plugin-skill

# Claude Code Skills Development Reference for developing effective skills. ## Arguments Run a check against a skill path in `$ARGUMENTS`, defaulting to the skill you just edited: - `--validate`: run `skill-lint` (see [Validation](#validation)) for frontmatter, naming, and reference-depth validation. - `--structure`: run the directory-structure check (`${CLAUDE_SKILL_DIR}/scripts/check-structure.ts`) for the SKILL.md, `scripts/`, `references/`, `assets/` layout. With neither flag, use the skill as an authoring reference. See [Validation](#validation). ## Skill Structure ```yaml --- name: plugin-name:skill-name description: Third-person capability description with trigger terms argument-hint: "[--flag] [<positional>]" allowed-tools: [Read, Grep, Glob] model: sonnet effort: low context: fork agent: Explore background: false user-invocable: false hooks: PreToolUse: - matcher: "Bash" hooks: - type: command command: "./scripts/validate.sh" once: true --- ``` #### Required Fields - `name`: Lowercase letters, numbers, hyphens only (max 64 chars). See [Naming](#naming). - `description`: Third-person, includes trigger terms and use cases (max 1024 chars). #### Optional Fields - `argument-hint`: Arguments the skill accepts, shown in the slash menu after the skill name. See [Argument Hints](#argument-hints). - `allowed-tools`: Tools Claude can use without permission when skill is active - `model`: Override the conversation's model. Prefer a tier alias (`haiku`, `sonnet`, `opus`, `fable`) or `inherit` over a dated model ID. - `effort`: Reasoning effort while the skill is active, applied only when typed as a slash command. Model invocation ignores it. Defaults to the conversation's effort. See [Reasoning Effort](references/patterns.md#reasoning-effort) for levels and cache cost by model. - `context`: Set to `fork` to run in isolated subagent context - `agent`: Agent type when `context: fork` (`Explore`, `Plan`, `general-purpose`, or custom) - `background`: Only with `context: fork`. `false` waits for the fork's result in the invoking turn instead of backgrounding it. Default `true`. - `user-invocable`: Hide from slash menu when `false` (default: `true`) - `disable-model-invocation`: Block model (Skill-tool) invocation and drop the skill's name and description from the always-on catalog (zero recurring context cost); still slash-invocable. Opposite of `user-invocable: false`, which hides the slash menu but keeps the description loaded for the model. - `hooks`: Skill-scoped hooks (`PreToolUse`, `PostToolUse`, `Stop`) #### Naming Plugin skills use `plugin-name:skill-name` with a colon namespace (e.g., `gitlab:ci`, `things:url`). The part after the colon should not repeat the plugin name. Skip the prefix when name equals plugin name. For standalone skills, use gerund form (verb + -ing): `processing-pdfs`, `analyzing-data`. Avoid vague names like `helper`, `utils`. #### Storage `~/.claude/skills/` (personal), `.claude/skills/` (project), plugins (bundled) ## Skill Authoring Best Practices Load the `prompting` skill before writing a skill body or a reference file. It carries the rules for every document a model executes. The sections below cover what changes when that document is a Claude Code skill. #### Descriptions The `description` field is the pointer Claude scans to decide whether to activate the skill. Write it for the model and make it slightly pushy, since under-triggering is the common failure. The wording rules are in the `prompting` skill. List triggers: the requests that call for the skill. End with the boundary to any sibling skill a request could land on. Tools, techniques, and capabilities go in the body. ```yaml description: Use when timing a program or command, asking whether a change or version made it faster, or building a benchmark harness. For repeated optimization toward a target, use performance:hill-climb. ``` #### Gotchas The highest-signal content in any skill is a `## Gotchas` section documenting failure modes hit in practice. Grow it as edge cases surface. #### Progressive Disclosure A skill is a folder. Keep `SKILL.md` a concise hub and push details into `references/`, `scripts/`, and `assets/`. Tell Claude what files exist and when to read them. Organize references by domain. A question about one domain then loads only that file. A model-invocable skill's `description` costs tokens in every session. Keep an invoked skill's body under roughly 4k tokens, since it is re-injected in full at every compaction. A `references/` file costs nothing until its pointer fires. Split one skill into two by invocation when the branches need different frontmatter: a different `model`, different `allowed-tools`, or one branch routed by the model while the other stays user-invoked. #### First-Run Setup Skills that depend on user-specific context should check for a `config.json` in `${CLAUDE_SKILL_DIR}` or `${CLAUDE_PLUGIN_DATA}`. If missing, prompt the user for setup and store answers for future runs. #### Store Persistent Data in `${CLAUDE_PLUGIN_DATA}` Skills can maintain state across runs: append-only logs, JSON records, SQLite databases. Use `${CLAUDE_PLUGIN_DATA}` for storage that survives plugin upgrades. #### Give Claude Code to Compose Include helper scripts and libraries that Claude can import and compose on the fly. Document scripts with `"Run script.py"` (execute) vs `"See script.py"` (reference). #### On-Demand Hooks Skill-scoped hooks activate only when the skill is invoked and last for the session. Use these for guardrails that would be annoying globally but valuable in specific contexts (e.g., blocking destructive commands during prod operations). ## Content Features ### String Substitutions | Variable | Description | | :---------------------- | :------------------------------------------------------------------------------- | | `$ARGUMENTS` | All arguments passed when invoking the skill. Appended automatically if absent. | | `$ARGUMENTS[N]` / `$N` | Access a specific argument by 0-based index. | | `${CLAUDE_SESSION_ID}` | Current session ID. | | `${CLAUDE_SKILL_DIR}` | Absolute path to the skill's directory. Substituted in skill content: the body, `!` injection commands, and `allowed-tools`. | These substitutions apply to skill content, not the frontmatter `hooks:` block. The hooks engine expands only `${CLAUDE_PROJECT_DIR}`, `${CLAUDE_PLUGIN_ROOT}`, and `${CLAUDE_PLUGIN_DATA}` ([hooks reference](https://code.claude.com/docs/en/hooks)); `${CLAUDE_SKILL_DIR}` there resolves to an empty string. In a hook command, reference a bundled script by plugin root instead: `${CLAUDE_PLUGIN_ROOT}/skills/<skill>/scripts/check.ts`. ### Argument Hints `argument-hint` declares the arguments a skill accepts. It renders in the slash menu after the skill name and reminds the user which flags exist. Give every directable skill a hint, even when it usually runs with none. A skill that branches internally ("if the user wants X") should expose that branch as a flag. #### Notation - Required tokens use angle brackets, optional tokens use square brackets: `<doc-path> [--draft]`. - Mutually-exclusive alternatives are pipe-separated with surrounding spaces: `[staged | <range> | HEAD]`. - Boolean flags are `[--flag]`. Value flags are `[--flag value]`. Enumerated values pipe-join without inner spaces: `[--role author|reviewer]`. - Order tokens as required positionals, then optional positionals, then flags. #### Parsing A skill that declares an `argument-hint` must parse `$ARGUMENTS` (or `$0`/`$1` for positionals) and act on what it finds. Add an `## Arguments` section to the body mapping each token to its behavior, with a stated default for every flag so the no-argument invocation stays well-defined. ### Dynamic Context Injection The bang-backtick syntax runs shell commands **before** the skill content is sent to Claude. The output replaces the placeholder — Claude sees only the result, not the command. This is preprocessing, not something Claude executes. Use it to inject live data (git state, CLI output, file contents) so the harness extracts and runs the commands without waiting on the model. See [references/patterns.md](references/patterns.md) for syntax, examples, and gotchas. ## Directory Structure Skills follow the [Agent Skills](https://agentskills.io/specification#optional-directories) directory convention. Only `SKILL.md` is required; all directories are optional. ``` skill-name/ ├── SKILL.md # Required: instructions and frontmatter ├── scripts/ # Executable code agents can run (self-contained, explicit errors) ├── references/ # Documentation loaded on demand (focused, domain-named files) └── assets/ # Static resources (templates, images, data files) ``` A PostToolUse hook validates writes to skill directories against this structure. ### File Naming Reserve ALL CAPS for files with special meaning (`SKILL.md`, `README.md`). Use lowercase for all other files. Keep references one level deep. ## Validation A skill-scoped PostToolUse hook runs `skill-lint` automatically when SKILL.md files are edited. For manual checks, run `bun run skill-lint path/to/skill/` from the project root. ## References Load the guide that covers the question at hand: - **[references/patterns.md](references/patterns.md)** - Dynamic context injection, subagent integration, reasoning effort, skill-scoped hooks, anti-patterns - **[references/troubleshooting.md](references/troubleshooting.md)** - Activation issues, plugin cache ## Resources - [Agent Skills Specification](https://agentskills.io/specification) - [Claude Code Skills](https://code.claude.com/docs/en/skills) - [Agent Skills Best Practices](https://docs.anthropic.com/en/docs/agents-and-tools/agent-skills/best-practices)