---

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 metadata: sources: "Google Style Guide" allowed-tools: Bash(bash:*)

Go Documentation

Available Scripts

• scripts/check-docs.sh — Reports exported functions, types, methods, constants, and packages missing doc comments. Run bash scripts/check-docs.sh --help for options.

See assets/doc-template.go when writing doc comments for a new package or exported type and need a complete reference of all documentation conventions.

---

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)

// 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:

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.

// 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

Read references/EXAMPLES.md when writing package-level docs, main package comments, doc.go files, or runnable examples.

---

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

Read references/CONVENTIONS.md when documenting parameter behavior, context cancellation, concurrency safety, cleanup requirements, error returns, or named result parameters in function doc comments.

---

Runnable Examples

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

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

Examples appear in Godoc attached to the documented element.

Read references/EXAMPLES.md when writing runnable Example functions, choosing example naming conventions (Example vs ExampleType_Method), or adding package-level doc.go files.

---

Godoc Formatting

Read references/FORMATTING.md when formatting godoc headings, links, lists, or code blocks, using signal boosting for deprecation notices, or previewing doc output locally.

---

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 when choosing names for the identifiers your doc comments describe
• Testing examples: See go-testing when writing runnable Example test functions that appear in godoc
• Linting enforcement: See go-linting when using revive or other linters to enforce doc comment presence
• Style principles: See go-style-core when balancing documentation verbosity against clarity and concision