Briefle words · Code & architecture
Error code
A short, stable, machine-readable label for a specific kind of failure that programs can check, separate from the human-readable message.
Say it to an AI
When POST /v1/bookings fails payment, return a Problem Details (RFC 9457) body: type, title, status and a human detail, plus a stable machine-readable error code (e.g. card_expired), the offending field and the correlation ID. Never a generic 'Something went wrong'.
How an expert would brief the stronger version of “Booking API error”.
See it
Try it as a puzzle →An API client showing what a travel booking API returns when the payment step fails.
Why: B's '"code": "card_expired"' lets the app show a 'use another card' screen; A's only clue is the free-text 'Something went wrong'.
More ways experts use it
Add one error-handling middleware for the payments API so every endpoint returns the same error envelope: {"error": {"code", "message", "field?"}} with a stable snake_case error code and the right 4xx status. Route handlers throw typed errors; only the middleware formats responses.
Payment API errors · Code & architecture
Related words
Room 1 · Essentials
Learn “Error code” in a five-minute lesson