Go Documentation

This skill covers documentation conventions from Google's Go Style Guide.

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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)

// Good:
// 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) { ...

Struct Documentation

// Good:
// Options configure the group management service.
type Options struct {
    // General setup:
    Name  string
    Group *FooGroup

    // Dependencies:
    DB *sql.DB

    // Customization:
    LargeGroupThreshold int // optional; default: 10
    MinimumMembers      int // optional; default: 2
}

Unexported types/functions with unobvious behavior should also have doc comments. Use the same style to make future exporting easy.

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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:

// Good:
// A Server handles serving quotes from Shakespeare.
type Server struct {
    // BaseDir points to the base directory for Shakespeare's works.
    //
    // Expected structure:
    //   {BaseDir}/manifest.json
    //   {BaseDir}/{name}/{name}-part{number}.txt
    BaseDir string

    WelcomeMessage  string // displayed when user logs in
    ProtocolVersion string // checked against incoming requests
    PageLength      int    // lines per page (optional; default: 20)
}

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Comment Line Length

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

# Good:
// This is a comment paragraph.
// The length of individual lines doesn't matter in Godoc;
// but the choice of wrapping makes it easy to read on narrow screens.
//
// Don't worry too much about the long URL:
// https://supercalifragilisticexpialidocious.example.com:8080/Animalia/Chordata/

# Bad:
// This is a comment paragraph. The length of individual lines doesn't matter in
Godoc;
// but the choice of wrapping causes jagged lines on narrow screens or in code
review.

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

---

Package Comments

Normative: Every package must have exactly one package comment.

// Good:
// Package math provides basic constants and mathematical functions.
//
// This package does not guarantee bit-identical results across architectures.
package math

Main Packages

Use the binary name (matching the BUILD file):

// Good:
// The seed_generator command is a utility that generates a Finch seed file
// from a set of JSON study configs.
package main

Valid styles: Binary seed_generator, Command seed_generator, The seed_generator command, Seed_generator ...

Tips:

• For long package comments, use a doc.go file
• Maintainer comments after imports don't appear in Godoc

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Parameters and Configuration

Advisory: Document error-prone or non-obvious parameters, not everything.

// Bad: Restates the obvious
// Sprintf formats according to a format specifier and returns the resulting string.
//
// format is the format, and data is the interpolation data.
func Sprintf(format string, data ...any) string

// Good: Documents non-obvious behavior
// Sprintf formats according to a format specifier and returns the resulting string.
//
// The provided data is used to interpolate the format string. If the data does
// not match the expected format verbs or the amount of data does not satisfy
// the format specification, the function will inline warnings about formatting
// errors into the output string.
func Sprintf(format string, data ...any) string

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Contexts

Advisory: Don't restate implied context behavior; document exceptions.

Context cancellation is implied to interrupt the function and return ctx.Err(). Don't document this.

// Bad: Restates implied behavior
// Run executes the worker's run loop.
//
// The method will process work until the context is cancelled.
func (Worker) Run(ctx context.Context) error

// Good: Just the essential
// Run executes the worker's run loop.
func (Worker) Run(ctx context.Context) error

Document when behavior differs:

// Good: Non-standard cancellation behavior
// Run executes the worker's run loop.
//
// If the context is cancelled, Run returns a nil error.
func (Worker) Run(ctx context.Context) error

// Good: Special context requirements
// NewReceiver starts receiving messages sent to the specified queue.
// The context should not have a deadline.
func NewReceiver(ctx context.Context) *Receiver

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Concurrency

Advisory: Document non-obvious thread safety characteristics.

Read-only operations are assumed safe; mutating operations are assumed unsafe. Don't restate this.

Document when:

// Ambiguous operation (looks read-only but mutates internally)
// Lookup returns the data associated with the key from the cache.
//
// This operation is not safe for concurrent use.
func (*Cache) Lookup(key string) (data []byte, ok bool)

// API provides synchronization
// NewFortuneTellerClient returns an *rpc.Client for the FortuneTeller service.
// It is safe for simultaneous use by multiple goroutines.
func NewFortuneTellerClient(cc *rpc.ClientConn) *FortuneTellerClient

// Interface has concurrency requirements
// A Watcher reports the health of some entity (usually a backend service).
//
// Watcher methods are safe for simultaneous use by multiple goroutines.
type Watcher interface {
    Watch(changed chan<- bool) (unwatch func())
    Health() error
}

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Cleanup

Advisory: Always document explicit cleanup requirements.

// Good:
// NewTicker returns a new Ticker containing a channel that will send the
// current time on the channel after each tick.
//
// Call Stop to release the Ticker's associated resources when done.
func NewTicker(d Duration) *Ticker

// Good: Show how to clean up
// Get issues a GET to the specified URL.
//
// When err is nil, resp always contains a non-nil resp.Body.
// Caller should close resp.Body when done reading from it.
//
//    resp, err := http.Get("http://example.com/")
//    if err != nil {
//        // handle error
//    }
//    defer resp.Body.Close()
//    body, err := io.ReadAll(resp.Body)
func (c *Client) Get(url string) (resp *Response, err error)

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Errors

Advisory: Document significant error sentinel values and types.

// Good: Document sentinel values
// Read reads up to len(b) bytes from the File and stores them in b.
//
// At end of file, Read returns 0, io.EOF.
func (*File) Read(b []byte) (n int, err error)

// Good: Document error types (include pointer receiver)
// Chdir changes the current working directory to the named directory.
//
// If there is an error, it will be of type *PathError.
func Chdir(dir string) error

Noting *PathError (not PathError) enables correct use of errors.Is and errors.As.

For package-wide error conventions, document in the package comment.

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Examples

Advisory: Provide runnable examples to demonstrate package usage.

Place examples in test files (*_test.go):

// Good:
func ExampleConfig_WriteTo() {
    cfg := &Config{
        Name: "example",
    }
    if err := cfg.WriteTo(os.Stdout); err != nil {
        log.Exitf("Failed to write config: %s", err)
    }
    // Output:
    // {
    //   "name": "example"
    // }
}

Examples appear in Godoc attached to the documented element.

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Godoc Formatting

Advisory: Use godoc syntax for well-formatted documentation.

Paragraphs - Separate with blank lines:

// Good:
// LoadConfig reads a configuration out of the named file.
//
// See some/shortlink for config file format details.

Verbatim/Code blocks - Indent by two additional spaces:

// Good:
// Update runs the function in an atomic transaction.
//
// This is typically used with an anonymous TransactionFunc:
//
//   if err := db.Update(func(state *State) { state.Foo = bar }); err != nil {
//     //...
//   }

Lists and tables - Use verbatim formatting:

// Good:
// LoadConfig treats the following keys in special ways:
//   "import" will make this configuration inherit from the named file.
//   "env" if present will be populated with the system environment.

Headings - Single line, capital letter, no punctuation (except parens/commas), followed by paragraph:

// Good:
// Using headings
//
// Headings come with autogenerated anchor tags for easy linking.

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Named Result Parameters

Advisory: Use for documentation when types alone aren't clear enough.

// Good: Multiple params of same type
func (n *Node) Children() (left, right *Node, err error)

// Good: Action-oriented name clarifies usage
// The caller must arrange for the returned cancel function to be called.
func WithTimeout(parent Context, d time.Duration) (ctx Context, cancel func())

// Bad: Type already clear, name adds nothing
func (n *Node) Parent1() (node *Node)
func (n *Node) Parent2() (node *Node, err error)

// Good: Type is sufficient
func (n *Node) Parent1() *Node
func (n *Node) Parent2() (*Node, error)

Don't name results just to enable naked returns. Clarity > brevity.

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Signal Boosting

Advisory: Add comments to highlight unusual or easily-missed patterns.

These two are hard to distinguish:

if err := doSomething(); err != nil {  // common
    // ...
}

if err := doSomething(); err == nil {  // unusual!
    // ...
}

Add a comment to boost the signal:

// Good:
if err := doSomething(); err == nil { // if NO error
    // ...
}

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Documentation Preview

Advisory: Preview documentation before and during code review.

go install golang.org/x/pkgsite/cmd/pkgsite@latest
pkgsite

This validates godoc formatting renders correctly.

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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

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See Also

• go-style-core - Core Go style principles and formatting guidelines
• go-naming - Naming conventions for Go identifiers
• go-linting - Linting tools for documentation and code quality