Go CLI Builder

Go CLI Builder

Overview

This skill provides templates, scripts, and patterns for building production-ready Go command-line tools. It follows established patterns from projects like feedspool-go, feed-to-mastodon, and linkding-to-opml.

The skill generates projects with:

• Cobra for CLI framework
• Viper for configuration management (YAML files with CLI overrides)
• SQLite with a naive migration system
• Logrus for structured logging
• Makefile for common tasks (lint, format, test, build)
• GitHub Actions workflows for CI, tagged releases, and rolling releases
• Strict code formatting with gofumpt and linting with golangci-lint

When to Use This Skill

Use this skill when:

• Creating a new Go CLI tool from scratch
• Adding commands to an existing Go CLI project that follows these patterns
• Needing reference material about Cobra/Viper integration
• Setting up GitHub Actions workflows for multi-platform Go releases

Example user requests:

• "Create a new Go CLI tool called feed-analyzer"
• "Scaffold a Go project for processing log files"
• "Add a new 'export' command to my Go CLI project"
• "Help me set up GitHub Actions for releasing my Go tool"

Quick Start

Creating a New Project

To scaffold a complete new project:

# With database support (default)
python scripts/scaffold_project.py my-cli-tool

# Without database support
python scripts/scaffold_project.py my-cli-tool --no-database

# With template support for generating output
python scripts/scaffold_project.py my-cli-tool --templates

# Combining options
python scripts/scaffold_project.py my-cli-tool --no-database --templates

Project Options:

• Database Support (default: included)

  • Includes SQLite with migrations system
  • Use --no-database to exclude if you don't need persistent storage
  • Examples: CLI tools that only fetch/transform data, API clients

• Template Support (default: excluded)

  • Includes embedded template system with init command
  • Use --templates to include for tools that generate formatted output
  • Examples: Markdown generators, OPML exporters, report generators

What gets created:

Base structure (always):

• Entry point (main.go)
• Root command with Cobra/Viper integration (cmd/root.go)
• Version command (cmd/version.go)
• Configuration system (internal/config/)
• Makefile with standard targets
• GitHub Actions workflows (CI, release, rolling-release)

Optional additions:

• Database layer with migrations (internal/database/) - if database enabled
• Template system (internal/templates/, cmd/init.go) - if templates enabled

Next steps after scaffolding:

1. Update go.mod with the actual module name
2. Customize the example config file
3. If using database: Define initial schema in internal/database/schema.sql
4. Run make setup to install development tools
5. Run go mod tidy to download dependencies

Adding Commands to Existing Projects

To add a new command to an existing project:

python scripts/add_command.py fetch

This creates cmd/fetch.go with:

• Command boilerplate
• Access to logger and config
• Flag binding examples
• TODO comments for implementation

Project Structure

Generated projects follow this structure:

my-cli-tool/
├── main.go                          # Entry point
├── go.mod                           # Dependencies
├── Makefile                         # Build automation
├── my-cli-tool.yaml.example         # Example configuration
├── cmd/                             # Command definitions
│   ├── root.go                      # Root command + Cobra/Viper setup
│   ├── version.go                   # Version command
│   ├── constants.go                 # Application constants
│   └── [command].go                 # Individual commands
├── internal/
│   ├── config/
│   │   └── config.go                # Configuration struct
│   ├── database/
│   │   ├── database.go              # Connection + initialization
│   │   ├── migrations.go            # Migration system
│   │   └── schema.sql               # Initial schema (embedded)
│   └── templates/                   # Optional: For tools that generate output
│       ├── templates.go             # Embedded template loader
│       └── default.md               # Default template (embedded)
└── .github/workflows/
    ├── ci.yml                       # PR linting and testing
    ├── release.yml                  # Tagged releases
    └── rolling-release.yml          # Main branch rolling releases

Configuration System

Projects use a three-tier configuration hierarchy:

1. Config file (my-tool.yaml): Base configuration in YAML
2. Environment variables: Automatic via Viper
3. CLI flags: Override everything

See references/cobra-viper-integration.md for detailed patterns on:

• Binding flags to Viper keys
• Adding new configuration options
• Command-specific vs. global configuration
• Environment variable mapping

Database Layer

The generated database layer includes:

1. Initial schema (internal/database/schema.sql): Embedded SQL for first-time setup
2. Migration tracking: schema_migrations table tracks applied versions
3. Migration execution: Automatic on database initialization
4. Idempotent operations: Safe to run multiple times

To add a new migration:

1. Edit internal/database/migrations.go
2. Add to the getMigrations() map with the next version number:

   func getMigrations() map[int]string {
       return map[int]string{
           2: `CREATE TABLE IF NOT EXISTS settings (
               key TEXT PRIMARY KEY,
               value TEXT NOT NULL
           );`,
       }
   }
   

3. Migrations run automatically on next database initialization

Init Command Pattern

For tools that generate output files (markdown, OPML, etc.), the init command pattern provides a great user experience by generating both configuration and customizable templates.

When to Use Init Command

Use the init command when your CLI tool:

• Generates formatted output (markdown, HTML, XML, etc.)
• Benefits from user-customizable templates
• Has configuration that users need to set up before first use

Init Command Components

Available templates:

• init.go.template - Complete init command implementation
• templates.go.template - Template loader with embedded default
• default.md.template - Example embedded markdown template

The init command:

1. Creates a YAML configuration file with all options documented
2. Creates a customizable template file (using embedded default)
3. Supports --force flag to overwrite existing files
4. Supports --template-file flag to specify custom template filename
5. Provides helpful next steps after initialization

Embedded Templates

Go's //go:embed directive allows embedding template files directly in the binary:

package templates

import (
    _ "embed"
)

//go:embed default.md
var defaultTemplate string

func GetDefaultTemplate() (string, error) {
    return defaultTemplate, nil
}

Benefits:

• Single binary distribution (no external template files needed)
• Users can still customize by running init to get a copy
• Template always available as fallback

Integration with Other Commands

Commands that generate output should support both:

1. Built-in template (default) - uses embedded template
2. Custom template (via --template flag or config) - loads from file

Example pattern:

templatePath := viper.GetString("command.template")
var generator *Generator
if templatePath != "" {
    generator, err = NewGeneratorFromFile(templatePath)
} else {
    generator, err = NewGenerator() // uses embedded default
}

Example Projects Using This Pattern

• linkding-to-markdown - Fetches bookmarks and generates markdown
• mastodon-to-markdown - Exports Mastodon posts to markdown

Orchestrator-friendly export Contract

Scope: this contract applies only to tools whose purpose is to fetch data from a source and transform it into a Markdown document. Other Go CLIs the skill might be used to build (servers, web apps, generic utilities) are not in scope.

Tools that conform to the contract can be orchestrated by me-to-markdown, which runs many such tools in parallel over a single time window and concatenates their output into one combined Markdown document.

The contract

Every fetch-and-export tool exposes an export subcommand the orchestrator calls:

{tool} export --since <date|duration> [--until <date>] [-o <file>]

• --since — required. Accepts a Go duration string (168h, 30m), an RFC3339 timestamp, or a YYYY-MM-DD date. Durations are interpreted as "ago" relative to now.
• --until — optional. Accepts YYYY-MM-DD (end-of-day inclusive in local time) or RFC3339. Defaults to "now" when omitted.
• -o / --output — output file path. Empty (or -) means stdout.

That's the full surface. Filter, sort, formatting, and other tool-specific options stay in the config file rather than the export flag set — the orchestrator-facing contract is deliberately minimal.

Posture: purely additive

export is added alongside any existing fetch, sync, render, run, or root command — never as a replacement. Existing user-visible behavior on those commands stays unchanged. This keeps the normalization PR low-risk and lets downstream consumers (other tools, scripts, agent skills) keep calling whatever they already call.

Composition pattern

• Stateless tools (fetch directly from an API, render in one pass): extract the post-flag-parsing pipeline into a function, then both the legacy fetch and the new export call it. Example: mastodon-to-markdown's cmd/fetch.go exposes a runFetchPipeline that takes a *TimeRange and an output path; both subcommands build their own time range and delegate.
• Archive tools (local SQLite, sync separate from render): export composes sync + windowed render. Set viper keys for any values that render reads, then call syncCmd.RunE then renderCmd.RunE. Example: pocketcasts-to-markdown's cmd/export.go overrides render.since / render.until / render.output and delegates.

Time window parser

Drop in this exact file at internal/timewindow/parse.go. It's duplicated per-tool by design — the contract is small, stable, and not worth a cross-repo Go module dependency.

// Package timewindow parses the canonical --since/--until flag values
// used by the orchestrator-facing export subcommand.
package timewindow

import (
	"fmt"
	"time"
)

// Parse interprets s as one of:
//   - a Go duration string ("168h", "30m") — returned as ref.Add(-d)
//     (durations are interpreted as "ago" relative to ref);
//   - an RFC3339 timestamp;
//   - a YYYY-MM-DD date in the local timezone.
//
// When endOfDay is true, a YYYY-MM-DD date is advanced to end-of-day.
// RFC3339 and durations ignore endOfDay. Empty s returns an error.
func Parse(s string, ref time.Time, endOfDay bool) (time.Time, error) {
	if s == "" {
		return time.Time{}, fmt.Errorf("empty time value")
	}
	if d, err := time.ParseDuration(s); err == nil {
		return ref.Add(-d), nil
	}
	if t, err := time.Parse(time.RFC3339, s); err == nil {
		return t, nil
	}
	if t, err := time.ParseInLocation("2006-01-02", s, time.Local); err == nil {
		if endOfDay {
			t = t.Add(24*time.Hour - time.Nanosecond)
		}
		return t, nil
	}
	return time.Time{}, fmt.Errorf("invalid time %q (expected YYYY-MM-DD, RFC3339, or Go duration)", s)
}

Reference implementations

The following tools already implement the contract; lift the patterns directly:

• mastodon-to-markdown — stateless, extracts runFetchPipeline.
• linkding-to-markdown — stateless, similar shape.
• github-to-markdown — stateless, root command stays as the implicit fetch.
• pocketcasts-to-markdown — archive tool, simplest implementation (delegates to existing sync + render).
• spotify-to-markdown — archive tool, more invasive (adds PlaysBetween query, threads --since/--until through render).

State / database location

For archive tools, default the local SQLite path to $XDG_STATE_HOME/{tool-name}/state.db, falling back to ~/.local/state/{tool-name}/state.db. --database stays as an escape hatch. The orchestrator never overrides this — each tool owns its own state directory.

func xdgStateDir() string {
	if v := os.Getenv("XDG_STATE_HOME"); v != "" {
		return filepath.Join(v, "tool-name")
	}
	home, err := os.UserHomeDir()
	if err != nil {
		return "."
	}
	return filepath.Join(home, ".local", "state", "tool-name")
}

func defaultDatabasePath() string {
	return filepath.Join(xdgStateDir(), "state.db")
}

Set this as the viper default for the database key.

Makefile Targets

All generated projects include these targets:

• make setup: Install development tools (gofumpt, golangci-lint)
• make build: Build the binary with version information
• make run: Build and run the application
• make lint: Run golangci-lint
• make format: Format code with go fmt and gofumpt
• make test: Run tests with race detection
• make clean: Remove build artifacts

GitHub Actions Workflows

Three workflows are included:

1. CI (ci.yml)

• Triggers: Pull requests to main, manual workflow calls
• Actions: Lint with golangci-lint, test with race detection
• Skip: Commits starting with [noci]

2. Release (release.yml)

• Triggers: Tags matching v* (e.g., v1.0.0)
• Platforms: Linux (amd64, arm64), macOS (amd64, arm64), Windows (amd64)
• Outputs: Compressed binaries, checksums, GitHub release
• Docker: Optional (commented out by default)

3. Rolling Release (rolling-release.yml)

• Triggers: Pushes to main branch
• Actions: Same as Release but creates a "latest" prerelease
• Purpose: Testing builds from the latest commit

To customize:

• Update Docker Hub username in workflows if using Docker
• Adjust Go version if needed (default: 1.21)
• Modify build matrix to add/remove platforms

Typical Workflow

Starting a New Project

1. Use this skill to scaffold the project
2. Customize the initial schema in internal/database/schema.sql
3. Update configuration struct in internal/config/config.go
4. Add domain-specific packages in internal/ (see references/internal-organization.md)
5. Add commands using the add_command script
6. Implement command logic, calling into internal/ packages

Adding a Feature

1. Determine if it needs a new command or extends existing one
2. If new command: use add_command.py script
3. Add any required configuration to config struct and root flags
4. Implement logic in internal/ packages
5. Update command to call the internal logic
6. Add tests
7. Run make format && make lint && make test

Reference Documentation

For detailed patterns and guidelines, refer to:

• references/cobra-viper-integration.md: Complete guide to configuration system

  • Flag binding patterns
  • Adding new configuration options
  • Environment variable mapping
  • Best practices

• references/internal-organization.md: Internal package structure

  • Package organization principles
  • Dependency rules
  • Common patterns (Option pattern, error wrapping)
  • When to create new packages

• references/template-patterns.md: Template-based output generation

  • When and how to use embedded templates
  • Init command implementation
  • Generator/renderer patterns
  • Template functions and testing
  • User workflow and best practices

Templates Available

All templates are in assets/templates/:

Core Files:

• main.go: Minimal entry point
• go.mod.template: Pre-configured dependencies
• Makefile.template: Standard build targets
• gitignore.template: Go-specific ignores
• config.yaml.example: Example configuration

Commands:

• root.go.template: Cobra/Viper integration
• version.go.template: Version command
• constants.go.template: Application constants
• command.go.template: New command template
• init.go.template: Init command for config/template generation

Internal Packages:

• config.go.template: Configuration struct
• database.go.template: Database layer
• migrations.go.template: Migration system
• schema.sql.template: Initial schema
• templates.go.template: Embedded template loader
• default.md.template: Example embedded template

CI/CD:

• ci.yml.template: CI workflow
• release.yml.template: Release workflow
• rolling-release.yml.template: Rolling release workflow

Best Practices

1. Keep commands thin: Business logic belongs in internal/ packages
2. Use the config struct: Access configuration through GetConfig() rather than calling Viper directly
3. Wrap errors: Always add context with fmt.Errorf("context: %w", err)
4. Format before committing: Run make format && make lint
5. Test with race detection: go test -race ./...
6. Version your releases: Use semantic versioning tags (v1.0.0, v1.1.0, etc.)
7. Document in .yaml.example: Keep example config updated
8. Handle errors explicitly: Use _ = for intentionally ignored errors (e.g., _ = viper.BindPFlag(...))
9. Defer cleanup safely: Use defer func() { _ = tx.Rollback() }() instead of defer tx.Rollback() to avoid linter warnings

Common Customizations

After scaffolding, projects typically need:

1. Module name update: Change github.com/yourusername/project in go.mod to actual path
2. Additional dependencies: Add with go get and run go mod tidy
3. Custom schema: Define tables in internal/database/schema.sql
4. Domain packages: Create packages in internal/ for business logic
5. Command implementations: Fill in the TODOs in command files
6. Docker configuration: Uncomment Docker sections in workflows if needed

Recent Improvements

Linter Compliance (2025-11-11)

• Fixed viper.BindPFlag warnings: All viper.BindPFlag() calls now use _ = prefix to explicitly ignore errors, satisfying the errcheck linter
• Fixed defer Rollback warnings: Database transaction cleanup now uses defer func() { _ = tx.Rollback() }() pattern
• Removed static linking: Removed -linkmode external -extldflags "-static" flags from Makefile to eliminate getaddrinfo warnings when using CGO with SQLite
• Updated templates: All templates now generate linter-clean code out of the box

These changes ensure that projects scaffolded with this skill pass golangci-lint without warnings.

Troubleshooting

"gofumpt not found" or "golangci-lint not found"

• Run make setup to install development tools

"Failed to initialize schema"

• Check database file path and permissions
• Ensure directory exists or is creatable

"Missing migration for version N"

• Migrations must be sequential; add any missing versions

"getaddrinfo warning during build"

• This warning has been resolved in recent versions by removing static linking flags
• If you see this in an older project, remove the static linking lines from your Makefile (see Recent Improvements section)

GitHub Actions failing on cross-compilation

• Ensure CGO is enabled for SQLite
• Linux ARM64 builds require cross-compilation tools (handled in workflow)