go-error-handling
Use when writing Go code that returns, wraps, or handles errors — choosing between sentinel errors, custom types, and fmt.Errorf (%w vs %v), structuring error flow, or deciding whether to log or return. Also use when propagating errors across package boundaries or using errors.Is/As, even if the user doesn't ask about error strategy. Does not cover panic/recover patterns (see go-defensive).
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/cxuu/golang-skills --skill go-error-handling- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads go-error-handling automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
Go Error Handling
Compatibility:
errors.Is,errors.As, and%wwrapping require Go 1.13+; structured logging examples may uselog/slogfrom Go 1.21+.
Resource Routing
scripts/check-errors.sh- Run when checking string-based error matching, bare error propagation, and log-and-return patterns.scripts/check-errors-ast.go- Implementation helper invoked bycheck-errors.sh; patch this when changing error-flow analysis behavior.references/ERROR-FLOW.md- Read when deciding where to handle, wrap, log, or return errors.references/ERROR-TYPES.md- Read when choosing sentinel errors, typed errors, or opaque errors.references/WRAPPING.md- Read when choosing%wversus%vor crossing package boundaries.
In Go, errors are values — they are created by code and consumed by code.
Choosing an Error Strategy
- System boundary (RPC, IPC, storage)? → Wrap with
%vto avoid leaking internals - Caller needs to match specific conditions? → Sentinel or typed error, wrap with
%w - Caller just needs debugging context? →
fmt.Errorf("...: %w", err) - Leaf function, no wrapping needed? → Return the error directly
Default: wrap with %w and place it at the end of the format string.
Core Rules
Never Return Concrete Error Types
Never return concrete error types from exported functions — a concrete nil
pointer can become a non-nil interface:
// Bad: Concrete type can cause subtle bugs
func Bad() *os.PathError { /*...*/ }
// Good: Always return the error interface
func Good() error { /*...*/ }
Error Strings
Error strings should not be capitalized and should not end with punctuation. Exception: exported names, proper nouns, or acronyms.
// Bad
err := fmt.Errorf("Something bad happened.")
// Good
err := fmt.Errorf("something bad happened")
For displayed messages (logs, test failures, API responses), capitalization is appropriate.
Return Values on Error
When a function returns an error, callers must treat all non-error return values as unspecified unless explicitly documented.
Tip: Functions taking a context.Context should usually return an error
so callers can determine if the context was cancelled.
Handling Errors
When encountering an error, make a deliberate choice — do not discard
with _:
- Handle immediately — address the error and continue
- Return to caller — optionally wrapped with context
- In exceptional cases —
log.Fatalorpanic
To intentionally ignore: add a comment explaining why.
n, _ := b.Write(p) // never returns a non-nil error
For related concurrent operations, use
errgroup:
g, ctx := errgroup.WithContext(ctx)
g.Go(func() error { return task1(ctx) })
g.Go(func() error { return task2(ctx) })
if err := g.Wait(); err != nil { return err }
Avoid In-Band Errors
Don't return -1, nil, or empty string to signal errors. Use multiple
returns:
// Bad: In-band error value
func Lookup(key string) int // returns -1 for missing
// Good: Explicit error or ok value
func Lookup(key string) (string, bool)
This prevents callers from writing Parse(Lookup(key)) — it causes a
compile-time error since Lookup(key) has 2 outputs.
Error Flow
Handle errors before normal code. Early returns keep the happy path unindented:
// Good: Error first, normal code unindented
if err != nil {
return err
}
// normal code
Handle errors once — either log or return, never both:
Error encountered?
├─ Caller can act on it? → Return (with context via %w)
├─ Top of call chain? → Log and handle
└─ Neither? → Log at appropriate level, continue
Error Types
Advisory: Recommended best practice.
| Caller needs to match? | Message type | Use |
|---|---|---|
| No | static | errors.New("message") |
| No | dynamic | fmt.Errorf("msg: %v", val) |
| Yes | static | var ErrFoo = errors.New("...") |
| Yes | dynamic | custom error type |
Default: Wrap with fmt.Errorf("...: %w", err). Escalate to sentinels for
errors.Is(), to custom types for errors.As().
Error Wrapping
Advisory: Recommended best practice.
- Use
%v: At system boundaries, for logging, to hide internal details - Use
%w: To preserve error chain forerrors.Is/errors.As
Key rules: Place %w at the end. Add context callers don't have. If
annotation adds nothing, return err directly.
Validation: After implementing error handling, run
bash scripts/check-errors.shto detect common anti-patterns. Then rungo vet ./...to catch additional issues.
Related Skills
- Error naming: See go-naming when naming sentinel errors (
ErrFoo) or custom error types - Testing errors: See go-testing when testing error semantics with
errors.Is/errors.Asor writing error-checking helpers - Panic handling: See go-defensive when deciding between panic and error returns, or writing recover guards
- Guard clauses: See go-control-flow when structuring early-return error flow or reducing nesting
- Logging decisions: See go-logging when choosing log levels, configuring structured logging, or deciding what context to include in log messages
FAQ
What does the go-error-handling skill do?
Use when writing Go code that returns, wraps, or handles errors — choosing between sentinel errors, custom types, and fmt.Errorf (%w vs %v), structuring error flow, or deciding whether to log or return. Also use when propagating errors across package boundaries or using errors.Is/As, even if the user doesn't ask about error strategy. Does not cover panic/recover patterns (see go-defensive).
How do I install go-error-handling?
Run npx skills add https://github.com/cxuu/golang-skills --skill go-error-handling in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/go-error-handling/ (personal) or .claude/skills/go-error-handling/ (project).
Which AI agents can use go-error-handling?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is go-error-handling safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains go-error-handling?
It is published by cxuu in cxuu/golang-skills. It has 1,273 recorded installs.
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