mcp-recorder – VCR.py for MCP servers. Record, replay, verify
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…
mcp-recorder – VCR.py for MCP servers. Record, replay, verify launched on March 6, 2026 with 6 votes, #1,631 of 23,380 launches that month and more than 75% of that year's launches.
What it does
A lightweight proxy that records and replays MCP server interactions for deterministic testing and CI-friendly regression workflows. - devhelmhq/mcp-recorder
In the maker’s words, at launch
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…
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MCP-Shield – Detect security issues in MCP servers2025 · github.com · ▲134I noticed the growing security concerns around MCP (https://news.ycombinator.com/item?id=43600192) and built an open source tool that can detect several patterns of tool poisoning attacks, exfiltration channels and cross-origin manipulations. MCP-Shield scans your installed servers (Cursor, Claude Desktop, etc.) and shows what each tool is trying to do at the instruction level, beyond just the API surface. It catches hidden instructions that try to read sensitive files, shadow other tools' behavior, or exfiltrate data. Example of what it detects: - Hidden instructions…
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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…
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