# Review API error handling as part of the user contract

Canonical: https://githtml.com/guides/review-api-error-handling
Published: 2026-09-26
Publisher: WaveTech LLC / gitHtml

Error handling is part of an API's contract, not merely a logging detail. Review how failures are classified, what the client receives, which actions are safe to retry, and what information remains private. Compare the documented behavior with implementation and tests, especially where several internal failures become the same public response.

## Trace one failure from cause to response

Choose an illustrative invalid export request and follow validation, internal error representation, transport status, response body, and user-facing interpretation. Then contrast a temporary dependency failure. These cases may deserve different recovery behavior even if they share a broad internal exception type. RFC 9457 defines a format for problem details in HTTP APIs, but a project must actually adopt it before documentation can promise those fields. State the reviewed API version and avoid assuming a standard-shaped example proves conformance.

## Check what the client can safely infer

Ask whether callers can distinguish invalid input, lack of permission, missing resources, and temporary unavailability according to the actual contract. Inspect whether error messages reveal sensitive details such as internal paths or personal data. Review retry guidance carefully: repeating a request may have effects, especially when the original outcome is unknown. HTTP semantics provide useful background, but the application's operation and idempotency behavior need their own evidence. An illustrative timeout review should ask whether the server may already have completed the requested work.

1. Classification: identify the failure category and public status or code.
2. Recovery: document the supported client action and any retry condition.
3. Disclosure: ensure public details help users without exposing internal secrets.

## Review negative tests and documentation together

Find tests for important error cases and read their assertions, not just the names. A test that expects any failure does not establish the documented response fields. Compare examples with the contract and label fictional values clearly. Capture mismatches as actionable questions or findings with source references. In a mobile HTML packet, place each error case in a short section with its trigger, response, and client consequence. Keep raw traces out of the public example unless they have been reviewed and redacted; the reader needs the contract, not every internal diagnostic.

## Sources and further reading

- [RFC 9457: Problem Details for HTTP APIs](https://www.rfc-editor.org/rfc/rfc9457.html)
- [RFC 9110: HTTP Semantics](https://datatracker.ietf.org/doc/html/rfc9110)

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