coding-agent-extension-builder

takahirom's avatarfrom takahirom

Generate Claude Code plugins, skills, and marketplaces using Kotlin DSL.Use when the user wants to:- Create a new plugin with commands and skills- Create a marketplace to distribute plugins- Generate correct folder structure (.claude-plugin/, skills/, commands/)- Avoid mistakes in JSON format and YAML front matter field names

⭐0stars🔀0forks📁View on GitHub🕐Updated Jan 9, 2026
[Prompt Templates and Packaging]

When & Why to Use This Skill

The coding-agent-extension-builder is a specialized Kotlin DSL designed to streamline the development of Claude Code plugins, skills, and marketplaces. It provides a type-safe environment to generate standardized folder structures and configuration files, effectively eliminating common manual errors in JSON formatting and YAML front matter while accelerating the deployment of agentic capabilities.

Use Cases

  • Scenario 1: Rapidly scaffolding new Claude Code plugins with predefined commands and skills, ensuring all metadata and directory requirements like '.claude-plugin/' and 'SKILL.md' are met automatically.
  • Scenario 2: Establishing and managing a centralized marketplace to distribute custom agent extensions across teams, ensuring consistent versioning and authorship tracking.
  • Scenario 3: Enhancing development reliability by using compile-time safety to validate tool permissions, licenses, and complex hook configurations (like PreToolUse or SessionStart) before generating the final extension package.
namecoding-agent-extension-builder
description|
licenseMIT
allowed-toolsRead, Write, Edit, Bash, Glob, Grep

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