Add CI workflow to validate YAML frontmatter in PRs

Adds a GitHub Actions workflow that validates frontmatter in agent,
skill, and command .md files changed by a PR. Checks:

- Agents: name and description are present and parseable
- Skills: description is present (required for Skill tool discovery)
- Commands: description is present and parseable

The workflow only runs when PRs touch files in agents/, skills/, or
commands/ directories, and only validates the changed files.

.github/scripts/validate-frontmatter.ts

@@ -0,0 +1,273 @@
+#!/usr/bin/env bun
+/**
+ * Validates YAML frontmatter in agent, skill, and command .md files.
+ *
+ * Usage:
+ *   bun validate-frontmatter.ts                    # scan current directory
+ *   bun validate-frontmatter.ts /path/to/dir       # scan specific directory
+ *   bun validate-frontmatter.ts file1.md file2.md  # validate specific files
+ */
+
+import { parse as parseYaml } from "yaml";
+import { readdir, readFile } from "fs/promises";
+import { basename, join, relative, resolve } from "path";
+
+// Characters that require quoting in YAML values when unquoted:
+// {} [] flow indicators, * anchor/alias, & anchor, # comment,
+// ! tag, | > block scalars, % directive, @ ` reserved
+const YAML_SPECIAL_CHARS = /[{}[\]*&#!|>%@`]/;
+const FRONTMATTER_REGEX = /^---\s*\n([\s\S]*?)---\s*\n?/;
+
+/**
+ * Pre-process frontmatter text to quote values containing special YAML
+ * characters. This allows glob patterns like **\/*.{ts,tsx} to parse.
+ */
+function quoteSpecialValues(text: string): string {
+  const lines = text.split("\n");
+  const result: string[] = [];
+
+  for (const line of lines) {
+    const match = line.match(/^([a-zA-Z_-]+):\s+(.+)$/);
+    if (match) {
+      const [, key, value] = match;
+      if (!key || !value) {
+        result.push(line);
+        continue;
+      }
+      // Skip already-quoted values
+      if (
+        (value.startsWith('"') && value.endsWith('"')) ||
+        (value.startsWith("'") && value.endsWith("'"))
+      ) {
+        result.push(line);
+        continue;
+      }
+      if (YAML_SPECIAL_CHARS.test(value)) {
+        const escaped = value.replace(/\\/g, "\\\\").replace(/"/g, '\\"');
+        result.push(`${key}: "${escaped}"`);
+        continue;
+      }
+    }
+    result.push(line);
+  }
+
+  return result.join("\n");
+}
+
+interface ParseResult {
+  frontmatter: Record<string, unknown>;
+  content: string;
+  error?: string;
+}
+
+function parseFrontmatter(markdown: string): ParseResult {
+  const match = markdown.match(FRONTMATTER_REGEX);
+
+  if (!match) {
+    return {
+      frontmatter: {},
+      content: markdown,
+      error: "No frontmatter found",
+    };
+  }
+
+  const frontmatterText = quoteSpecialValues(match[1] || "");
+  const content = markdown.slice(match[0].length);
+
+  try {
+    const parsed = parseYaml(frontmatterText);
+    if (parsed && typeof parsed === "object" && !Array.isArray(parsed)) {
+      return { frontmatter: parsed as Record<string, unknown>, content };
+    }
+    return {
+      frontmatter: {},
+      content,
+      error: `YAML parsed but result is not an object (got ${typeof parsed}${Array.isArray(parsed) ? " array" : ""})`,
+    };
+  } catch (err) {
+    return {
+      frontmatter: {},
+      content,
+      error: `YAML parse failed: ${err instanceof Error ? err.message : err}`,
+    };
+  }
+}
+
+// --- Validation ---
+
+type FileType = "agent" | "skill" | "command";
+
+interface ValidationIssue {
+  level: "error" | "warning";
+  message: string;
+}
+
+function validateAgent(
+  frontmatter: Record<string, unknown>
+): ValidationIssue[] {
+  const issues: ValidationIssue[] = [];
+
+  if (!frontmatter["name"] || typeof frontmatter["name"] !== "string") {
+    issues.push({ level: "error", message: 'Missing required "name" field' });
+  }
+  if (
+    !frontmatter["description"] ||
+    typeof frontmatter["description"] !== "string"
+  ) {
+    issues.push({
+      level: "error",
+      message: 'Missing required "description" field',
+    });
+  }
+
+  return issues;
+}
+
+function validateSkill(
+  frontmatter: Record<string, unknown>
+): ValidationIssue[] {
+  const issues: ValidationIssue[] = [];
+
+  if (!frontmatter["description"] && !frontmatter["when_to_use"]) {
+    issues.push({
+      level: "error",
+      message: 'Missing required "description" field',
+    });
+  }
+
+  return issues;
+}
+
+function validateCommand(
+  frontmatter: Record<string, unknown>
+): ValidationIssue[] {
+  const issues: ValidationIssue[] = [];
+
+  if (
+    !frontmatter["description"] ||
+    typeof frontmatter["description"] !== "string"
+  ) {
+    issues.push({
+      level: "error",
+      message: 'Missing required "description" field',
+    });
+  }
+
+  return issues;
+}
+
+// --- File type detection ---
+
+function detectFileType(filePath: string): FileType | null {
+  if (filePath.includes("/agents/")) return "agent";
+  if (filePath.includes("/skills/") && basename(filePath) === "SKILL.md")
+    return "skill";
+  if (filePath.includes("/commands/")) return "command";
+  return null;
+}
+
+// --- File discovery ---
+
+async function findMdFiles(
+  baseDir: string
+): Promise<{ path: string; type: FileType }[]> {
+  const results: { path: string; type: FileType }[] = [];
+
+  async function walk(dir: string) {
+    const entries = await readdir(dir, { withFileTypes: true });
+    for (const entry of entries) {
+      const fullPath = join(dir, entry.name);
+      if (entry.isDirectory()) {
+        await walk(fullPath);
+      } else if (entry.name.endsWith(".md")) {
+        const type = detectFileType(fullPath);
+        if (type) {
+          results.push({ path: fullPath, type });
+        }
+      }
+    }
+  }
+
+  await walk(baseDir);
+  return results;
+}
+
+// --- Main ---
+
+async function main() {
+  const args = process.argv.slice(2);
+
+  let files: { path: string; type: FileType }[];
+  let baseDir: string;
+
+  if (args.length > 0 && args.every((a) => a.endsWith(".md"))) {
+    baseDir = process.cwd();
+    files = [];
+    for (const arg of args) {
+      const fullPath = resolve(arg);
+      const type = detectFileType(fullPath);
+      if (type) {
+        files.push({ path: fullPath, type });
+      }
+    }
+  } else {
+    baseDir = args[0] || process.cwd();
+    files = await findMdFiles(baseDir);
+  }
+
+  let totalErrors = 0;
+  let totalWarnings = 0;
+
+  console.log(`Validating ${files.length} frontmatter files...\n`);
+
+  for (const { path: filePath, type } of files) {
+    const rel = relative(baseDir, filePath);
+    const content = await readFile(filePath, "utf-8");
+    const result = parseFrontmatter(content);
+
+    const issues: ValidationIssue[] = [];
+
+    if (result.error) {
+      issues.push({ level: "error", message: result.error });
+    }
+
+    if (!result.error) {
+      switch (type) {
+        case "agent":
+          issues.push(...validateAgent(result.frontmatter));
+          break;
+        case "skill":
+          issues.push(...validateSkill(result.frontmatter));
+          break;
+        case "command":
+          issues.push(...validateCommand(result.frontmatter));
+          break;
+      }
+    }
+
+    if (issues.length > 0) {
+      console.log(`${rel} (${type})`);
+      for (const issue of issues) {
+        const prefix = issue.level === "error" ? "  ERROR" : "  WARN ";
+        console.log(`${prefix}: ${issue.message}`);
+        if (issue.level === "error") totalErrors++;
+        else totalWarnings++;
+      }
+      console.log();
+    }
+  }
+
+  console.log("---");
+  console.log(
+    `Validated ${files.length} files: ${totalErrors} errors, ${totalWarnings} warnings`
+  );
+
+  if (totalErrors > 0) {
+    process.exit(1);
+  }
+}
+
+main().catch((err) => {
+  console.error("Fatal error:", err);
+  process.exit(2);
+});

.github/workflows/validate-frontmatter.yml

@@ -0,0 +1,34 @@
+name: Validate Frontmatter
+
+on:
+  pull_request:
+    paths:
+      - '**/agents/*.md'
+      - '**/skills/*/SKILL.md'
+      - '**/commands/*.md'
+
+jobs:
+  validate:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: oven-sh/setup-bun@v2
+
+      - name: Install dependencies
+        run: cd .github/scripts && bun install yaml
+
+      - name: Get changed frontmatter files
+        id: changed
+        run: |
+          FILES=$(gh pr diff ${{ github.event.pull_request.number }} --name-only | grep -E '(agents/.*\.md|skills/.*/SKILL\.md|commands/.*\.md)$' || true)
+          echo "files<<EOF" >> "$GITHUB_OUTPUT"
+          echo "$FILES" >> "$GITHUB_OUTPUT"
+          echo "EOF" >> "$GITHUB_OUTPUT"
+        env:
+          GH_TOKEN: ${{ github.token }}
+
+      - name: Validate frontmatter
+        if: steps.changed.outputs.files != ''
+        run: |
+          echo "${{ steps.changed.outputs.files }}" | xargs bun .github/scripts/validate-frontmatter.ts

plugins/plugin-dev/agents/agent-creator.md

@@ -1,7 +1,6 @@
 ---
 name: agent-creator
-description: |
-  Use this agent when the user asks to "create an agent", "generate an agent", "build a new agent", "make me an agent that...", or describes agent functionality they need. Trigger when user wants to create autonomous agents for plugins. Examples:
+description: Use this agent when the user asks to "create an agent", "generate an agent", "build a new agent", "make me an agent that...", or describes agent functionality they need. Trigger when user wants to create autonomous agents for plugins. Examples:
 
 <example>
 Context: User wants to create a code review agent
@@ -29,6 +28,7 @@ description: |
 Plugin development with agent addition, trigger agent-creator.
 </commentary>
 </example>
+
 model: sonnet
 color: magenta
 tools: ["Write", "Read"]

plugins/plugin-dev/agents/plugin-validator.md

@@ -1,7 +1,6 @@
 ---
 name: plugin-validator
-description: |
-  Use this agent when the user asks to "validate my plugin", "check plugin structure", "verify plugin is correct", "validate plugin.json", "check plugin files", or mentions plugin validation. Also trigger proactively after user creates or modifies plugin components. Examples:
+description: Use this agent when the user asks to "validate my plugin", "check plugin structure", "verify plugin is correct", "validate plugin.json", "check plugin files", or mentions plugin validation. Also trigger proactively after user creates or modifies plugin components. Examples:
 
 <example>
 Context: User finished creating a new plugin
@@ -31,6 +30,7 @@ description: |
 </commentary>
 assistant: "I'll use the plugin-validator agent to check the manifest."
 </example>
+
 model: inherit
 color: yellow
 tools: ["Read", "Grep", "Glob", "Bash"]

plugins/plugin-dev/agents/skill-reviewer.md

@@ -1,7 +1,6 @@
 ---
 name: skill-reviewer
-description: |
-  Use this agent when the user has created or modified a skill and needs quality review, asks to "review my skill", "check skill quality", "improve skill description", or wants to ensure skill follows best practices. Trigger proactively after skill creation. Examples:
+description: Use this agent when the user has created or modified a skill and needs quality review, asks to "review my skill", "check skill quality", "improve skill description", or wants to ensure skill follows best practices. Trigger proactively after skill creation. Examples:
 
 <example>
 Context: User just created a new skill
@@ -30,6 +29,7 @@ description: |
 Skill description modified, review for triggering effectiveness.
 </commentary>
 </example>
+
 model: inherit
 color: cyan
 tools: ["Read", "Grep", "Glob"]

plugins/pr-review-toolkit/agents/code-simplifier.md

@@ -1,11 +1,6 @@
 ---
 name: code-simplifier
-description: |
-  Use this agent when code has been written or modified and needs to be simplified for clarity, consistency, and maintainability while preserving all functionality. This agent should be triggered automatically after completing a coding task or writing a logical chunk of code. It simplifies code by following project best practices while retaining all functionality. The agent focuses only on recently modified code unless instructed otherwise.
-
-  Examples:
-
-  <example>
+description: Use this agent when code has been written or modified and needs to be simplified for clarity, consistency, and maintainability while preserving all functionality. This agent should be triggered automatically after completing a coding task or writing a logical chunk of code. It simplifies code by following project best practices while retaining all functionality. The agent focuses only on recently modified code unless instructed otherwise.\n\nExamples:\n\n<example>
 Context: The assistant has just implemented a new feature that adds user authentication to an API endpoint.
 user: "Please add authentication to the /api/users endpoint"
 assistant: "I've implemented the authentication for the /api/users endpoint. Here's the code:"