Go Documentation

Go Documentation

Godoc is not free-form prose — it's a convention the toolchain renders. Comments that follow the convention become browsable documentation on pkg.go.dev; comments that don't become noise.

1. Doc Comment Form

Every exported identifier gets a doc comment. It starts with the identifier's name and is a complete sentence:

// ✅ Good
// ParseDuration parses a duration string such as "300ms" or "2h45m".
// It returns an error if the string is not a valid duration.
func ParseDuration(s string) (Duration, error) { ... }

// ❌ Bad — doesn't start with the name, fragment, restates signature
// this function parses durations
func ParseDuration(s string) (Duration, error) { ... }

• Groups of related constants/variables may share one comment on the block: // Common HTTP methods. above the const (...) group.
• Unexported identifiers: comment when the purpose isn't obvious from the name — same form, no obligation.
• Say what the caller needs: behavior, error conditions, nil/zero-value handling, concurrency safety. Not the implementation.

2. Package Documentation

One package comment per package, on the package clause. For more than a few sentences, put it in a dedicated doc.go:

// Package retry implements backoff strategies for retrying failed
// operations.
//
// The zero value of Policy retries three times with exponential
// backoff. Use functional options to customize:
//
//	p := retry.NewPolicy(retry.WithMaxAttempts(5))
//	err := p.Do(ctx, fetchUser)
package retry

• Begins with "Package ...".
• Indented lines (one tab) render as code blocks.
• main packages: the comment describes the command and its flags — it becomes the command's documentation.

3. Doc Links and Formatting (Go 1.19+)

// Fetch retrieves the resource. It honors the deadline of ctx and
// returns [ErrNotFound] if the resource does not exist.
//
// For batch retrieval use [Client.FetchAll]. See the [net/http]
// package for transport configuration.
func (c *Client) Fetch(ctx context.Context, id string) (*Resource, error)

• [Name], [Type.Method], [pkg/path] become hyperlinks on pkg.go.dev.
• A line starting with # is a heading (rare; only in long package docs).
• Lists: lines starting with a space and a bullet. Keep them shallow.

4. Testable Examples

Example functions are documentation the compiler checks. Put them in example_test.go in the <pkg>_test package:

func ExampleParseDuration() {
    d, _ := ParseDuration("1h30m")
    fmt.Println(d.Minutes())
    // Output: 90
}

// Method example: ExampleType_Method
func ExamplePolicy_Do() { ... }

// Second example for the same symbol: suffix
func ExampleParseDuration_negative() { ... }

• The // Output: comment makes it a test — go test fails if the printed output differs. Examples without it compile but don't run.
• Write an example for every non-trivial exported API. It renders directly under the symbol on pkg.go.dev.

5. Deprecation

// Fetch retrieves the resource.
//
// Deprecated: Use [Client.FetchContext] instead, which honors
// context cancellation.
func (c *Client) Fetch(id string) (*Resource, error)

• The paragraph must start exactly with Deprecated: .
• Always name the replacement.
• Tools (gopls, staticcheck, pkg.go.dev) surface these automatically.

6. What NOT to Write

// ❌ Noise — restates the code
// GetName returns the name.
func (u *User) GetName() string { return u.name }

// ❌ Maintenance history — belongs in git
// Changed 2024-03-01 by alice: added caching.

// ❌ Commented-out code kept "for reference"

If a doc comment can only restate the signature, improve the name until the comment says something the signature can't — or accept a minimal comment for symmetry in a fully documented API.

Executable Verification

go vet ./...                  # flags some malformed doc comments
gofmt -l .                    # Go 1.19+ gofmt normalizes doc comments
go test ./...                 # runs Example functions with Output
go doc ./mypkg Symbol         # render what users will actually see

For a browsable preview, run a local pkgsite if available: go run golang.org/x/pkgsite/cmd/pkgsite@latest and open the module.

Verification Checklist

1. Every exported identifier has a doc comment starting with its name
2. Package has a package comment ("Package ..."), in doc.go if long
3. Error conditions and nil/zero-value behavior documented for exported APIs
4. Concurrency safety stated where callers could guess wrong
5. [Symbol] doc links used instead of bare names in running text
6. Non-trivial exported APIs have Example functions with // Output:
7. Deprecations use the exact Deprecated: form and name a replacement
8. No comments restating signatures, tracking history, or holding dead code
9. go test ./... passes with examples enabled