# go-error-handling

Guides coding agents on idiomatic Go error handling, covering sentinel errors, error wrapping with %w or %v, and clean error flow.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 1300 installs · ★ 181
- Author: cxuu
- License: Apache-2.0 · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/cxuu/golang-skills/tree/HEAD/skills/go-error-handling/SKILL.md
- Updated: 2026-06-20
- HTML: https://affpapa.org/en/nevibecode/skills/go-error-handling

## What it does

The skill enforces explicit error handling patterns in Go. It stops agents from returning concrete error pointer types from exported functions, which prevents nil-interface bugs. It also bars in-band error returns like `-1` or empty strings, requiring lowercase error strings without trailing punctuation.

It structures the choice of error strategy: use `%v` at external boundaries to hide implementation details, and use `%w` when callers need inspection via `errors.Is` or `errors.As`. To catch issues automatically, the package bundles `scripts/check-errors.sh` and `scripts/check-errors-ast.go` to scan AST code for string-based error matching or log-and-return anti-patterns.

Error unwrapping rules require Go 1.13+, and structured logging examples rely on `log/slog` from Go 1.21+. The skill intentionally omits `panic` and `recover` logic, leaving defensive guards to the separate `go-defensive` skill.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add cxuu/golang-skills --skill go-error-handling -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/go-error-handling/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/go-error-handling/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add cxuu/golang-skills --skill go-error-handling -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/go-error-handling/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add cxuu/golang-skills --skill go-error-handling -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/go-error-handling/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install cxuu/golang-skills go-error-handling
```

2. **Manually: put the files in place**
- File: `.github/skills/go-error-handling/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add cxuu/golang-skills --skill go-error-handling -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/cxuu/golang-skills --path skills/go-error-handling
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/go-error-handling/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add cxuu/golang-skills --skill go-error-handling -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/cxuu/golang-skills/tree/HEAD/skills/go-error-handling/SKILL.md

## When to use it
- choose between `%w` and `%v` when wrapping errors across boundaries
- eliminate log-and-return anti-patterns across call chains
- prevent concrete error pointer nil-interface bugs in exported APIs
- coordinate concurrent worker failures using `errgroup`

## Example prompts
- Review this Go package for log-and-return anti-patterns and fix them.
- Refactor this service method to return custom sentinel errors compatible with errors.Is.
- Run scripts/check-errors.sh to inspect our Go error handling logic.

## Source text · SKILL.md · Apache-2.0

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: af5e82a08b0664e5.

BEGIN THIRD-PARTY FILE af5e82a08b0664e5
````text
---
name: go-error-handling
description: 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).
allowed-tools: Bash(bash:*)
---

# Go Error Handling

> Compatibility: `errors.Is`, `errors.As`, and `%w` wrapping require Go 1.13+; structured logging examples may use `log/slog` from 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 by `check-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 `%w` versus `%v` or crossing package boundaries.

In Go, [errors are values](https://go.dev/blog/errors-are-values) — they are
created by code and consumed by code.

## Choosing an Error Strategy

1. System boundary (RPC, IPC, storage)? → Wrap with `%v` to avoid leaking internals
2. Caller needs to match specific conditions? → Sentinel or typed error, wrap with `%w`
3. Caller just needs debugging context? → `fmt.Errorf("...: %w", err)`
4. 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:

```go
// 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.

```go
// 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
````
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First 2792 of 6045 bytes. © cxuu · Apache-2.0 · https://github.com/cxuu/golang-skills/tree/HEAD/skills/go-error-handling/SKILL.md

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