Skill Builder
Create Agent Skills with best practices, structure, validation, and testing. Use when designing or refining skills, prompts, references, or supporting files.
Install
$ agentstack add skill-existential-birds-beagle-skill-builder ✓ scanned · ✓ verified, works with Claude Code, Cursor, and more.
Security review
✓ PassedNo issues found. Passed automated security review. · v0.1.0 How review works →
- ✓ Prompt-injection patterns
- ✓ Secret / credential exfiltration
- ✓ Dangerous shell & filesystem operations
- ✓ Untrusted network calls
- ✓ Known-malicious package signatures
What it can access
- ✓ Network access No
- ✓ Filesystem access No
- ✓ Shell / process execution No
- ✓ Environment & secrets No
- ✓ Dynamic code execution No
From automated source analysis of v0.1.0. “Used” means the capability is present in the source — more access means more to trust, not that it’s unsafe.
Verified badge
Passed review? Show it. Paste this badge into your README, it links to the public security report.
Links to your public security report.[](https://agentstack.voostack.com/security/report/skill-existential-birds-beagle-skill-builder) Reliability & compatibility
Declared compatibility
Compatibility is declared by the source manifest. End-to-end runtime verification is coming, see below.
We're building live execution health for every listing: tool-call success rate, median latency, uptime, and last-checked timestamps, measured, not self-reported. It isn't live yet, so we don't show numbers we can't stand behind.
How agent discovery & health will work →About
Skill Builder
Create, validate, and refine Agent Skills.
Quick Start
- Gather the capability, triggers, and required domain knowledge.
- Choose a simple single-file skill or a multi-file skill with references.
- Write
SKILL.mdwith concise, trigger-focused instructions. - Add reference files only for detail that would otherwise bloat
SKILL.md. - Validate YAML frontmatter, file layout, and naming.
- 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.”
- Requirements — Pass: Capability, triggers, and any required domain knowledge (or explicit “none”) are written down or confirmed from the user.
- Structure — Pass: Single-file vs
SKILL.md+references/is chosen; heavy detail lives in references, not inlined inSKILL.md. - Draft — Pass: Frontmatter is valid YAML with
nameanddescription;SKILL.mdis ≤ 500 lines; every relative link fromSKILL.mdresolves to a path that exists under this skill directory; eachallowed-toolsentry (if present) is justified. - Trigger check — Pass: At least one natural-language user phrase plausibly matching the
descriptionis identified for a quick invocation test.
Validation
- Keep
SKILL.mdunder 500 lines. - Prefer one-level reference links.
- Avoid time-sensitive guidance.
- Confirm frontmatter is valid YAML.
- Check that any
allowed-toolsentries 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
- Source: existential-birds/beagle
- License: Apache-2.0
- Homepage: https://existentialbirds.com
Install and usage instructions live in the source repository linked above.
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Versions
- v0.1.0 Imported from the upstream source.