A client receives an error, but the body contains only “Something went wrong.” The HTTP status may identify a broad category, while the client still lacks enough information to react usefully. API error responses deserve a documented contract alongside the successful result.
That contract helps application developers decide whether to show a message, ask the user to correct input, retry through an approved policy or stop. It should not expose internal details merely to make debugging easier.
Separate the status from the specific problem
A status and a response body serve related but different purposes. For a sample validation failure, the client may need to know which submitted field requires correction. A missing-resource response may need a stable problem identifier that code can handle without comparing an English sentence.
RFC 9457 defines a standard problem-details representation for machine-readable HTTP API errors. If your API uses it, follow its defined members and semantics. If it uses another format, document that format rather than pretending every service shares the same field names.
Keep client decisions tied to stable documented values. Human-readable wording can change for clarity or localization. A client that treats an exact sentence as an error code can break when the message improves.
Show the cases that require different actions
Provide safe examples for the failures the integration must handle. Missing input, an unavailable resource and a temporary service failure can require different responses. Do not infer a retry rule from one example or assume every failure should trigger another immediate request.
Document the actual retry and rate-limit behavior where it applies. A contract should explain what the client is permitted to do, while the implementation needs its own appropriate tests.
JSON Formatter can help inspect supported example payloads. It checks their syntax and makes their structure easier to read. It does not establish that an error code belongs to the correct HTTP status or that the client will react appropriately.
Keep internal debugging details in the right place
Avoid turning stack traces, credentials or unnecessary personal data into public error content. Use the approved diagnostic process for the internal details. If the response includes a support reference, document its purpose without making it a secret access token.
JSON to TypeScript can provide a starting model for supplied error samples. Review the generated output against the documented variants. One sample cannot establish every optional field or response case, and generated models do not automatically validate incoming data at runtime.
Before accepting the integration, review one ordinary failure and one less common permitted case through an authorized test workflow. Check what the user sees and what the application does next. A useful error contract turns a failed request into an understandable outcome without disclosing more than the recipient needs.