# Golang Error Handling

> Standards for error wrapping, checking, and definition in Golang. Use when wrapping errors, defining sentinel errors, or handling errors idiomatically in Go. (triggers: fmt.Errorf, errors.Is, errors.As, error wrapping, sentinel error, error handling)

- Skill: `hoangnguyen0403/golang-error-handling-2` (Agent Skill)
- Install (CLI): `npx skillmds@latest add hoangnguyen0403/golang-error-handling-2`
- Raw SKILL.md: https://api.skillmd.com/api/skills/hoangnguyen0403/golang-error-handling-2/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: HoangNguyen0403 (https://skillmd.com/u/hoangnguyen0403)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/hoangnguyen0403/golang-error-handling-2

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# Golang Error Handling Standards

## **Priority: P0 (CRITICAL)**

## Principles

- **Errors are Values**: Handle them like any other value.
- **Handle Once**: Log OR Return. Never Log AND Return (creates duplicate logs).
- **Add Context**: Don't just return `err` bubble up. Wrap it with context: `fmt.Errorf("failed to open file: %w", err)`.
- **Use Standard Lib**: Go 1.13+ `errors` package (`Is`, `As`, `Unwrap`) is sufficient. Avoid `pkg/errors` (deprecated).

## Guidelines

- **Sentinel Errors**: Expoted, fixed errors (`io.EOF`, `sql.ErrNoRows`). Use `errors.Is(err, io.EOF)`.
- **Error Types**: Structs implementing `error`. Use `errors.As(err, &target)`.
- **Panic**: Only for unrecoverable startup errors.

## Anti-Patterns

- **No bare return err**: Wrap with `fmt.Errorf("context: %w", err)` to preserve call chain.
- **No string error checks**: Use `errors.Is`/`errors.As`; string comparison is brittle.
- **No swallowed errors**: Never assign errors to `_`; always handle or propagate.

## References

- [Error Wrapping Patterns](references/error-wrapping.md)