# Skill Builder

> Create Agent Skills with best practices, structure, validation, and testing. Use when designing or refining skills, prompts, references, or supporting files.

- **Type:** Skill
- **Install:** `agentstack add skill-existential-birds-beagle-skill-builder`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [existential-birds](https://agentstack.voostack.com/s/existential-birds)
- **Installs:** 0
- **Category:** [AI & ML](https://agentstack.voostack.com/c/ai-and-ml)
- **Latest version:** 0.1.0
- **License:** Apache-2.0
- **Upstream author:** [existential-birds](https://github.com/existential-birds)
- **Source:** https://github.com/existential-birds/beagle/tree/main/plugins/beagle-core/skills/skill-builder
- **Website:** https://existentialbirds.com

## Install

```sh
agentstack add skill-existential-birds-beagle-skill-builder
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# Skill Builder

Create, validate, and refine Agent Skills.

## Quick Start

1. Gather the capability, triggers, and required domain knowledge.
2. Choose a simple single-file skill or a multi-file skill with references.
3. Write `SKILL.md` with concise, trigger-focused instructions.
4. Add reference files only for detail that would otherwise bloat `SKILL.md`.
5. Validate YAML frontmatter, file layout, and naming.
6. Test the skill with the natural language users are likely to say.

## Workflow

- Start with requirements and scope control.
- Design the structure before writing content.
- Keep descriptions in third person and include trigger keywords.
- Use progressive disclosure for long examples, templates, and validation details.

## Gates

Follow in order. **Pass** means a check you can satisfy with concrete artifacts (written bullets, paths, line counts, parsed YAML)—not an internal sense of “done.”

1. **Requirements** — **Pass:** Capability, triggers, and any required domain knowledge (or explicit “none”) are written down or confirmed from the user.
2. **Structure** — **Pass:** Single-file vs `SKILL.md` + `references/` is chosen; heavy detail lives in references, not inlined in `SKILL.md`.
3. **Draft** — **Pass:** Frontmatter is valid YAML with `name` and `description`; `SKILL.md` is ≤ 500 lines; every relative link from `SKILL.md` resolves to a path that exists under this skill directory; each `allowed-tools` entry (if present) is justified.
4. **Trigger check** — **Pass:** At least one natural-language user phrase plausibly matching the `description` is identified for a quick invocation test.

## Validation

- Keep `SKILL.md` under 500 lines.
- Prefer one-level reference links.
- Avoid time-sensitive guidance.
- Confirm frontmatter is valid YAML.
- Check that any `allowed-tools` entries are necessary and correct.

## Advanced Reference

For the full workflow, templates, examples, and validation checklist, see [references/skill-builder-guide.md](references/skill-builder-guide.md).

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [existential-birds](https://github.com/existential-birds)
- **Source:** [existential-birds/beagle](https://github.com/existential-birds/beagle)
- **License:** Apache-2.0
- **Homepage:** https://existentialbirds.com

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** no
- **Filesystem access:** no
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/skill-existential-birds-beagle-skill-builder
- Seller: https://agentstack.voostack.com/s/existential-birds
- Browse the marketplace: https://agentstack.voostack.com/browse

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Listed on AgentStack — the marketplace for AI agent skills and MCP servers. Every listing is security-reviewed. Creators keep 70%.