Capabilities Manager

The capa CLI keeps a single source-of-truth file — capabilities.yaml (or .json) — that describes everything an agent can do in this project: skills, MCP servers, tools, hooks, sub-agents, rules, plugins, and per-provider files (AGENTS.md, CLAUDE.md). Editing that file and running the right capa command is the whole loop.

This skill is the routing layer for that loop. The actual command reference, schema, full YAML examples, and troubleshooting tables live in references/. Load the one you need rather than re-deriving its contents — they are kept up to date and are the authoritative source.

How capa works (one screen)

1. The file is the source of truth. capabilities.yaml declares what gets installed. Capa never auto-discovers anything from .claude/, .cursor/, etc. — if it's not in the file, capa won't manage it. (Onboarding an already-configured project is the bootstrap skill's job.)
2. capa install writes everything. Skill directories under each provider, MCP client config (.mcp.json, .cursor/mcp.json, etc.), AGENTS.md / CLAUDE.md blocks, hook entries, rules — all rewritten from the file. Anything labeled name: capa:<id> is capa's; entries the user authored by hand are left alone.
3. capa clean removes only what capa wrote. Safe to run; doesn't touch user-authored files or settings entries.
4. A background server at localhost:5912 handles credential prompts, tool execution (capa sh), and the MCP endpoints providers connect to. Started by capa install; lifecycle is capa start | stop | restart | status.
5. Secrets are ${VarName} placeholders anywhere in the file. Capa prompts for them via web UI on install, or loads from .env with capa install -e.

Routing — load the reference that matches the task

The references are sized for selective reads (each ≤ ~600 lines, with table-of-contents at the top of the larger ones). Don't load all four if only one applies.

Pitfalls worth heading off

These are the mistakes an agent makes when it improvises the YAML instead of consulting the schema. Skim them before writing or editing a capabilities file.

@ vs :: in def.repo

The repo string used by skills, rules, plugins, hook sources, and agent snippets has two grammars with different resolution semantics:

• owner/repo@<basename> — capa searches the repo recursively for an entry matching <basename> (a directory containing SKILL.md for skills, a file with that basename for rules / snippets). The right-hand side must have no slashes.
• owner/repo::<exact/path> — no search; the path must point exactly at the right thing from the repo root.

Use @ when the name is unique and stable. Use :: when the file location is part of what the user told you (e.g. "the file is at rules/typescript.md") or when collisions are possible. Both forms accept pinning: :v1.2.0 (tag/branch) or #abc1234 (commit SHA).

${VarName} is a capa placeholder, not a shell variable

${BraveApiKey} in capabilities.yaml is resolved by capa at install time from its credential store or a .env file. It has nothing to do with the runtime environment of any spawned process. In particular: providers do not export tool input as env vars to hooks — each fired hook receives a JSON payload on stdin. If a hook needs to inspect the command being run, write a local script that reads stdin with jq (see the hook example in references/capabilities-schema.md), not an inline command with ${...} placeholders expecting the command text to be interpolated.

Tool naming: @server.tool vs plain id

• MCP tools are referenced from skills as @server-id.tool-id (e.g. @brave.search). The @ distinguishes them from command tools.
• Command tools use the plain tool id (hello_world, deploy_service).
• In capa sh, both are slugified to kebab-case (@gitlab.list_merge_requests → capa sh gitlab list-merge-requests).

When binding tools to skills via requires:, mismatching the @ prefix is the #1 cause of "tool not found" at install time.

Tool exposure mode shapes everything downstream

options.toolExposure has three values and they change what capa install writes:

• expose-all (default): every tool any active skill requires shows up in the MCP tools/list. Simplest.
• on-demand: only setup_tools and call_tool are exposed at startup; the agent activates skills on demand. Keeps the active toolset small for long contexts.
• none: capa writes no project-local MCP config files at all. The agent is expected to invoke tools via capa sh <group> <tool> instead. Useful when policy forbids per-project .mcp.json edits.

Pick deliberately — switching modes later cleans up old entries on the next install but the choice colours the install output.

Conventions that prevent surprises

• Keep secrets out of the file. Always use ${VarName} placeholders; never paste literal API keys. Capa stores values per-project in ~/.capa/capa.db.
• Set requires: on every skill. Skills without requires: get no tools exposed under on-demand and clutter the install warnings under expose-all. The requires: list is also how capa wires the dependency graph.
• Prefer @ for skill repos, :: for rule / snippet paths. Skill basenames are usually unique inside a repo; rule files have known paths and you want the install to fail loudly if the file ever moves.
• Don't repeat the server name in tool ids. A tool under @gitlab should be id: search_projects, not id: gitlab_search_projects — capa already groups by server, so the prefix becomes noise (capa sh gitlab gitlab-search-projects).
• Test the install loop after every change. capa install is idempotent and surfaces every problem (missing CLI, blocked phrase, unreachable remote, OAuth probe failure). Run it; don't infer.

After making changes

Most edits follow the same cycle:

1. Edit capabilities.yaml.
2. capa install — installs/updates everything, prompts for any new credentials.
3. capa restart — only needed if you changed server commands, server env vars, or tool exposure mode. Skill content, rule content, hook bodies, and agents-block content all take effect on the next install without a restart.
4. Verify in the client (Cursor reloads; Claude Code reloads on next session start) or with capa sh <group> <tool> --help to confirm the tool is registered.

If an install fails or behaves unexpectedly, jump directly to references/troubleshooting.md — the symptoms there are indexed by what the user actually sees in the terminal.

References

External: CAPA on GitHub · skills.sh registry · MCP protocol