tools 16-17) to comply with JSON Schema draft 2020-12 as required by Claude’s API.

Additional Context

• This started immediately after updating to Cursor 2.0.34
• The error mentions “custom.input_schema” which suggests these are custom tools added by Cursor
• Tools at indices 16-17 are causing the issue
• MCP server configurations are working correctly (tested with all disabled)

---

This is a blocking bug that prevents Claude from working in Cursor.

Steps to Reproduce

by opening terminal and using claude and this error message is reproduced

Operating System

MacOS

Current Cursor Version (Menu → About Cursor → Copy)

Version: 2.0.63
VSCode Version: 1.99.3
Commit: 505046dcfad2acda3d066e32b7cd8b6e2dc1fdc0
Date: 2025-11-05T18:56:58.213Z
Electron: 37.7.0
Chromium: 138.0.7204.251
Node.js: 22.20.0
V8: 13.8.258.32-electron.0
OS: Darwin arm64 25.0.0

Does this stop you from using Cursor

No - Cursor works, but with this issue

[deanrie]

Hey, thanks for the report. This looks like a real issue: Cursor’s built-in tools don’t comply with JSON Schema draft 2020‑12.

To help engineering, please share:

• Request ID: chat menu (top right) > Copy Request ID
• Console logs: Help > Toggle Developer Tools > Console - screenshot errors when reproducing

This will help the team identify which built-in tools are failing schema validation.

[Qubitix101]

“request_id”:“req_011CUsQS5SQs6EfGg1BKMcqb”}

[Qubitix101]

“request_id”:“req_011CUsQmTkcwPpQmg8KtwdBb”}

This is in Terminal

[Qubitix101]

Please come back and help out, not sure how to fix this problem.