MCP Server Interface Diff Tool

Summary

@SamMorrowDrums has built an MCP server diff tool that compares the public interfaces of MCP servers from a client's perspective. He's proposing potential integration into the Inspector CLI as a sub-command.

The Tool

• Repository: https://github.com/SamMorrowDrums/mcp-server-diff
• NPM package: npx mcp-server-diff@latest
• Supports comparing stdio and remote MCP servers
• Outputs diffs of tools, prompts, resources, and resource templates

Use Cases

1. Catching regressions during refactors - Architecture refactors and SDK changes shouldn't cause schema diffs. This has caught mistakes in refactors and would have prevented a breaking client issue caused by an OpenAI strict mode regression (SDK upgrade removed a schema fix).

2. Version comparison - See concrete schema differences between two versions of the same server, or what user-facing changes a fork has made.

3. Cross-language consistency - Sam uses it to reduce diffs between 7 repos in different languages meant to provide the same server interface. Makes it easy to get agents to fix or reduce differences.

4. SDK compliance testing - Interest expressed in using it with the everything server to clearly see client-facing changes for SDK compliance validation.

5. PR review - Useful output for reviewing PRs that add tools or modify server interfaces.

6. Toolset/mode validation - In GitHub MCP, used to check multiple toolsets and modes aren't accidentally impacted or changed.

Examples

• [GitHub Action report with diff](https://github.com/SamMorrowDrums/mcp-go-starter/actions/runs/21102867696)
• [Cross-repo comparison issue](https://github.com/SamMorrowDrums/mcp-starters/issues/3) - Compares 7 mcp-<lang>-starter repos against Python as reference implementation

Open Questions

• Should this live as a separate project or be bundled into Inspector?
• May be worth seeing adoption before considering bundling
• May also be a plugin?

Additional Context

Discord threads:

• https://discord.com/channels/1358869848138059966/1435401076265324554/1463469569246101570
• https://discord.com/channels/1358869848138059966/1435401076265324554/1463472822793015387

Start by reviewing the Inspector CLI and the proposed mcp-server-diff repository, invoked with npx mcp-server-diff@latest. The issue leaves project placement, plugin versus sub-command design, and acceptance criteria open; done would require an agreed integration approach and verified interface-diff behavior.