The universal scaffold for coding-agent plugins. One repository, five harnesses, skills that own their runtime.

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Harness Alchemist scaffolds one TypeScript plugin repository that installs natively into Claude Code, Codex/ChatGPT, OpenCode, Google Antigravity, and DeepSeek Harness/Cordis. Each product skill declares its fixed executable and portable tool schema in skill-runtime.json; host entrypoints delegate through @lunarmoon26/agent-skill-runtime.

Install

npm install -g harness-alchemist
# or run it without installing:
npx harness-alchemist@latest create my-plugin --help

The CLI implementation is a native Rust binary. npm and Bun installations use a small launcher to select a prebuilt macOS, Linux, or Windows binary for x64 or arm64. No Rust toolchain or install script is required by CLI users. Repository development requires the pinned Rust toolchain in rust-toolchain.toml. The npm launcher requires Node.js 22.20+; invoking it with Bun 1.2+ is also supported.

Quick start

npx harness-alchemist@latest create my-plugin \
  --description "What the plugin does" \
  --author "Example Team" \
  --repository example/my-plugin

cd my-plugin && npm install && npm run verify

Creation only writes to a missing or empty destination. The generated project passes its own gate out of the box: TypeScript checks, runtime delegation tests, scaffold validation, and an npm-payload audit.

Existing monorepos and SDK packages

validate also supports an adapted plugin package inside an existing repository. Add alchemy.json at the repository root:

{
  "$schema": "https://unpkg.com/harness-alchemist/alchemy.schema.json",
  "pluginRoot": "packages/my-sdk",
  "opencodeExport": "./server"
}

The manifest is JSON-Schema-validated; the schema ships in the npm package and is referenced through $schema, so editors autocomplete and check every field.

pluginRoot contains the canonical plugin manifests, shared skills, Cordis patch, adapter sources, and publishable package metadata. Repository marketplace manifests remain at the project root and point at that package directory. opencodeExport: "./server" preserves an SDK at the package root while exposing the OpenCode adapter through the modern server entrypoint. Omitting the file retains the strict generated single-package layout.

The optional runtime field selects what the adapted package must contain:

• "npm" (default) — the full generated contract: npm metadata, portable runtime manifests, OpenCode and Cordis adapters, and the Cordis patch.
• "skills" — skills, portable runtime manifests, and harness manifests only. No npm package, adapters, or Cordis patch are required, and single-language scripts are allowed, so Python, Go, Rust, Java, C#, or Swift repositories can expose their workflows to Claude Code, Codex, Antigravity, and DeepSeek's filesystem skill roots without adopting a JavaScript runtime.

Generated projects include a alchemy.json manifest recording their runtime, canonical template version, generator, generatorVersion, and createdAt; npm run sync keeps generatorVersion aligned with the package version.

What you get

Surface	Purpose
skills/<name>/	Agent Skills workflow, portable skill-runtime.json, fixed executable, optional tested twin, and tool-contract reference
src/opencode.ts	OpenCode plugin projecting the portable runtime manifest as native tools
src/deepseek.ts + cordis.patch.yml	Cordis function plugin registering the same portable tools
.claude-plugin/, .codex-plugin/, .agents/plugins/, plugin.json, mcp.json	Native and Agent Plugins manifests for Claude Code, Codex, Antigravity, and MCP hosts
.agents/skills/develop-<name>/	Repository-maintenance skill so agents can develop the project recursively
.github/workflows/	CI plus tag-triggered publish (vX.Y.Z → verify → npm provenance)

Supported harnesses

Install paths below are verified against real CLIs before shipping in the template.

Harness	Skills	Runtime	Install
Claude Code	bundled natively	—	claude plugin install <name>@<marketplace>
Codex/ChatGPT	bundled natively	—	codex plugin add <name>@<marketplace>
OpenCode	via ~/.agents/skills/	npm package plugin	"plugins": ["<package>"] in opencode.json
Google Antigravity	nested bundle	—	agy plugin validate . && agy plugin install .
DeepSeek Harness	profile filesystem roots	Cordis tool plugin	dsh plugin --profile demo add <package-or-path>

Skill script contract

Product skills own their logic; adapters never do.

skills/<name>/skill-runtime.json declares the model-facing schema and selects one author-controlled entrypoint. Hosts validate the same manifest and never accept an executable path from model input.

echo '{"request": "hello"}' | node skills/<name>/scripts/main.mjs
# {"ok":true,"plugin":"my-plugin","echo":{"request":"hello"}}

• One JSON object on stdin, one JSON result plus newline on stdout.
• Non-zero exit with a stderr diagnostic on failure.
• scripts/main.py is a stdlib-only behavioral twin for direct compatibility testing; the starter manifest selects scripts/main.mjs for host tools.

Install-level verification

install-check drives your local harness CLIs against the project and asserts each one can discover the plugin — the same checks a user's install would perform, automated and cleaned up afterwards:

npx harness-alchemist@latest install-check /path/to/project
npx harness-alchemist@latest install-check . --harness agy --json

Harness	Verified by	Isolation
Claude Code	marketplace add → install → plugin details skill inventory	user scope, auto-removed
Codex	marketplace add → plugin add → plugin list enabled	plugin cache, auto-removed
Antigravity	plugin validate → install → plugin list	staged, auto-uninstalled
OpenCode	skills discovery via debug skill + plugin startup	temp XDG_CONFIG_HOME
DeepSeek	Cordis bundle composed into profile (--dump-config)	temp DSH_HOME

Claude, Codex, and Antigravity run in both runtimes; the OpenCode plugin leg and the DeepSeek Cordis check require npm mode with built adapters (npm run build first). Missing CLIs are reported as skipped, not failures.

Validation tiers

npm run validate always enforces Agent Skills frontmatter compliance, SKILL.md reference resolution, validation of every present runtime manifest, fixed contained entrypoints, npm-mode twin parity, and Python syntax through the native Rust parser. Generated npm plugins require a runtime manifest for every product skill; adapted skills-only repositories may also contain additional prose-only skills while retaining a manifest for the primary MCP-targeted skill. The validator does not execute project Python during structural validation; JavaScript/Python behavioral parity is exercised by the runtime tests.

Release automation

The main package and six platform packages use GitHub Actions workflow npm-publish.yml in lunarmoon26/harness-alchemist as their Trusted Publisher. The workflow builds each native target on its matching hosted runner, publishes platform packages first, then publishes the main package. It uses OIDC instead of an NPM_TOKEN, requires the tag to match both package.json and Cargo.toml, and accepts only commits contained in main.

Trusted Publisher configuration is package-scoped. Before the first native release, create each new platform package once using an interactive npm session with 2FA (a reserved 0.0.0 bootstrap version keeps real releases on OIDC), then configure its publisher with npm 11.5.1 or newer:

npm trust github @lunarmoon26/harness-alchemist-darwin-arm64 \
  --repo lunarmoon26/harness-alchemist --file npm-publish.yml \
  --allow-publish --yes

Repeat that command for all six platform package names, then set each package's publishing access to Require two-factor authentication and disallow tokens. The existing main package must retain the same workflow identity and policy. Prerelease versions publish under the next dist-tag; stable versions publish under latest.

# bump package.json version, then:
npm run sync && npm run verify && git commit -am "Release vX.Y.Z" && git push
# after the release commit is merged to main:
git tag vX.Y.Z && git push origin vX.Y.Z   # publishes through npm Trusted Publishing

License

MIT