Introduction

When developing agent plugins, you often need to adapt to the formats of different platforms such as Claude Code, Codex, OpenCode, Google Antigravity, and DeepSeek Harness/Cordis. Manually maintaining multiple configuration sets and structures is very cumbersome. The philosophy of DeepSeek Harness (DSH) is “everything is a plugin,” and developers need a tool to uniformly generate code repositories that conform to the specifications of each platform.

What Is It

harness-alchemist is a TypeScript plugin repository scaffold maintained by lunarmoon26. It implements the concept of “one codebase, five Harnesses”: the generated repository can be natively installed on the five platforms mentioned above. Its core is to give Skills their own runtime, declaring contracts through skill-runtime.json, rather than having host adapters write the logic. The project follows the MIT License.

Core Features

  1. Automatic scaffolding: Generates a TypeScript plugin repository, including the entry files and configuration required by each platform.
  2. Structure validation: After generation, it automatically runs TypeScript checks, runtime delegation tests, scaffolding validation, and npm package audit.
  3. Manifest generation: Automatically generates manifest files such as skill-runtime.json and alchemy.json.

Installation and Activation

The CLI tool is a native Rust binary and can run without users installing a Rust environment. npm and Bun installation methods use a lightweight launcher, but the launcher itself requires Node.js 22.20+ or Bun 1.2+.

The installation command is as follows:

npm install -g harness-alchemist

After installation, you can run it directly with npx without global installation:

npx harness-alchemist@latest create my-plugin --help

Typical Usage

  1. Create a plugin project:
    Specify the project description, author, and repository URL.
    npx harness-alchemist@latest create my-plugin \
      --description "What the plugin does" \
      --author "Example Team" \
      --repository example/my-plugin
  1. Install dependencies and verify:
    Enter the project directory, install dependencies, and run the built-in verification process.
    cd my-plugin && npm install && npm run verify
  1. Code validation:
    Run npm run validate to enforce Agent Skills frontmatter compliance checks, SKILL.md reference resolution, and runtime manifest validation.

Configuration and Structure

The generated project contains the following key structures:

  • skills/<name>/: Stores Agent Skills workflows, portable skill-runtime.json, fixed execution entry points, and tool contract references.
  • src/opencode.ts: OpenCode plugin entry point, which projects the portable runtime manifest into native tools.
  • src/deepseek.ts + cordis.patch.yml: Cordis function plugin entry point, registering the same portable tools.
  • Manifests: skill-runtime.json defines the model-facing Schema and selects the execution entry point; alchemy.json records the runtime mode, template version, and generation time.

The project supports two runtime modes:
* npm (default): Includes the complete generated contract, npm metadata, portable runtime manifest, adapters, and Cordis patch.
* skills: Includes only Skills, runtime manifest, and Harness manifest. Suitable for Python, Go, and other language repositories that do not require an npm package and JavaScript runtime.

Supported Platforms

The plugins generated by this scaffold can be installed on the following Harnesses:

  • DeepSeek Harness: Installed through the profile filesystem root and Cordis tool plugins.
  • Claude Code: Natively installed through the marketplace manifest.
  • Codex/ChatGPT: Natively installed through the marketplace manifest.
  • OpenCode: Installed through ~/.agents/skills/ and configured in opencode.json.
  • Google Antigravity: Installed through nested packages.

Notes

Plugins run with the permissions of the current DSH process. Before installing or using a plugin, be sure to check the source code to confirm its security and licensing requirements.

Summary

harness-alchemist lowers the barrier for multi-platform agent plugin development through a single TypeScript repository specification. Developers can focus on the Skill logic itself, while leaving adaptation and validation to the scaffold.