How to Treat API Contracts as Long-Term Commitments

Breaking clients is breaking trust — version accordingly.

[ essay ]

APIs are promises with semver: additive changes freely, breaking changes only with version bumps and migration windows.

Document error shapes, pagination, idempotency keys, and rate limits as part of the contract — not as footnotes.

Consumers you do not know exist will integrate. Assume external dependency.

Deprecation timelines beat surprise removal. Telemetry on old endpoints tells you when to close.

Promises kept quietly are how platforms age without rage.

— JV · Dark Heart Labs.