MCP Covenant
semver for your MCP server's interface
Snapshots a server's tools/resources/prompts into a lockfile and fails CI on breaking changes, with direction-aware JSON-Schema classification (tightening an input schema vs loosening an output schema break different callers) plus a schema-hygiene linter. Single Rust binary, stdio + HTTP, SARIF + GitHub Action. 132 tests, on crates.io, MIT.
What it solves
When you ship a typed library you have a public API and tooling that screams when you break it. MCP servers have neither. They serve whatever the tool list returns today. Rename a tool, add a required argument, narrow an enum, and every agent built on your server breaks while nothing in your pipeline notices.
How it works
It snapshots the server interface into a lockfile you commit, then compares the live interface against that baseline on every run and classifies each difference the way a person would: breaking, minor or patch. A removed tool and a new required property are breaking, and it says so with the exact path, so the output reads like a review comment rather than a diff. The exit code fails CI and it tells you which version bump the change actually requires.
When to use it
Add it the moment anyone other than you calls your server. From then on the lockfile is the contract, and a breaking change becomes a deliberate decision with a version bump rather than something you find out about from a bug report.
When not to use it
It watches the interface, not the behaviour. A tool that keeps its exact signature and quietly starts returning something different passes every check. It is also only useful once the interface is meant to be stable: during the first weeks of a server, when everything moves, the lockfile is noise.
Stars
★ 0
installs
↓ 18
Clones (14d)
⊟ 36
Language
Rust
Updated
2026-08-21
Install
cargo install mcp-covenant