Keep API changes safe for existing clients.
Backward compatibility means a client built against yesterday's contract still works tomorrow. Check that promise before merge instead of discovering the break through support tickets.
Treat the base as the promise
The specification on the base branch represents what current consumers are entitled to depend on.
Evaluate the candidate
The pull-request version is checked for removed behaviour and stricter requirements that an existing consumer cannot satisfy.
Version intentional breaks
When a breaking change is necessary, the failed check provides an explicit decision point for versioning or migration planning.
Protect every pull request automatically
Install the GitHub App, choose a repository and get a clear pass or fail status whenever its OpenAPI contract changes.
Frequently asked questions
What makes an API backward compatible?
A change is backward compatible when clients that worked with the previous contract can continue to send valid requests and understand valid responses.
Is adding an optional field backward compatible?
It is usually an additive, compatible change. Making a previously optional request field required is breaking.
Can I check compatibility online for free?
Yes. Paste or upload the baseline and candidate OpenAPI documents into the free checker on the API Contract Guard homepage.