MCPSpec – Ship reliable MCP servers without writing test code
Hi HN, I've been building MCPSpec, an open-source CLI for MCP server reliability. Record sessions, generate mock servers, catch Tool Poisoning, and fail your CI build when something's wrong — without writing test code. There are ways to validate MCP servers today — the MCP Inspector, ad-hoc SDK scripts, unit tests for server internals — but nothing that handles regression detection, security auditing, mock generation, and CI pass/fail checks in one tool. MCPSpec does that: 1. Record a session against your real server, replay it after changes to catch regressions 2. Generate a standalone…
What it does
In the maker’s words, at launch
Hi HN, I've been building MCPSpec, an open-source CLI for MCP server reliability. Record sessions, generate mock servers, catch Tool Poisoning, and fail your CI build when something's wrong — without writing test code. There are ways to validate MCP servers today — the MCP Inspector, ad-hoc SDK scripts, unit tests for server internals — but nothing that handles regression detection, security auditing, mock generation, and CI pass/fail checks in one tool. MCPSpec does that: 1. Record a session against your real server, replay it after changes to catch regressions 2. Generate a standalone .js mock from any recording — no API keys, no live server needed in CI 3. Security audit with 8 rules including Tool Poisoning (prompt injection hidden in tool descriptions) 4. 0-100 quality score across documentation, schema quality, error handling, responsiveness, and security 5. One command to generate GitHub Actions / GitLab CI configs No LLMs in the loop. Deterministic and fast. Ships with 70 ready-to-run tests for 7 popular MCP servers. GitHub: https://github.com/light-handle/mcpspec Docs: https://light-handle.github.io/mcpspec/ Would love feedback or feature ideas.
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Hi HN, I'm Vlad. I've been building MCP servers and related tooling for a while now, and I kept hitting a class of bug that no unit test caught: someone on the team renames a tool parameter or tweaks a tool description, all the tests pass, but the AI agent that was calling that tool silently breaks. This happens because the model reads tool descriptions and parameter schemas to decide which tool to call and how, so a renamed parameter or a reworded description isn't just a cosmetic change — it directly affects the model's behavior. The MCP spec doesn't have tool versioning available yet, and…
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