skill-groups

Organize AI-agent skills into named groups and mount them per project — the dotfiles of the AI skill world

中文 ·

Collect the skills you actually use into named groups (e.g. python, web, sql), declare which groups a project needs, and let one command mount the right skills into the right agent directory. Zero dependencies, works on Python 3.9+.

Why

Skill libraries grow fast. When your global store has 160 skills and every new project needs a different subset, you stop re-picking them by hand and start asking "which project already solved this?"

skill-groups gives you three layers instead of one pile:

Layer	Where it lives	What it holds
Global	SG_HOME (default ~/.sg)	every skill you've ever collected, cached by content
Group	SG_HOME/groups/<name>.json	a named, reusable bundle of skills with sources
Project	.sg.json + a skills dir	which groups this project mounts, and where

Projects stay portable because a project declares groups, not raw paths. The skills dir that gets mounted (.agents/skills, .claude/skills, ...) is a real agent-recognized location, so there is zero per-agent configuration: the agent already scans that directory. The group definitions and the cache live outside the project, so the project itself stays clean, and the mounts are re-creatable with one command.

Supported agents

Each agent already reads a conventional skills directory inside the project root. skill-groups just mounts skills into that directory, so it works with any agent that scans these paths.

Agent	Skills directory
Standard (Cursor, Gemini CLI, Copilot CLI, others)	.agents/skills
Claude Code	.claude/skills
Codex	.codex/skills
OpenCode	.opencode/skills

Pick the target with sg init --agent claude (choices: agents, claude, codex, opencode; default agents). --agent is repeatable — a project can mount into several agents at once: sg init --agent claude --agent opencode serves both .claude/skills and .opencode/skills from one declaration.

Claude Code users: you MUST run sg init --agent claude — Claude Code does not scan .agents/skills yet (tracked in anthropics/claude-code#16345); the default would silently load nothing. And after mounting, fully restart your agent — skills are registered at process start; a new session inside a long-running agent (e.g. /new in OpenCode) does not re-scan.

Install

The package is a zero-dependency Python 3.9+ CLI named sg.

pip install skill-groups

After install, sg is on your PATH and sg --help works from any directory.

Developers: from a clone of this repo, pip install -e . installs in editable mode (the build backend is hatchling; offline use pip install -e . --no-build-isolation).

Zero-install alternative: you don't have to install anything. From the repo root, python -m sg runs the same CLI directly, because the sg package is importable from the current directory. Every example below works with either sg ... or python -m sg ....

Quickstart

Run these in a new project directory. Expected output is shown below each command.

# 1. turn the current directory into a skill-groups project
sg init
# initialized C:\path\to\project

This writes .sg.json (schema v2) and adds the agent skills dir (.agents/skills by default) to your .gitignore. Use sg init --agent claude --agent opencode to serve several agents from one project; sg init --force --agent codex retargets an existing project (groups and standalone skills are kept).

# 2. create a group
sg group create python --description "Python tooling"
# created group python

# 3. add skills to the group from local folders
sg group add python lint --type local --path C:\path\to\lint-skill
# added lint to group python

sg group add python format --type local --path C:\path\to\format-skill
# added format to group python

# 4. mount every skill in the group into this project
sg use python
# used: python

# 4b. mount a standalone skill too (no group required)
sg use python --skill git-commit-writer --path "C:\path\to\git-commit-writer"
# used: python + git-commit-writer

--skill/--path can be repeated (they must come in pairs). Standalone skills are recorded in .sg.json under skills (group is ungrouped in sg ls) and are fully covered by sg status/sg sync/sg unuse --skill <id>.

# 5. see what's mounted
sg ls
# format (python, local)
# lint (python, local)

# 6. check status while the skills are mounted
sg status
# format (python): ok
# lint (python): ok

# 7. drop the group again (unmounts its skills)
sg unuse python
# unused: python

# 8. repair mounts to match the declaration
sg sync
# format: unchanged
# lint: unchanged

# 9. refresh git-sourced skills to their latest upstream
sg update
# lint: unchanged
# pytest: updated

sg status prints one line per mounted skill (skill (group): state, where state is ok, missing-link, drift, conflict, or stale), and sg sync repairs mounts to match the declaration (actions: unchanged, remounted, relinked, renewed, removed, skipped). Both exit 0; sg status --check exits 1 as soon as any skill is not ok — the hook for CI and pre-commit compliance checks. sg update re-fetches every git-source skill (branch/tag/default-branch revs; pinned commit shas and local sources are left alone), reporting updated when the resolved sha moved, and rewrites sg.lock accordingly.

Group definitions (schema v1)

A group is a JSON file at <SG_HOME>/groups/<name>.json. You can build it with sg group add, or write it by hand:

{
  "name": "python",
  "description": "Python tooling",
  "skills": [
    {
      "id": "lint",
      "source": { "type": "local", "path": "C:/skills/lint" }
    },
    {
      "id": "pytest",
      "source": {
        "type": "git",
        "repo": "owner/repo",
        "path": "skills/pytest",
        "rev": "main"
      }
    }
  ]
}

Rules enforced on every read:

• name is a non-empty string and may not contain / or \.
• Skill id must be unique within the group.
• local sources require a string path; git sources require a string repo (path and rev are optional).

Inspect your groups with sg group list and sg group show python. Remove a group (its definition file) with sg group rm python — note that projects whose .sg.json still declares the removed group will report unknown group on the next sg use/sg sync.

Cache and mount mechanism

Every skill is fetched once into a content-addressed cache, then mounted into the project. The flow is: group → source → cache → mount.

• Cache layout: <SG_HOME>/cache/<key>/<skill_id>/
• <key> is a 10-hex sha256 of the source identity. For git sources the requested rev is part of the identity, so asking for a new rev gets a fresh cache directory and a stale cache can never be served for the wrong rev.
• Local sources are copied on first fetch (gated by the presence of SKILL.md, so re-running is a no-op). Git sources are shallow-cloned once into <skill_dir>/.repo and reused on later calls.

Mounting happens in one of three modes, set with sg init --mode ...:

Mode	Behavior
auto (default)	Windows: junction, falling back to symlink, then copy. Other platforms: symlink, falling back to copy.
symlink	Always a directory symlink.
copy	Always a full copy.

When auto falls back to copy, it prints a warning to stderr (warning: fell back to copy for <skill_id>). Prefer junction/symlink over copy: copies go stale when the cached skill changes, and sg unuse has to delete real files instead of one link.

sg use is all-or-nothing. Before any mount it resolves every source and pre-flights every target link; if the same skill id is declared by two groups with different sources, or a target path already exists with different content, the whole batch aborts and nothing is changed.

Windows notes

• Junctions need no admin rights. mklink /J works in a normal user session, which is why auto tries junctions first on Windows.
• Symlinks need Developer Mode (Settings → Privacy & Security → For developers → Developer Mode) or an elevated shell. If a symlink can't be created, auto silently falls back to a copy.
• Paths with spaces are safe. All git and mount commands use subprocess list form, never shell string concatenation, so a repo path like C:\My Skills\repo works.
• Unmounting never touches the target: junctions are removed as reparse points (os.rmdir / cmd /c rmdir), never with a recursive delete.

Exit codes

Code	Meaning	Example
0	Success	any command that completes
1	User error: bad input, conflicts, unknown group	error: group already exists: python
2	Environment error or unexpected failure; also CLI usage errors	error: git not found on PATH, unknown command

User errors print error: <message> to stderr and leave your state untouched. Environment errors (missing git, unwritable cache, corrupt config) print the same way but signal a setup problem, not an input problem.

Git sources

sg group add web serve --type git --repo owner/repo --path skills/web --rev v1
# added serve to group web

• repo accepts an owner/repo shorthand (resolved to https://github.com/<owner/repo>.git), a full URL, or a local repository path.
• path selects a subdirectory of the repo as the skill content; omit it to use the repo root.
• rev accepts a branch name, a tag, or a full 40-character commit sha. A branch/tag becomes a shallow --branch clone; a sha is fetched and checked out directly.
• The lock (sg.lock) records the actual resolved HEAD in resolved_sha, so sg status can later tell you whether the mounted skill matches what the declaration resolved to.
• sg update refreshes branch/tag/default-branch sources in place (fetch first, so a network failure leaves your mounts untouched); a pinned sha is immutable by definition and never refreshed.

Troubleshooting: sg doctor

sg doctor reports the environment, which is the first stop when a git source won't fetch or a mount fails:

> sg doctor
python: 3.13.3
git: available
sg_home: C:\Users\me\.sg
sg_home_writable: yes
junction: supported

Line	Healthy	If not
git	available	install git and put it on PATH; git sources cannot fetch without it
sg_home	your expected home path	set SG_HOME to redirect all global state, e.g. $env:SG_HOME="$env:TEMP\sg-test" in PowerShell
sg_home_writable	yes	fix permissions on SG_HOME; the cache and groups live there
junction	supported on Windows	mounts fall back to symlink/copy automatically

The default SG_HOME is ~/.sg. Its layout: config.json (global config), groups/ (group definitions), cache/ (fetched skills).

Development

python -m unittest discover tests -v

The suite runs 236 tests covering the CLI surface, group validation, caching, git sources, updating, mounting, multi-agent projects, standalone skills, and isolation.

License

MIT