Error handling

Skill ComeOnOliver/skillshub/skills/HoangNguyen0403/agent-skills-standard/error-handling

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Cross-cutting standards for error design, response shapes, error codes, and boundary placement. Use when handling errors, designing exception flows, or standardizing error responses.

SKILL.md

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Common Error Handling Standards

Priority: P1 (OPERATIONAL)

Consistent, predictable error handling is the backbone of maintainable systems. Errors are first-class citizens — design them explicitly.

🏗 Error Response Shape (HTTP APIs)

All API errors MUST use a consistent envelope:

{
  "error": {
    "code": "USER_NOT_FOUND",
    "message": "The requested user does not exist.",
    "traceId": "4bf92f3577b34da6a3ce929d0e0e4736",
    "details": []
  }
}

Field	Rule
`code`	SCREAMING_SNAKE_CASE machine-readable code. Never localize.
`message`	Human-readable English summary. Safe for end-users (no stack traces).
`traceId`	Correlation ID from the request context.
`details`	Optional array of field-level validation errors. Empty for non-validation errors.

🗂 Error Classification

Layer	Error Type	Strategy
Validation	`400 Bad Request`	Return `details[]` with field paths
Authentication	`401 Unauthorized`	Generic message — never expose reason
Authorization	`403 Forbidden`	Log attempt, never expose role info
Not Found	`404 Not Found`	Distinguishable from auth errors
Conflict	`409 Conflict`	Include conflicting resource ID
Unhandled	`500 Internal Server Error`	Log full context, return generic message

📦 Error Wrapping vs Replacement

Wrap when adding context: fmt.Errorf("processOrder: %w", err) (Go) / new ServiceError('msg', { cause: err }) (JS).
Replace only when the original error leaks sensitive internal details.
Never swallow: Catch without logging or re-throwing hides bugs — forbidden.

🛡 Boundary Placement

API Layer: Translate domain/infrastructure errors into HTTP responses. Use a global exception filter/middleware.
Domain Layer: Throw domain-specific errors (e.g., InsufficientStockError). Never reference HTTP status codes.
Infrastructure Layer: Throw infrastructure errors (e.g., DatabaseConnectionError). Wrap 3rd party exceptions.
Never: Let infrastructure errors (raw DB/network exceptions) bubble up to the API response.

Request → [API Layer: maps to HTTP] → [Domain: business errors] → [Infra: DB/network errors]

🔢 Error Code Design

Codes are permanent IDs — treat them like API contracts. Once published, never rename.
Format: <DOMAIN>_<NOUN>_<VERB> → ORDER_PAYMENT_FAILED, USER_EMAIL_DUPLICATE.
Define in a centralized constants file; never inline magic strings.

Anti-Patterns

No catch(e) {}: Always log or re-throw.
No stack traces in responses: Leak internal structure to attackers.
No generic 500 for validation: Use 400 with details.
No HTTP status codes in domain layer: Domain errors are business concepts, not transport decisions.
No error-code proliferation: Prefer a small, well-documented set over one code per exception class.