go-documentation

---
name: go-documentation
description: Use when writing or reviewing documentation for Go packages, types, functions, or methods. Also use proactively when creating new exported types, functions, or packages, even if the user doesn't explicitly ask about documentation. Does not cover code comments for non-exported symbols (see go-style-core).
license: Apache-2.0
---

# Go Documentation

## Resource Routing

- `scripts/check-docs.sh` - Run when checking exported functions, types, methods, constants, and packages for missing doc comments.
- `scripts/check-docs-ast.go` - Implementation helper invoked by `check-docs.sh`; patch this when changing documentation analysis behavior.
- `assets/doc-template.go` - Use when starting a documented package or exported API.
- `references/CONVENTIONS.md` - Read when documenting parameters, context behavior, concurrency safety, cleanup, errors, or named results.
- `references/EXAMPLES.md` - Read when adding runnable examples or package examples.
- `references/FORMATTING.md` - Read when formatting Godoc lists, paragraphs, links, and code blocks.

---

## Doc Comments

> **Normative**: All top-level exported names must have doc comments.

### Basic Rules

1. Begin with the name of the object being described
2. An article ("a", "an", "the") may precede the name
3. Use full sentences (capitalized, punctuated)

```go
// A Request represents a request to run a command.
type Request struct { ...

// Encode writes the JSON encoding of req to w.
func Encode(w io.Writer, req *Request) { ...
```

Unexported types/functions with unobvious behavior should also have doc comments.

> **Validation**: After adding doc comments, run `bash scripts/check-docs.sh` to verify no exported symbols are missing documentation. Fix any gaps before proceeding.

---

## Comment Sentences

> **Normative**: Documentation comments must be complete sentences.

- Capitalize the first word, end with punctuation
- Exception: may begin with uncapitalized identifier if clear
- End-of-line comments for struct fields can be phrases

---

## Comment Line Length

> **Advisory**: Aim for ~80 columns, but no hard limit.

Break based on punctuation. Don't split long URLs.

---

## Struct Documentation

Group fields with section comments. Mark optional fields with defaults:

```go
type Options struct {
    // General setup:
    Name  string
    Group *FooGroup

    // Customization:
    LargeGroupThreshold int // optional; default: 10
}
```

---

## Package Comments

> **Normative**: Every package must have exactly one package comment.

```go
// Package math provides basic constants and mathematical functions.
package math
```

- For `main` packages, use the binary name: `// The seed_generator command ...`
- For long package comments, use a `doc.go` file

---

## What to Document

> **Advisory**: Document non-obvious behavior, not obvious behavior.

| Topic | Document when... | Skip when... |
|-------|-----------------|--------------|
| Parameters | Non-obvious behavior, edge cases | Restates the type signature |
| Contexts | Behavior differs from standard cancellation | Standard `ctx.Err()` return |
| Concurrency | Ambiguous thread safety (e.g., read that mutates) | Read-only is safe, mutation is unsafe |
| Cleanup | Always document resource release | — |
| Errors | Sentinel values, error types (use `*PathError`) | — |
| Named results | Multiple params of same type, action-oriented names | Type alone is clear enough |

Key principles:

- Context cancellation returning `ctx.Err()` is implied — don't restate it
- Read-only ops are assumed thread-safe; mutations assumed unsafe — don't restate
- Always document cleanup requirements (e.g., `Call Stop to release resources`)
- Use pointer in error type docs (`*PathError`) for correct `errors.Is`/`errors.As`
- Don't name results just to enable naked returns — clarity > brevity

---

## Runnable Examples

> **Advisory**: Provide runnable examples in test files (`*_test.go`).

```go
func ExampleConfig_WriteTo() {
    cfg := &Config{Name: "example"}
    cfg.WriteTo(os.Stdout)
    // Output:
    // {"name": "example"}
}
```

Examples appear in Godoc attached to the documented element.

---

## Quick Reference

| Topic | Key Rule |
|-------|----------|
| Doc comments | Start with name, use full sentences |
| Line length | ~80 chars, prioritize readability |
| Package comments | One per package, above `package` clause |
| Parameters | Document non-obvious behavior only |
| Contexts | Document exceptions to implied behavior |
| Concurrency | Document ambiguous thread safety |
| Cleanup | Always document resource release |
| Errors | Document sentinels and types (note pointer) |
| Examples | Use runnable examples in test files |
| Formatting | Blank lines for paragraphs, indent for code |

---

## Related Skills

- **Naming conventions**: See [go-naming](../go-naming/SKILL.md) when choosing names for the identifiers your doc comments describe
- **Testing examples**: See [go-testing](../go-testing/SKILL.md) when writing runnable `Example` test functions that appear in godoc
- **Linting enforcement**: See [go-linting](../go-linting/SKILL.md) when using revive or other linters to enforce doc comment presence
- **Style principles**: See [go-style-core](../go-style-core/SKILL.md) when balancing documentation verbosity against clarity and concision