Authoring MateClaw Skills

Overview

A skill is a SKILL.md file — YAML frontmatter plus a markdown body of reusable instructions. There are two places a SKILL.md can live, and they have different creation paths:

1. Builtin (in-repo): mateclaw-server/src/main/resources/skills/<name>/SKILL.md — committed, shipped inside the server JAR. On every startup BuiltinSkillSeedService scans classpath*:skills/*/SKILL.md, parses each frontmatter, and upserts a row into mate_skill keyed by name. The SKILL.md is the single source of truth — no SQL seed entry is required.
2. Custom (runtime): created by an agent or user through the skill_manage tool. Stored as a mate_skill row with skill_type=custom and exported to the workspace at ~/.mateclaw/skills/<name>/. Not committed; lives per-installation.

This skill covers both. Note that skill_manage does NOT write into the in-repo skills/ tree — builtin skills are authored by writing the file directly and restarting.

When to Use

• You're adding a reusable workflow that should ship with MateClaw → builtin.
• You're editing an existing builtin skill under mateclaw-server/src/main/resources/skills/.
• An agent finished a complex task and wants to persist the approach → custom, via skill_manage.
• You're reviewing a SKILL.md for correct frontmatter and structure.

Don't use for: recording a one-off tip discovered while using a skill (that belongs in record_lesson / a per-skill LESSONS.md) or cross-skill memory notes (remember). This skill is about writing the skill document itself.

Required Frontmatter

The frontmatter is parsed by SkillFrontmatterParser: a regex (^---\s*\n(.*?)\n---\s*\n(.*)$) splits the fenced block, then SnakeYAML loads it as a mapping. Hard requirements:

• Starts with --- as the first bytes — no leading blank line, no BOM.
• A closing --- line follows, then the body. The body must be non-empty.
• The block between the fences parses as a YAML mapping.
• name is present — it is the upsert key. BuiltinSkillSeedService skips any SKILL.md with no name.
• description is present — a single line.

If the frontmatter regex fails to match, the parser treats the whole file as body with an empty name, and a builtin skill is silently skipped at seed time. A loadable skill ALWAYS has well-formed frontmatter.

Size & Naming Limits

• Skill content: ≤ 100,000 chars (MAX_CONTENT_CHARS, ~25k tokens) — enforced by skill_manage for custom skills. Builtin skills aren't hard-checked but should obey the same ceiling.
• Name: must match ^[a-z0-9][a-z0-9._-]{0,63}$ — lowercase letters and digits plus - _ ., starting with a letter or digit, ≤ 64 chars. skill_manage lowercases the name before validating.
• Description: keep it to one line. Peer skills run 40-70 chars — a tight trigger phrase, not a paragraph.
• Peer skills in resources/skills/ sit at 6-15k chars. Aim for that range; past ~20k, split detail into references/*.md.

Peer-Matched Frontmatter

Every shipped skill follows this shape:

---
name: my-skill-name
description: 'One line: what it does and when it fires.'
version: 1.0.0
tags:
- short
- descriptive
- tags
author: ported
---

Fields BuiltinSkillSeedService projects onto the mate_skill row:

version / author / tags are not validator-enforced, but every peer carries them — omitting makes the skill look half-finished. Use optional: true for heavyweight skills (paid CLI dependencies, external OAuth, niche integrations) so they ship dark and the user activates them deliberately.

Skill Structure

Shipped skills follow roughly:

# <Title>

## Overview          — one or two paragraphs: what and why.
## When to Use       — bulleted triggers, plus a "Don't use for:" counter-trigger.
## <Topic sections>  — quick-reference tables, exact commands, concrete recipes
                       (mvn test, paths under mateclaw-server/, etc.).
## Common Pitfalls   — numbered mistakes paired with their fixes.
## Verification Checklist — checkbox list of post-action checks.

Not every section is mandatory, but Overview + When to Use + an actionable body + Common Pitfalls is the minimum for the skill to read like a peer.

Directory Placement

mateclaw-server/src/main/resources/skills/<skill-name>/SKILL.md

The skills/ tree is flat — no category subdirectories. The seed glob classpath*:skills/*/SKILL.md matches exactly one level deep, so a skill nested under a category directory would never be scanned. The directory name SHOULD equal the frontmatter name. Supporting files go in references/ and scripts/ subdirectories (see below).

Builtin Workflow (in-repo)

1. Survey peers: ls mateclaw-server/src/main/resources/skills/ and read 2-3 SKILL.md files close to your topic — match tone and structure.
2. Create skills/<name>/SKILL.md with the file tools.
3. Validate that the frontmatter parses — see the checklist below.
4. Restart the server. BuiltinSkillSeedService seeds the new row only at startup; a running server will not see it. The service also skips re-seeding when no SKILL.md's size/mtime changed, so rebuilding the JAR is what makes a change land.
5. Commit the new skills/<name>/ directory. No SQL seed change is needed — the SKILL.md is the source of truth and obsoletes per-skill INSERT INTO mate_skill.

Custom Workflow (skill_manage)

Agents and users create runtime skills with the skill_manage tool — actions create | edit | patch | delete:

• create — a new skill from full SKILL.md content. Rejects a duplicate name.
• edit — a full-content rewrite of a custom skill.
• patch — find-and-replace one section (oldText → newText).
• delete — uninstall (logical delete plus workspace archive).

Notes:

• Every write is security-scanned (SkillSecurityService) before saving — dangerous patterns are rejected with the reason. Builtin SKILL.md files are NOT scanned; they are trusted committed source.
• edit / patch / delete refuse builtin skills ("cannot edit builtin skill"). To change a builtin skill, edit the resource file and restart.
• A custom skill is live immediately — the tool re-runs the resolver pipeline — so no restart is needed.

Supporting Files

Beyond SKILL.md, a skill directory may carry:

• references/*.md — long-form material the body links to. Use this to keep SKILL.md under ~20k chars.
• scripts/* — executable helpers a skill invokes.
• templates/, assets/ — used by some bundled skills (HTML templates, images, etc.).

SkillFileAccessPolicy only resolves runtime paths under references/ and scripts/, and rejects .. traversal or absolute paths — keep runtime-read files in those two directories.

Common Pitfalls

1. Leading whitespace before ---. The frontmatter regex anchors on ^---; a blank line or BOM makes the whole file parse as body with an empty name, and a builtin skill is silently skipped.
2. Expecting a running server to see a new builtin skill. BuiltinSkillSeedService seeds only at startup. Restart — or, for a quick iteration, create a custom skill via skill_manage, which is live immediately.
3. Trying to skill_manage edit a builtin skill. It is refused. Builtin skills are committed source — edit the file and restart.
4. Adding an INSERT INTO mate_skill for a new builtin skill. Unnecessary and discouraged — the SKILL.md is the source of truth and the seed service upserts by name.
5. Generic description. "Debug things" is weak. A peer description names the trigger — "4-phase root cause debugging: understand bugs before fixing." beats "Debug things."
6. Naming an external project or internal RFC in the skill body. Describe the function objectively. Shipped content states what it does, not where the idea came from — author: ported is the neutral attribution for an adapted skill.
7. Skill content over 100k chars. skill_manage rejects it outright; split detail into references/.
8. Mismatched directory and name. The upsert keys on the frontmatter name, but a directory that disagrees confuses everyone reading the tree. Keep them equal.

Verification Checklist

• File at mateclaw-server/src/main/resources/skills/<name>/SKILL.md (builtin); the directory name equals the frontmatter name
• Frontmatter starts at byte 0 with ---, closes with a --- line, and the body is non-empty
• name matches ^[a-z0-9][a-z0-9._-]{0,63}$; description is a single line
• version, tags, author present (peer-matched shape)
• Total file ≤ 100,000 chars (aim 6-15k; split into references/ past ~20k)
• Structure: # Title → ## Overview → ## When to Use → actionable body → ## Common Pitfalls → ## Verification Checklist
• No external project names or RFC numbers in the body
• Builtin: server restarted so BuiltinSkillSeedService seeds the row; the new skills/<name>/ directory is committed
• Custom: created via skill_manage, security scan reported PASSED