diff --git a/.github/workflows/skill-docs.yml b/.github/workflows/skill-docs.yml
index 700a8222a..ba4c6d0ab 100644
--- a/.github/workflows/skill-docs.yml
+++ b/.github/workflows/skill-docs.yml
@@ -31,3 +31,5 @@ jobs:
             echo "Generated Factory SKILL.md files are stale. Run: bun run gen:skill-docs --host factory"
             exit 1
           }
+      - name: Validate generated skill frontmatter
+        run: bun run skill:frontmatter
diff --git a/package.json b/package.json
index 5be9c32bc..1c7a42e79 100644
--- a/package.json
+++ b/package.json
@@ -31,6 +31,7 @@
     "test:gemini": "EVALS=1 bun test test/gemini-e2e.test.ts",
     "test:gemini:all": "EVALS=1 EVALS_ALL=1 bun test test/gemini-e2e.test.ts",
     "skill:check": "bun run scripts/skill-check.ts",
+    "skill:frontmatter": "bun run scripts/skill-frontmatter-check.ts",
     "dev:skill": "bun run scripts/dev-skill.ts",
     "start": "bun run browse/src/server.ts",
     "eval:list": "bun run scripts/eval-list.ts",
diff --git a/scripts/skill-check.ts b/scripts/skill-check.ts
index 9182737ee..878869531 100644
--- a/scripts/skill-check.ts
+++ b/scripts/skill-check.ts
@@ -8,7 +8,7 @@
  *   - Freshness check (generated files match committed files)
  */
 
-import { validateSkill } from '../test/helpers/skill-parser';
+import { validateSkill, validateSkillFrontmatter } from '../test/helpers/skill-parser';
 import { discoverTemplates, discoverSkillFiles } from './discover-skills';
 import * as fs from 'fs';
 import * as path from 'path';
@@ -35,6 +35,16 @@ let hasErrors = false;
 console.log('  Skills:');
 for (const file of SKILL_FILES) {
   const fullPath = path.join(ROOT, file);
+  const frontmatterErrors = validateSkillFrontmatter(fullPath);
+  if (frontmatterErrors.length > 0) {
+    hasErrors = true;
+    console.log(`  ❌ ${file.padEnd(30)} — invalid frontmatter`);
+    for (const err of frontmatterErrors) {
+      console.log(`      line ${err.line}: ${err.message}`);
+    }
+    continue;
+  }
+
   const result = validateSkill(fullPath);
 
   if (result.warnings.length > 0) {
diff --git a/scripts/skill-frontmatter-check.ts b/scripts/skill-frontmatter-check.ts
new file mode 100644
index 000000000..b82065cd5
--- /dev/null
+++ b/scripts/skill-frontmatter-check.ts
@@ -0,0 +1,54 @@
+#!/usr/bin/env bun
+/**
+ * Validate YAML frontmatter for generated SKILL.md files.
+ *
+ * This is intentionally narrower than skill:check so CI can run it after
+ * regenerating only the host outputs relevant to a workflow.
+ */
+
+import { discoverSkillFiles } from './discover-skills';
+import { validateSkillFrontmatter } from '../test/helpers/skill-parser';
+import * as fs from 'fs';
+import * as path from 'path';
+
+const ROOT = path.resolve(import.meta.dir, '..');
+
+function walkSkillFiles(dir: string, acc: string[]): void {
+  for (const entry of fs.readdirSync(dir, { withFileTypes: true })) {
+    if (entry.name === '.git' || entry.name === 'node_modules') continue;
+    const fullPath = path.join(dir, entry.name);
+    if (entry.isDirectory()) {
+      walkSkillFiles(fullPath, acc);
+      continue;
+    }
+    if (entry.name === 'SKILL.md') {
+      acc.push(path.relative(ROOT, fullPath));
+    }
+  }
+}
+
+const files = new Set(discoverSkillFiles(ROOT));
+for (const hostDir of ['.agents', '.factory']) {
+  const fullPath = path.join(ROOT, hostDir);
+  if (fs.existsSync(fullPath)) {
+    const hostFiles: string[] = [];
+    walkSkillFiles(fullPath, hostFiles);
+    for (const file of hostFiles) files.add(file);
+  }
+}
+
+const errors: string[] = [];
+for (const file of [...files].sort()) {
+  const fullPath = path.join(ROOT, file);
+  for (const error of validateSkillFrontmatter(fullPath)) {
+    errors.push(`${file}:${error.line}: ${error.message}`);
+  }
+}
+
+if (errors.length > 0) {
+  console.error('Invalid SKILL.md frontmatter:');
+  for (const error of errors) console.error(`  ${error}`);
+  process.exit(1);
+}
+
+console.log(`Validated frontmatter for ${files.size} SKILL.md files.`);
diff --git a/test/helpers/skill-parser.ts b/test/helpers/skill-parser.ts
index 0e3271ba1..d4152a6b6 100644
--- a/test/helpers/skill-parser.ts
+++ b/test/helpers/skill-parser.ts
@@ -34,6 +34,11 @@ export interface ValidationResult {
   warnings: string[];
 }
 
+export interface FrontmatterError {
+  line: number;
+  message: string;
+}
+
 /**
  * Extract all $B invocations from bash code blocks in a SKILL.md file.
  */
@@ -138,6 +143,50 @@ export function validateSkill(skillPath: string): ValidationResult {
   return result;
 }
 
+/**
+ * Lightweight frontmatter validation for the YAML subset used by SKILL.md.
+ *
+ * This intentionally does not try to be a complete YAML parser. It catches the
+ * class of errors that make agents skip skills: missing delimiters and plain
+ * scalar values that contain ": " without being quoted or written as a block.
+ */
+export function validateSkillFrontmatter(skillPath: string): FrontmatterError[] {
+  const content = fs.readFileSync(skillPath, 'utf-8');
+  const errors: FrontmatterError[] = [];
+
+  if (!content.startsWith('---\n')) {
+    return [{ line: 1, message: 'missing opening frontmatter delimiter' }];
+  }
+
+  const fmEnd = content.indexOf('\n---', 4);
+  if (fmEnd === -1) {
+    return [{ line: 1, message: 'missing closing frontmatter delimiter' }];
+  }
+
+  const frontmatter = content.slice(4, fmEnd);
+  const lines = frontmatter.split('\n');
+  for (let i = 0; i < lines.length; i++) {
+    const line = lines[i];
+    const match = line.match(/^\s*[A-Za-z0-9_-]+:\s+(.+?)\s*$/);
+    if (!match) continue;
+
+    const value = match[1].trim();
+    const isQuoted = value.startsWith('"') || value.startsWith("'");
+    const isBlockScalar = value === '|' || value === '>' || value.startsWith('|') || value.startsWith('>');
+    const isFlowValue = value.startsWith('[') || value.startsWith('{');
+    if (isQuoted || isBlockScalar || isFlowValue) continue;
+
+    if (/:\s/.test(value)) {
+      errors.push({
+        line: i + 2,
+        message: 'plain YAML scalar contains ": "; quote it or use a block scalar',
+      });
+    }
+  }
+
+  return errors;
+}
+
 /**
  * Extract all REMOTE_SLUG=$(...) assignment patterns from .md files in given subdirectories.
  * Returns a Map from filename → array of full assignment lines found.
diff --git a/test/skill-validation.test.ts b/test/skill-validation.test.ts
index df5cb7994..82b8385ce 100644
--- a/test/skill-validation.test.ts
+++ b/test/skill-validation.test.ts
@@ -1,5 +1,5 @@
 import { describe, test, expect } from 'bun:test';
-import { validateSkill, extractRemoteSlugPatterns, extractWeightsFromTable } from './helpers/skill-parser';
+import { validateSkill, validateSkillFrontmatter, extractRemoteSlugPatterns, extractWeightsFromTable } from './helpers/skill-parser';
 import { ALL_COMMANDS, COMMAND_DESCRIPTIONS, READ_COMMANDS, WRITE_COMMANDS, META_COMMANDS } from '../browse/src/commands';
 import { SNAPSHOT_FLAGS } from '../browse/src/snapshot';
 import * as fs from 'fs';
@@ -24,6 +24,30 @@ function readShipUnion(): string {
 }
 
 describe('SKILL.md command validation', () => {
+  test('all SKILL.md files have loadable YAML frontmatter', () => {
+    const skillFiles: string[] = [];
+    const walk = (dir: string) => {
+      for (const entry of fs.readdirSync(dir, { withFileTypes: true })) {
+        if (entry.name === 'node_modules' || entry.name === '.git') continue;
+        const fullPath = path.join(dir, entry.name);
+        if (entry.isDirectory()) {
+          walk(fullPath);
+        } else if (entry.name === 'SKILL.md') {
+          skillFiles.push(fullPath);
+        }
+      }
+    };
+    walk(ROOT);
+
+    const errors = skillFiles.flatMap((skillPath) =>
+      validateSkillFrontmatter(skillPath).map((error) =>
+        `${path.relative(ROOT, skillPath)}:${error.line}: ${error.message}`
+      )
+    );
+
+    expect(errors).toEqual([]);
+  });
+
   test('all $B commands in SKILL.md are valid browse commands', () => {
     const result = validateSkill(path.join(ROOT, 'SKILL.md'));
     expect(result.invalid).toHaveLength(0);