mcpkit

Building Model Context Protocol (MCP) servers is difficult because every client—Claude Desktop, ChatGPT, Cursor, VS Code, and others—implements the protocol with unique constraints. A server that works in one environment might silently fail in another due to name truncation, schema depth limits, or handling of structured content.

What it does

• Multi-client validation checks server definitions against known constraints for Claude Desktop, ChatGPT, Cursor, VS Code, Cline, and more.
• Protocol inspection records exactly what the server exposes including tools, resources, and prompts.
• Schema auditing identifies deep nesting or root-level combinators that break specific LLM clients.
• Runtime probing optionally executes tools with readOnlyHint to verify output schema compliance.
• SDK management detects outdated MCP SDKs across Node.js, Python, Go, and Rust and provides precise upgrade commands.
• Transport verification catches stdout pollution that corrupts JSON-RPC messages on stdio transports.

How it works

1. Run npx -y @vrajved/mcpkit -- [start command] to boot the server and perform a full suite of cross-client checks.
2. Review the Markdown report for FAIL and WARN statuses, each containing a specific checkId and a concrete fix.
3. Use the upgrade command to check for SDK updates and optionally apply them if the environment allows.
4. Integrate with CI using the -f github flag to surface protocol violations directly in pull request annotations.

Frameworks & tools

Works with any MCP server regardless of language (Node.js, Python, Go, Rust). Requires Node.js 20+ to run the validator. Supports both stdio and Streamable HTTP transports.

Why this beats prompting it yourself

LLMs often guess at protocol limits or rely on outdated documentation. This tool uses a sourced database of real-world client behaviors to catch silent failures, like name collisions in VS Code or schema stripping in Codex CLI, that simple prompting cannot detect.

Proven on real projects

Run against a live 4-tool MCP server (an LP-solver exposed over MCP) across all 12 supported clients: 0 fails, 0 warnings, 3 informational notes across the whole surface. This is the same validator you'd run against your own server, not a curated example.

Use cases

• Validating a new MCP server before deployment to ensure cross-client compatibility.
• Debugging why tools disappear in specific editors like Cursor or VS Code.
• Verifying that tool results containing structuredContent also provide required text fallbacks.
• Auditing OAuth 2.0 implementations for PKCE S256 compliance required by ChatGPT.

Known limitations

The tool requires a functional build of the server to run. Probing is limited to tools marked as read-only to prevent side effects. Remote servers require reachable URLs and valid headers.