skill-builder

name	skill-builder
description	Builds a new Claude Code skill from scratch through a relentless, evidence-based interview that walks the skill's design tree decision-by-decision — entity fit, use cases, name, description, workflow steps, tools, and progressive-disclosure layout — then reviews the finished skill against the plugin-building guidance and applies every fix it finds. Use when creating, authoring, scaffolding, designing, or drafting a new skill or slash command. Does not build an agent or subagent — use agent-builder. Does not serve, vendor, or refresh the authoring guidance itself — use guidance.
allowed-tools	Read, Write, Edit, Glob, Grep, Bash(find *), Bash(mkdir *)

Guidance Location

The authoritative skill-authoring guidance ships in this plugin. Read the specific document a decision needs, when that decision is on the table — never read them all up front, because that defeats progressive disclosure and burns context on guidance the current skill does not touch.

• Plugin-building guidance root: ${CLAUDE_PLUGIN_ROOT}/skills/guidance/references/
• Skill-specific guidance: ${CLAUDE_PLUGIN_ROOT}/skills/guidance/references/skill-building-guidance/

Map from decision to governing document (read just-in-time):

Decision on the table	Read
Skill vs. agent vs. hook	plugin-entity-taxonomy.md
Use cases, trigger phrases, test cases	skill-building-guidance/use-case-planning.md
Directory name, file name, dependency prefix	skill-building-guidance/naming-conventions.md
The description field (four components, boundaries)	skill-building-guidance/skill-description-frontmatter.md, skill-building-guidance/skill-description-length.md
Which frontmatter fields to set	skill-building-guidance/skill-frontmatter-fields.md
Where content lives (body vs. references vs. scripts vs. assets)	skill-building-guidance/progressive-disclosure.md, skill-building-guidance/skill-reference-files.md
Step structure and workflow shape	skill-building-guidance/workflow-patterns.md, skill-building-guidance/writing-effective-instructions.md
allowed-tools, Bash permission granularity	skill-building-guidance/allowed-tools-bash-permissions.md, skill-building-guidance/allowed-tools-AskUserQuestion.md
Reading config / runtime data	skill-building-guidance/context-injection-commands.md, skill-building-guidance/dynamic-project-discovery.md
Running scripts	skill-building-guidance/script-execution-instructions.md
Dispatching agents from the skill	skill-building-guidance/agent-dispatch-namespacing.md, plus agent-building-guidelines/multi-agent-economics.md
Degraded environments (no git, missing tools)	skill-building-guidance/graceful-degradation.md, skill-building-guidance/optional-git-repositories.md
Frontmatter safety (angle brackets, YAML types)	skill-building-guidance/security-restrictions.md
Hardening fuzzy steps into deterministic ones	skill-building-guidance/hardening-fuzzy-vs-deterministic.md
Splitting or composing skills	skill-building-guidance/skill-decomposition.md, skill-building-guidance/skill-composition.md
Defining success and tests	skill-building-guidance/success-criteria-and-testing.md
New plugin needed (plugin.json, marketplace.json)	claude-marketplace-and-plugin-configuration/ and templates/

Operating Principles

• Interview relentlessly, but explore first. Interview the user relentlessly about every aspect of the skill until you reach a shared understanding. Walk down each branch of the design tree, resolving dependencies between decisions one-by-one. If a question can be answered by exploring the repository — the target plugin's existing skills, sibling descriptions, plugin.json, conventions, the guidance documents above — explore instead of asking. Only surface questions that genuinely require the user's judgment.
• Ask one question at a time. Never batch questions. Settle one decision, let its answer resolve dependent decisions, then ask the next. Later answers routinely make earlier questions moot.
• Recommend, then ask. For every question surfaced to the user, provide a recommended answer with rationale grounded in evidence (existing skills, conventions, the guidance, the user's stated goal). The user can accept, amend, or redirect.
• Apply guidance as you go, then verify at the end. Consult the governing document when a decision is on the table (Step 4), and run a full guidance-conformance pass over the finished files at the end (Step 6). The interview gets each decision approximately right; the review pass makes the artifact correct.

Build a Skill

Step 1: Capture the Request and Confirm It Is a Skill

Read the user's argument and the conversation to extract what the skill should do. If the request is too thin to start (for example, just "build a skill"), ask the user for one or two sentences on what the skill should accomplish and what triggers it — nothing else yet.

Confirm the entity type before anything else. Read ${CLAUDE_PLUGIN_ROOT}/skills/guidance/references/plugin-entity-taxonomy.md and apply its decision heuristic. A skill is a deterministic, flowchartable process ("Can I flowchart every path?" → skill). If the work is really contextual judgment with no fixed flowchart, it is an agent — stop and recommend agent-builder. If it fires automatically on an event, it is a hook. If the request bundles a deterministic process and a judgment layer, recommend building them separately and composing them. Only proceed once a skill is the right entity.

Step 2: Discover Before Asking

Locate the target plugin and learn its conventions before asking the user anything beyond the framing. Use Glob, Grep, and find to gather:

• The target plugin directory and its .claude-plugin/plugin.json (name, description, version). If the user has not said which plugin, infer candidates from the repository and confirm the target in Step 4.
• Sibling skills in that plugin ({plugin}/skills/*/SKILL.md) — their descriptions, frontmatter, step structure, and the trigger space they already own. New descriptions must disambiguate against these siblings in both directions.
• CLAUDE.md, AGENTS.md, and any project-discovery.md — repository conventions, the documentation root, and how skills are catalogued.
• Whether the skill needs an external tool (gh, jq, an MCP server). External dependencies drive the directory-name prefix and a description mention.

Record what was found (file paths) and what was not. A missing convention is itself a finding that shapes the skill.

Step 3: Build the Design Tree

Enumerate the decisions the skill needs, in dependency order. Resolve foundational decisions before dependent ones; never ask a dependent question before its parent is settled.

1. Foundational — Which plugin owns it? What are the 2-3 concrete use cases (trigger phrase, workflow, tools, domain knowledge) per use-case-planning.md? What artifact or outcome does each use case produce?
2. Identity — What is the directory name (which becomes the slash command)? Does it follow the gerund/process-name and dependency-prefix rules? What does the description say across all four components (what, when, boundary, breadth), and how does it disambiguate against siblings in both directions?
3. Workflow — Which workflow pattern fits (sequential, iterative, context-aware, domain-specific, or a combination)? What are the numbered steps? Where do human gates belong (before irreversible or outward-facing actions only)?
4. Capabilities — What allowed-tools does each step need, at the right Bash granularity? Does the skill dispatch agents (and are they available in this plugin)? Does it run scripts? Does it read runtime config via context injection?
5. Layout — What belongs in the SKILL.md body (process), in references/ (templates, checklists, domain knowledge), in scripts/ (deterministic operations), and in assets/ (output files)? What other frontmatter fields apply (argument-hint, arguments, model, paths)?

Keep each node a concrete decision with a candidate answer. Do not pre-fill the tree with content the user has not confirmed.

Step 4: Interview Loop — One Branch at a Time

For each decision in dependency order:

1. Try to resolve it from evidence. Re-check the target plugin, sibling skills, conventions, and the governing guidance document for this decision (see the map above). If the evidence answers it, record the decision with its evidence and move on — do not ask.
2. If evidence is insufficient, draft a recommended answer grounded in the guidance and the evidence available. Read the governing document first so the recommendation is correct, not improvised.
3. Surface one question to the user, with the recommendation, the rationale, and the alternatives. State what changes depending on the answer. Wait for the answer before asking anything else.
4. Descend. Once a decision is settled, re-evaluate which dependent decisions the new answer resolves, and continue.

Keep the interview moving — do not stall on questions the evidence can answer, and do not batch.

Step 5: Write the Skill

Create the skill directory and write the files:

1. Create {plugin}/skills/{skill-name}/ (use mkdir). The directory name is the slash command and must match the frontmatter name.
2. Write SKILL.md with:
   • Frontmatter: name (matching the directory), the description settled in the interview, allowed-tools, and any other settled fields. Never put AskUserQuestion in allowed-tools. No XML angle brackets in any frontmatter value.
   • A body of numbered process steps following the chosen workflow pattern. Be specific and actionable, embed reasoning in constraints (Always/Never X BECAUSE Y), include error handling for tool-dependent steps, and reference any bundled resource by exact path.
3. Create references/, scripts/, or assets/ and their files only if a use case needs them. Domain knowledge (templates, checklists, matrices) goes in references/; deterministic operations go in scripts/; output-only files go in assets/. Do not create empty or speculative folders.
4. If the skill belongs in a brand-new plugin, create the plugin scaffold (.claude-plugin/plugin.json, and a marketplace entry if the repo uses one) per the claude-marketplace-and-plugin-configuration/ guidance and the templates/.

Step 6: Full Guidance-Conformance Review

This is the review pass the skill commits to. Re-read each governing document that applies to what you built and verify the finished files against it, applying every fix directly. Do not summarize problems for the user without fixing them. Cover at minimum:

1. Entity fit (plugin-entity-taxonomy.md) — the skill is genuinely a flowchartable process, not a judgment layer that should be an agent.
2. Description (skill-description-frontmatter.md, skill-description-length.md) — third person; covers what, when, boundary, and trigger breadth; weaves trigger words into prose rather than appending a keyword list; names sibling skills in boundary clauses; disambiguates in both directions (update the sibling's description if a one-way gap exists); within 1024 characters.
3. Naming (naming-conventions.md) — directory name matches name, is a process/gerund name when the output is a plan or doc, carries a dependency prefix when an external tool is required, no README.md in the skill folder, SKILL.md cased exactly.
4. Progressive disclosure (progressive-disclosure.md, skill-reference-files.md) — body is process only and under 500 lines; domain knowledge is in references/; scripts hold deterministic work; nothing the toolchain already enforces is restated.
5. Instruction quality (writing-effective-instructions.md, workflow-patterns.md) — steps are specific and actionable; constraints embed reasoning; error handling is present; human gates sit only at irreversible actions; the most critical item in each list is placed last.
6. Tools and safety (allowed-tools-bash-permissions.md, allowed-tools-AskUserQuestion.md, security-restrictions.md) — Bash permissions are scoped correctly with separate entries; AskUserQuestion is absent from allowed-tools; no angle brackets or non-standard YAML in frontmatter.
7. Discovery and degradation (dynamic-project-discovery.md, graceful-degradation.md, optional-git-repositories.md) — the skill discovers project specifics dynamically rather than hardcoding them, and degrades gracefully when a tool or git is absent, where relevant.
8. Dispatch (agent-dispatch-namespacing.md) — if the skill dispatches agents, every dispatch uses the qualified defining-plugin:agent-name, and the agents actually exist in an installed plugin.
9. Tests (success-criteria-and-testing.md) — each use case maps to a triggering and functional test the user can run.

Apply the YAGNI discipline throughout: every step, reference file, tool permission, and frontmatter field must earn its place against a real use case. Cut anything added "for completeness" or "for future flexibility."

Step 7: Present and Hand Off

Summarize for the user:

• The files written (paths), and what each contains.
• The decisions settled by evidence versus by user input.
• The fixes the Step 6 review applied, citing the guidance document behind each.
• The triggering and functional tests derived from the use cases, so the user can validate the skill against the model tier it targets.

Note that plugin entities rarely land in one pass: per iterative-plugin-development.md, plan for 3-5 iterations. Ask whether the user wants to iterate on specific steps or considers the skill ready to test.