nul-skills

Northwestern University Libraries community AI skills catalog. This repository is a Claude Code plugin marketplace and is also consumed by nul-cli, which extracts the SKILL.md files out of each plugin and installs them for non-Claude AI assistants (Codex, ChatGPT, Cursor, …).

Two install paths for skills:

• Claude Code users — /plugin marketplace add nulib-labs/nul-skills then /plugin install <plugin>@nul-skills. Skills become /<plugin>:<skill>.
• Other agents — nul skills add <plugin> writes each skill to .agents/skills/<plugin>-<skill>/SKILL.md.

Layout

nul-skills/
├── .claude-plugin/
│   └── marketplace.json                     # catalog (Claude convention)
├── plugins/
│   └── <plugin-name>/
│       ├── .claude-plugin/
│       │   └── plugin.json                  # plugin manifest
│       └── skills/
│           └── <skill-name>/
│               └── SKILL.md
└── README.md

Each plugin can ship one or more skills. A plugin may also include commands/, agents/, hooks/, .mcp.json, etc. — those are Claude Code-specific and are ignored by nul-cli, which only installs the SKILL.md files. See Claude Code's plugins reference for the full plugin schema.

Adding a Plugin

1. Create the plugin directory:

   plugins/<plugin>/
     .claude-plugin/plugin.json
     skills/<skill>/SKILL.md
   

2. Fill in plugin.json:

   {
     "name": "<plugin>",
     "description": "What the plugin does.",
     "author": { "name": "Northwestern University Libraries" }
   }

   Omit version to let updates flow on every commit (Claude Code uses the commit SHA at the plugin's path); set version if you want explicit release gating.
3. Write skills/<skill>/SKILL.md with a description: front-matter that explains when Claude (or another agent) should invoke it.
4. Add an entry to .claude-plugin/marketplace.json under plugins:

   {
     "name": "<plugin>",
     "source": "./plugins/<plugin>",
     "description": "One-line summary."
   }

5. Open a PR. No catalog version bump required — nul-cli upgrades each installed skill when its plugin's path gets a new commit.

Validation

Run Claude Code's plugin validator from the repository root before opening a PR:

claude plugin validate .

Expected output:

Validating marketplace manifest:
/example/path/nul-skills/.claude-plugin/marketplace.json

✔ Validation passed

Naming guidance

Inside Claude Code, skills are namespaced as /<plugin-name>:<skill-name>. So plugins/meadow/skills/run-tests/SKILL.md becomes /meadow:run-tests. Pick the inner skill name to read well after the colon. For non-Claude clients, nul-cli installs each skill at .agents/skills/<plugin-name>-<skill-name>/ to avoid collisions between plugins.

Versioning

nul-cli skills upgrade calls GET /repos/nulib-labs/nul-skills/commits?path=plugins/<plugin> and compares the resolved SHA against the manifest stamped at install time. Any commit that touches the plugin's path triggers an upgrade for every installed skill from that plugin.

The metadata.version field in marketplace.json is informational only.

Local Development with nul-cli

export NUL_SKILLS_PATH=/path/to/nul-skills
nul skills list
nul skills add meadow --dest=/tmp/agents
# installs /tmp/agents/meadow-run-tests/

Without NUL_SKILLS_PATH, nul-cli fetches from nulib-labs/nul-skills. Override the source via NUL_SKILLS_REPO and NUL_SKILLS_REF.