Custom skills

You can add your own skills without a change to the server. This example was run on a clean home directory.

Where a skill goes

The user layer wins over the project layer. The project layer wins over the bundled skills. RULE_MCP_HOME moves the user directory.

Add a skill

Make the file ~/.rule-mcp/skills/my-rules/SKILL.md:

---
name: my-rules
description: House rules
exposeTool: true
guardrails: [myco-no-todo]
---

# my-rules

## Rules

- No TODO comments.

Make the file ~/.rule-mcp/skills/my-rules/guardrails/index.js:

export const noTodo = {
  id: "myco-no-todo",
  label: "No TODO comments",
  description: "Code must not hold TODO comments.",
  check: (code) => {
    const found = code.includes("TODO");

    return { pass: !found, failCount: found ? 1 : 0, detail: [], suggestion: "Remove the TODO." };
  },
};

Then do a check of the skill:

rule-mcp tools call rule_tool_check --json '{"code":"// TODO","skill":"my-rules"}'

The result includes myco-no-todo and the baseline rules.

Rules for a custom skill

• A custom skill makes a tool only if the frontmatter has exposeTool: true. Without it, search, check, and the gateway still read the skill.
• The guardrails list in the frontmatter must match the exports of guardrails/index.js. The server reports a difference by name.
• A skill with a name from the catalog replaces that skill.
• The server runs the code in guardrails/. Add only code that you trust.
• If a rule folder throws an error, the server reports it and continues.
• The rule://community resource lists the custom skills.

The file plugin.js has no effect. The server also does not read ~/.agents/skills/ as a skill layer.