Packsmith

A zero-dependency Grok Bot / Agent plugin (stdio MCP server + one skill) that installs and manages skill packs for Grok Bots. It moves the capacity limit off the install template and onto a hash-pinned pack you host yourself, so a bot can carry far more skills than the template size cap allows — and it does not depend on the UpdateSkill tool.

A skill is installed by writing <workflows>/<slug>/SKILL.md (markdown with name + description frontmatter). The default workflows root is /home/box/agent-data/workflows, overridable with PACKSMITH_ROOT (used by the tests so they never touch the real dir).

Data shapes

• Pack: { "version"?: string, "skills": { "<kebab-slug>": "<SKILL.md text>" } }. A legacy flat map { "skills/<slug>/SKILL.md": "<text>" } (or { "<slug>": "<text>" }) is also accepted.

• Manifest (<workflows>/.packsmith.json): [{ url, sha256, version, skills[], installedAt, sealed? }].

Related MCP server: pmcp

Tools

Content is never executed. Packs are data: Packsmith only writes SKILL.md text.

Encryption format

seal_pack/unseal_pack are byte-compatible with:

openssl enc -aes-256-cbc -pbkdf2 -iter 200000 -pass env:PASS

(Salted__ + 8-byte salt + AES-256-CBC, key/iv via PBKDF2-SHA256, 200k iterations). Pass the passphrase via env PACKSMITH_PASSPHRASE (preferred) or the passphrase arg — it is never logged or returned.

Safety

• https-only (set PACKSMITH_ALLOW_HTTP=1 for tests), optional host allowlist via PACKSMITH_ALLOWED_HOSTS.

• Slugs are kebab-case only — path-traversal guard. Frontmatter must contain name and description.

• Size limits: PACKSMITH_MAX_PACK_BYTES (1 MiB), PACKSMITH_MAX_SKILL_BYTES (64 KiB), PACKSMITH_MAX_SKILLS (100).

• No network beyond the exact URL given; redirects are not followed. sha256 mismatch = refuse, no write.

Publishing a pack (user-side)

1. build_pack(["my-skill-a","my-skill-b"], "1") → a pack JSON file + sha256.

2. Upload the JSON to any static host — e.g. Cloudflare Pages, GitHub Pages, S3, or your bot hub.

3. Share the URL + sha256. Recipients run install_pack(url, sha256). For a private drop, seal_pack first and share the passphrase out of band; recipients run unseal_pack.

Run

node src/server.js        # stdio MCP server
npm test                  # node --test (unit + live)

Layout

plugin.json  mcp.json  package.json  README.md
src/core.js  src/server.js
skills/packsmith-guide/SKILL.md
test/unit.test.js  test/live.test.js

Transport note

Packsmith ships as a local stdio MCP server (node src/server.js, zero dependencies). mcp.json follows the Agent Plugins standard (${PLUGIN_ROOT}); mcp.cursor.json is the Cursor variant (${CURSOR_PLUGIN_ROOT}). Hosts that only accept remote (HTTP/SSE) MCP servers will need a hosted endpoint; that is not provided yet.

License

MIT