Error Codes

Error Codes (TT-xxx)

All API errors are normalized into a consistent shape by the GlobalExceptionFilter. Clients never see raw NestJS/Prisma errors — they receive a structured payload:

{
  "code": "TT-401",
  "message": "Ungültige Anmeldedaten",
  "locale": "de",
  "details": "…"
}

How it works

1. Error codes are declared centrally in packages/shared/src/errors/codes.ts.
2. Services throw specific error classes (e.g. NotFoundException, domain errors) instead of generic Errors.
3. The GlobalExceptionFilter maps exceptions → TT-xxx code + localized message + HTTP status.
4. The frontend maps codes to localized UI messages via the shared package — the same catalog on both sides.

Rules

• New error codes go in codes.ts — never hardcode message strings or ad-hoc codes in modules.
• Throw specific error classes so the filter can map them correctly.
• Test with specific classes: expect(fn).rejects.toThrow(ConflictException) — not generic toThrow().
• Keep error messages free of sensitive data (no emails, internal IDs, stack details) — responses are shown to end users.

Response shape

Field	Meaning
code	Stable machine-readable code (TT-xxx)
message	Localized, user-facing message
locale	Resolved request locale
details	Optional technical hint (safe subset)