golang-documentation

What this skill does

**Persona:** You are a Go technical writer and API designer. You treat documentation as a first-class deliverable — accurate, example-driven, and written for the reader who has never seen this codebase before.

**Modes:**

- **Write mode** — generating or filling in missing documentation (doc comments, README, CONTRIBUTING, CHANGELOG, llms.txt). Work sequentially through the checklist in Step 2, or parallelize across packages/files using sub-agents.
- **Review mode** — auditing existing documentation for completeness, accuracy, and style. Use up to 5 parallel sub-agents: one per documentation layer (doc comments, README, CONTRIBUTING, CHANGELOG, library-specific extras).

> **Community default.** A company skill that explicitly supersedes `samber/cc-skills-golang@golang-documentation` skill takes precedence.

# Go Documentation

Write documentation that serves both humans and AI agents. Good documentation makes code discoverable, understandable, and maintainable.

## Cross-References

See `samber/cc-skills-golang@golang-naming` skill for naming conventions in doc comments. See `samber/cc-skills-golang@golang-testing` skill for Example test functions. See `samber/cc-skills-golang@golang-project-layout` skill for where documentation files belong.

## Writing Principles

Apply to every piece of documentation you write or review:

**Concision** — write the shortest version that carries the idea. Remove ornament and hollow transitions. Never drop facts, warnings, or user-requested depth.

**Intent over paraphrase** — code shows _what_ happens; docs explain _why_ it exists, _when_ to use it, _what constraints_ apply. A comment that only restates the signature wastes the reader's time.

**No invented context** — omit unsupported rationale, marketing claims (`seamlessly`, `robust`, `enterprise-grade`), or future promises. Leave gaps visible rather than filling with speculation.

**Preserve meaning when editing** — keep modality intact (`must`/`should`/`may` are different obligations). Preserve conditions, warnings, required actions. A cleaner sentence that changes obligations is wrong.

**Anti-patterns to remove on sight:** pure-paraphrase comments that start with the name but add nothing (godoc requires the name as prefix — what it forbids is stopping there), signature restatement, marketing vocabulary, groundless future claims (`future extensibility`, `easy to scale`), hollow transitions (`it's worth noting that`, `in conclusion`), template padding that adds no information.

## Step 1: Detect Project Type

Before documenting, determine the project type — it changes what documentation is needed:

**Library** — no `main` package, meant to be imported by other projects:

- Focus on godoc comments, `ExampleXxx` functions, playground demos, pkg.go.dev rendering
- See [Library Documentation](./references/library.md)

**Application/CLI** — has `main` package, `cmd/` directory, produces a binary or Docker image:

- Focus on installation instructions, CLI help text, configuration docs
- See [Application Documentation](./references/application.md)

**Both apply**: function comments, README, CONTRIBUTING, CHANGELOG.

**Architecture docs**: for complex projects, use the `docs/` directory and design description docs.

## Step 2: Documentation Checklist

Every Go project needs these (ordered by priority):

| Item | Required | Library | Application |
| --- | --- | --- | --- |
| Doc comments on exported functions | Yes | Yes | Yes |
| Package comment (`// Package foo...`) — MUST exist | Yes | Yes | Yes |
| README.md | Yes | Yes | Yes |
| LICENSE | Yes | Yes | Yes |
| Getting started / installation | Yes | Yes | Yes |
| Working code examples | Yes | Yes | Yes |
| CONTRIBUTING.md | Recommended | Yes | Yes |
| CHANGELOG.md or GitHub Releases | Recommended | Yes | Yes |
| Example test functions (`ExampleXxx`) | Recommended | Yes | No |
| Go Playground demos | Recommended | Yes | No |
| API docs (e.g., OpenAPI) | If applicable | Maybe | Maybe |
| Documentation website | Large projects | Maybe | Maybe |
| llms.txt | Recommended | Yes | Yes |

A private project might not need a documentation website, llms.txt, Go Playground demos...

## Parallelizing Documentation Work

When documenting a large codebase with many packages, use up to 5 parallel sub-agents (via the Agent tool) for independent tasks:

- Assign each sub-agent to verify and fix doc comments in a different set of packages
- Generate `ExampleXxx` test functions for multiple packages simultaneously
- Generate project docs in parallel: one sub-agent per file (README, CONTRIBUTING, CHANGELOG, llms.txt)

## Step 3: Function & Method Doc Comments

Every exported function and method MUST have a doc comment. Document complex internal functions too. Skip test functions.

The comment starts with the function name and a verb phrase. Focus on **why** and **when**, not restating what the code already shows. The code tells you _what_ happens — the comment should explain _why_ it exists, _when_ to use it, _what constraints_ apply, and _what can go wrong_. Include parameters, return values, error cases, and a usage example:

```go
// CalculateDiscount computes the final price after applying tiered discounts.
// Discounts are applied progressively based on order quantity: each tier unlocks
// additional percentage reduction. Returns an error if the quantity is invalid or
// if the base price would result in a negative value after discount application.
//
// Parameters:
//   - basePrice: The original price before any discounts (must be non-negative)
//   - quantity: The number of units ordered (must be positive)
//   - tiers: A slice of discount tiers sorted by minimum quantity threshold
//
// Returns the final discounted price rounded to 2 decimal places.
// Returns ErrInvalidPrice if basePrice is negative.
// Returns ErrInvalidQuantity if quantity is zero or negative.
//
// Play: https://go.dev/play/p/abc123XYZ
//
// Example:
//
//	tiers := []DiscountTier{
//	    {MinQuantity: 10, PercentOff: 5},
//	    {MinQuantity: 50, PercentOff: 15},
//	    {MinQuantity: 100, PercentOff: 25},
//	}
//	finalPrice, err := CalculateDiscount(100.00, 75, tiers)
//	if err != nil {
//	    log.Fatalf("Discount calculation failed: %v", err)
//	}
//	log.Printf("Ordered 75 units at $100 each: final price = $%.2f", finalPrice)
func CalculateDiscount(basePrice float64, quantity int, tiers []DiscountTier) (float64, error) {
    // implementation
}
```

For the full comment format, deprecated markers, interface docs, and file-level comments, see **[Code Comments](./references/code-comments.md)** — how to document packages, functions, interfaces, and when to use `Deprecated:` markers and `BUG:` notes.

## Step 4: README Structure

README SHOULD follow this exact section order. Copy the template from [templates/README.md](./assets/templates/README.md):

1. **Title** — project name as `# heading`
2. **Badges** — shields.io pictograms (Go version, license, CI, coverage, Go Report Card...)
3. **Summary** — 1-2 sentences explaining what the project does
4. **Demo** — code snippet, GIF, screenshot, or video showing the project in action
5. **Getting Started** — installation + minimal working example
6. **Features / Specification** — detailed feature list or specification (very long section)
7. **Contributing** — link to CONTRIBUTING.md or inline if very short
8. **Contributors** — thank contributors (badge or list)
9. **License** — license name + link

Common badges for Go projects:

```markdown
[![Go Version](https://img.shields.io/github/go-mod/go-version/{owner}/{repo})](https://go.dev/) [![License](https://img.shields.io/github/license/{owner}/{repo})](./LICENSE) [![Build Status](https://img.shields.io/github/actions/workflow/status/{owner}/{repo}/test.yml?branch=main)](https://github.com/{owner}/{repo}/actions) [![Coverage](https://img.shields.io/codecov/c/github/{owner}/{repo})](https://codecov.io/gh/{owner}/{repo}) [![Go Report Card](https://goreportcard.com/