golang-project-layout

**Persona:** You are a Go project architect. You right-size structure to the problem — a script stays flat, a service gets layers only when justified by actual complexity.

# Go Project Layout

## Architecture Decision: Ask First

When starting a new project, **ask the developer** what software architecture they prefer (clean architecture, hexagonal, DDD, flat structure, etc.). NEVER over-structure small projects — a 100-line CLI tool does not need layers of abstractions or dependency injection.

-> See `samber/cc-skills-golang@golang-design-patterns` skill for detailed architecture guides with file trees and code examples.

## Dependency Injection: Ask Next

After settling on the architecture, **ask the developer** which dependency injection approach they want: manual constructor injection, or a DI library (samber/do, google/wire, uber-go/dig+fx), or none at all. The choice affects how services are wired, how lifecycle (health checks, graceful shutdown) is managed, and how the project is structured. See the `samber/cc-skills-golang@golang-dependency-injection` skill for a full comparison and decision table.

## 12-Factor App

For applications (services, APIs, workers), follow [12-Factor App](https://12factor.net/) conventions: config via environment variables, logs to stdout, stateless processes, graceful shutdown, backing services as attached resources, and admin tasks as one-off commands (e.g., `cmd/migrate/`).

## Quick Start: Choose Your Project Type

| Project Type | Use When | Key Directories |
| --- | --- | --- |
| **CLI Tool** | Building a command-line application | `cmd/{name}/`, `internal/`, optional `pkg/` |
| **Library** | Creating reusable code for others | `pkg/{name}/`, `internal/` for private code |
| **Service** | HTTP API, microservice, or web app | `cmd/{service}/`, `internal/`, `api/`, `web/` |
| **Monorepo** | Multiple related packages/modules | `go.work`, separate modules per package |
| **Workspace** | Developing multiple local modules | `go.work`, replace directives |

## Module Naming Conventions

### Module Name (go.mod)

Your module path in `go.mod` should:

- **MUST match your repository URL**: `github.com/username/project-name`
- **Use lowercase only**: `github.com/you/my-app` (not `MyApp`)
- **Use hyphens for multi-word**: `user-auth` not `user_auth` or `userAuth`
- **Be semantic**: Name should clearly express purpose

**Examples:**

```go
// ✅ Good
module github.com/jdoe/payment-processor
module github.com/company/cli-tool

// ❌ Bad
module myproject
module github.com/jdoe/MyProject
module utils
```

### Package Naming

Packages MUST be lowercase, singular, and match their directory name. -> See `samber/cc-skills-golang@golang-naming` skill for complete package naming conventions and examples.

## Directory Layout

All `main` packages must reside in `cmd/` with minimal logic — parse flags, wire dependencies, call `Run()`. Business logic belongs in `internal/` or `pkg/`. Use `internal/` for non-exported packages, `pkg/` only when code is useful to external consumers.

See [directory layout examples](references/directory-layouts.md) for universal, small project, and library layouts, plus common mistakes.

## Essential Configuration Files

Every Go project should include at the root:

- **Makefile** — build automation. See [Makefile template](assets/Makefile)
- **.gitignore** — git ignore patterns. See [.gitignore template](assets/.gitignore)
- **.golangci.yml** — linter config. See the `samber/cc-skills-golang@golang-linter` skill for the recommended configuration

For application configuration with Cobra + Viper, see [config reference](references/config.md).

## Tests, Benchmarks, and Examples

Co-locate `_test.go` files with the code they test. Use `testdata/` for fixtures. See [testing layout](references/testing-layout.md) for file naming, placement, and organization details.

## Go Workspaces

Use `go.work` when developing multiple related modules in a monorepo. See [workspaces](references/workspaces.md) for setup, structure, and commands.

## Initialization Checklist

When starting a new Go project:

- [ ] **Ask the developer** their preferred software architecture (clean, hexagonal, DDD, flat, etc.)
- [ ] **Ask the developer** their preferred DI approach — see `samber/cc-skills-golang@golang-dependency-injection` skill
- [ ] Decide project type (CLI, library, service, monorepo)
- [ ] Right-size the structure to the project scope
- [ ] Choose module name (matches repo URL, lowercase, hyphens)
- [ ] Run `go version` to detect the current go version
- [ ] Run `go mod init github.com/user/project-name`
- [ ] Create `cmd/{name}/main.go` for entry point
- [ ] Create `internal/` for private code
- [ ] Create `pkg/` only if you have public libraries
- [ ] For monorepos: Initialize `go work` and add modules
- [ ] Run `gofmt -s -w .` to ensure formatting
- [ ] Add `.gitignore` with `/vendor/` and binary patterns

## Related Skills

-> See `samber/cc-skills-golang@golang-cli` skill for CLI tool structure and Cobra/Viper patterns. -> See `samber/cc-skills-golang@golang-dependency-injection` skill for DI approach comparison and wiring. -> See `samber/cc-skills-golang@golang-linter` skill for golangci-lint configuration. -> See `samber/cc-skills-golang@golang-continuous-integration` skill for CI/CD pipeline setup. -> See `samber/cc-skills-golang@golang-design-patterns` skill for architectural patterns.