Coding Agent Extension Builder

coding-agent-extension-builder

Kotlin library for generating coding agent extensions with compile-time safety.

Why Use This Library

Writing extensions by hand is error-prone:

• Need to remember marketplace.json format
• Need correct folder structure (.claude-plugin/plugin.json, skills/*/SKILL.md)
• Easy to misspell field names (allowed-tools? allowedTools?)
• Mistakes are hard to catch because agents still work with invalid config

Quick Start

// 1. Create a plugin
val plugin = Plugin.Builder(
    name = "my-plugin",
    description = "My plugin description",
    version = "1.0.0"
)
    .author(name = "Your Name")
    .addCommand(
        Command.Builder(
            name = "my-command",
            description = "What this command does",
            body = "# Command\n\nInstructions..."
        ).build()
    )
    .addSkill(
        Skill.Builder(
            name = "my-skill",
            description = "When to use this skill",
            body = "# Skill\n\nGuidance..."
        ).build()
    )
    .build()

// 2. Create marketplace (optional)
val marketplace = Marketplace.Builder(
    name = "my-marketplace",
    owner = Owner(name = "Your Name")
)
    .addPlugin(plugin)
    .build()

// 3. Write to disk
marketplace.writeClaudeCodeExtension(Path("output"))
// Or just the plugin: plugin.writeClaudeCodeExtension(Path("output"))

Generated Structure

output/my-marketplace/
├── .claude-plugin/
│   └── marketplace.json
└── plugins/
    └── my-plugin/
        ├── .claude-plugin/
        │   └── plugin.json
        ├── commands/
        │   └── my-command.md
        └── skills/
            └── my-skill/
                └── SKILL.md

API Reference

Skill.Builder(name, description, body)

• .license(license: String) - Set license
• .allowedTools(vararg tools: String) - Restrict tools
• .addMetadata(key, value) - Add custom metadata

Command.Builder(name, description, body)

• No optional fields currently

Plugin.Builder(name, description, version)

• .author(name: String) - Set author
• .addCommand(command: Command) - Add command
• .addSkill(skill: Skill) - Add skill
• .addHook(hook: HookMatcher) - Add hook

HookMatcher.Builder(event: HookEvent)

• .matcher(pattern: String) - Tool pattern (e.g., "Write|Edit")
• .command(command: String, timeout: Int?) - Add command hook
• .prompt(prompt: String, timeout: Int?) - Add prompt hook (LLM-based)

HookEvent: PreToolUse, PostToolUse, PermissionRequest, Notification, UserPromptSubmit, Stop, SubagentStop, PreCompact, SessionStart, SessionEnd

Marketplace.Builder(name, owner)

• .addPlugin(plugin: Plugin) - Add embedded plugin
• .addPlugin(name, source, ...) - Add external plugin reference
• .metadata(description, version, pluginRoot) - Set metadata

Run in Workspace

cd workspace
cp src/main/kotlin/Main.kt.template src/main/kotlin/Main.kt
# Edit Main.kt
./gradlew :workspace:run