Weft Core

weft /wɛft/ (n.) — in weaving, the thread carried across and woven through all the warp threads to make the cloth. Here: one capability, woven across every coding-agent harness.

A cross-harness agent-plugin framework: author once, compile to every coding-agent harness, with built-in evals and trust.

Every coding-agent harness now supports roughly the same extension primitives (skills, MCP servers, sub-agents, hooks, commands) bundled as a plugin and distributed through a marketplace. This includes Claude Code, OpenAI Codex, Cursor, GitHub Copilot, and OpenCode. But each harness has its own manifest format and marketplace mechanics. Shipping one capability to all of them today means hand-writing several manifests, submitting to several catalogs, and keeping versions in sync by hand, with no standard way to test a component or signal that it is trustworthy.

Weft is a compiler plus conventions (not a hosted platform) that fixes this:

• You author a plugin once, in each component's most upstream-standard format (SKILL.md, MCP server.json, ...).
• weft build compiles the plugin to every harness's native manifests and the marketplace catalog, with no hand-written JSON.
• Distribution stays git-first. An optional metadata-only index can federate existing marketplaces (notably the official MCP Registry).
• Evals and trust badges are first-class artifacts that live in the plugin repo and gate publishing.

Quickstart

pnpm install
pnpm build                       # compile all packages
weft init my-plugin              # scaffold weft.yaml + a sample skill
weft validate my-plugin          # static validation (the "valid" badge)
weft build my-plugin --out out   # compile to harness manifests
weft install my-plugin --scope project   # place files + write weft.lock

During development the CLI runs straight off TypeScript source via Bun:

bun packages/cli/src/index.ts validate fixtures/sample-plugin

Status

All four phases are implemented and tested (212 tests, ~92% coverage). A plugin compiles to every harness's native manifests with zero hand-written JSON, passes claude plugin validate --strict, installs with a content-addressed weft.lock, and is proven end-to-end against a real headless Claude (see the demo).

• Phase 0: the compile loop (Claude Code).
• Phase 1: all five adapters plus @michaelfromyeg/weft-eval (real headless drivers, honest UNTESTED, Copilot trace->output degradation), plus remote resolver, dependencies, secrets, weft update.
• Phase 2: @michaelfromyeg/weft-index (build + MCP-Registry federation), valid/tested badges, the weft publish deterministic gate plus a CI action.
• Phase 3: judge + differential evals + baselines, security scan, ed25519 signing (signed badge), and managed-mode install gating.

See docs/roadmap.md for the per-criterion acceptance status.

Documentation

• Concepts: start here, plugin vs marketplace.
• Demo: real-world use cases, end to end (bash examples/demo.sh).
• Getting started: a full CLI walkthrough.
• CLI reference: a generated map of every command (weft docs).
• Architecture: the compile pipeline, packages, and the adapter seam.
• Authoring plugins: the weft.yaml / marketplace.yaml / cases.yaml reference.
• Writing an adapter: the public contract a community adapter implements.
• Harness research: verified facts per harness (mid-2026).
• Roadmap: phased build plan and acceptance status.

Repository layout

packages/
  schema/          @michaelfromyeg/weft-schema       Zod schemas + types + JSON-Schema export
  core/            @michaelfromyeg/weft-core         compile pipeline, resolver, deps, secrets, lockfile,
                                      signing, managed-mode, namespacing
  adapter-kit/     @michaelfromyeg/weft-adapter-kit  public HarnessAdapter/Driver interfaces + helpers
  adapter-claude/  @michaelfromyeg/weft-adapter-claude   (+ codex, cursor, copilot, opencode)
  eval/            @michaelfromyeg/weft-eval         headless drivers + runner + judge/differential + baselines
  index/           @michaelfromyeg/weft-index        metadata index, MCP-Registry federation, badges, publish gate
  cli/             @michaelfromyeg/weft-cli          the `weft` binary (thin shell over the above)
fixtures/
  sample-plugin/                      end-to-end test plugin (1 skill + 1 mcp + evals)
  sample-marketplace/                 a 2-plugin marketplace
examples/
  demo.sh                             runnable end-to-end demo

Toolchain

TypeScript (strict), developed with Bun, shipped Node-compatible (published packages use only node:* APIs). pnpm workspaces, Vitest, Biome, changesets, tsup. The standalone binary is produced with bun build --compile.

License

MIT