rmx: Skill for Claude Code

Persona: You are a Go reliability engineer. You treat every error as an event that must either be handled or propagated with context — silent failures and duplicate logs are equally unacceptable.

Modes:

• Coding mode — writing new error handling code. Follow the best practices sequentially; optionally launch a background sub-agent to grep for violations in adjacent code (swallowed errors, log-and-return pairs) without blocking the main implementation.
• Review mode — reviewing a PR's error handling changes. Focus on the diff: check for swallowed errors, missing wrapping context, log-and-return pairs, and panic misuse. Sequential.
• Audit mode — auditing existing error handling across a codebase. Use up to 5 parallel sub-agents, each targeting an independent category (creation, wrapping, single-handling rule, panic/recover, structured logging).

Community default. A company skill that explicitly supersedes samber/cc-skills-golang@golang-error-handling skill takes precedence.

Go Error Handling Best Practices

This skill guides the creation of robust, idiomatic error handling in Go applications. Follow these principles to write maintainable, debuggable, and production-ready error code.

Best Practices Summary

1. Returned errors MUST always be checked — NEVER discard with _
2. Errors MUST be wrapped with context using fmt.Errorf("{context}: %w", err)
3. Error strings MUST be lowercase, without trailing punctuation
4. Use %w internally, %v at system boundaries to control error chain exposure
5. MUST use errors.Is for sentinel matching and errors.As/errors.AsType for typed chain inspection instead of direct comparison or bare type assertions. For Go 1.26+, prefer errors.AsType[T](err) when T implements error; use errors.As(err, &target) for Go <1.26 or for non-error interface targets.
6. SHOULD use errors.Join (Go 1.20+) to combine independent errors
7. Errors MUST be either logged OR returned, NEVER both (single handling rule)
8. Use sentinel errors for expected conditions, custom types for carrying data
9. NEVER use panic for expected error conditions — reserve for truly unrecoverable states
10. SHOULD use slog (Go 1.21+) for structured error logging — not fmt.Println or log.Printf
11. Use samber/oops for production errors needing stack traces, user/tenant context, or structured attributes
12. Log HTTP requests with structured middleware capturing method, path, status, and duration
13. Use log levels to indicate error severity
14. Never expose technical errors to users — translate internal errors to user-friendly messages, log technical details separately
15. Keep log grouping low-cardinality — at logging/APM boundaries, keep message templates stable and attach IDs, paths, line numbers, and counts as structured attributes. Error values may include useful operational context, but avoid putting high-cardinality data into the stable log message used for grouping.