diff --git a/tools/README.md b/tools/README.md
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+++ b/tools/README.md
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+# Skill Validation Tools
+
+## validate-skill.py
+
+Validate SKILL.md metadata before submitting a PR.
+
+### Usage
+
+```bash
+# Validate a single skill
+python tools/validate-skill.py skills/my-new-skill/
+
+# Validate all skills
+python tools/validate-skill.py --all
+```
+
+### What it checks
+
+- SKILL.md exists in the skill directory
+- Valid YAML frontmatter (between `---` markers)
+- Required fields present: `name`, `description`, `domain`, `subdomain`, `tags`
+- Name is kebab-case, 1–64 characters
+- Description is at least 50 characters (no upper limit; multi-line folded scalars are valid)
+- Domain is `cybersecurity`
+- Subdomain is from the allowed list
+- Tags is a list with at least 2 items
+
+### Requirements
+
+Python 3.8+ (stdlib only, no external dependencies)
diff --git a/tools/validate-skill.py b/tools/validate-skill.py
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+++ b/tools/validate-skill.py
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+#!/usr/bin/env python3
+"""Validate SKILL.md metadata for the Anthropic-Cybersecurity-Skills repository.
+
+Usage:
+    python tools/validate-skill.py skills/my-skill/
+    python tools/validate-skill.py --all
+"""
+import os
+import re
+import sys
+import glob
+
+REQUIRED_FIELDS = ["name", "description", "domain", "subdomain", "tags"]
+
+# Canonical subdomain → set of accepted aliases (including canonical itself).
+# When a skill uses an alias, the validator accepts it but the canonical form
+# is the first entry in each group below.  New skills should use the canonical.
+_SUBDOMAIN_ALIASES = {
+    # identity
+    "identity-access-management": {"identity-access-management", "identity-and-access-management", "identity-security"},
+    # zero-trust
+    "zero-trust-architecture": {"zero-trust-architecture", "zero-trust"},
+    # OT/ICS
+    "ot-ics-security": {"ot-ics-security", "ot-security"},
+    # SOC / security ops
+    "soc-operations": {"soc-operations", "security-operations"},
+    # red team
+    "red-teaming": {"red-teaming", "red-team"},
+    # standalone (no aliases)
+    "web-application-security": {"web-application-security", "application-security"},
+    "network-security": {"network-security"},
+    "penetration-testing": {"penetration-testing", "offensive-security"},
+    "digital-forensics": {"digital-forensics"},
+    "malware-analysis": {"malware-analysis"},
+    "threat-intelligence": {"threat-intelligence"},
+    "cloud-security": {"cloud-security"},
+    "container-security": {"container-security"},
+    "cryptography": {"cryptography"},
+    "vulnerability-management": {"vulnerability-management"},
+    "compliance-governance": {"compliance-governance", "governance-risk-compliance"},
+    "devsecops": {"devsecops"},
+    "threat-hunting": {"threat-hunting"},
+    "incident-response": {"incident-response"},
+    "endpoint-security": {"endpoint-security"},
+    "phishing-defense": {"phishing-defense", "social-engineering-defense"},
+    "api-security": {"api-security"},
+    "mobile-security": {"mobile-security"},
+    "ransomware-defense": {"ransomware-defense"},
+    "threat-detection": {"threat-detection"},
+    "blockchain-security": {"blockchain-security"},
+    "data-protection": {"data-protection"},
+    "deception-technology": {"deception-technology"},
+    "firmware-analysis": {"firmware-analysis", "firmware-security"},
+    "privacy-compliance": {"privacy-compliance"},
+    "purple-team": {"purple-team"},
+    "supply-chain-security": {"supply-chain-security"},
+    "wireless-security": {"wireless-security"},
+    "ai-security": {"ai-security"},
+}
+
+# Flat set of all accepted subdomain values (canonical + aliases).
+ALLOWED_SUBDOMAINS: set = {v for group in _SUBDOMAIN_ALIASES.values() for v in group}
+
+# Reverse map: alias → canonical (for warning messages).
+_ALIAS_TO_CANONICAL: dict = {}
+for canonical, aliases in _SUBDOMAIN_ALIASES.items():
+    for alias in aliases:
+        _ALIAS_TO_CANONICAL[alias] = canonical
+
+KEBAB_RE = re.compile(r"^[a-z0-9]+(-[a-z0-9]+)*$")
+
+# Minimum description length.  Other repo tooling uses 50 chars; align here.
+DESCRIPTION_MIN_CHARS = 50
+
+RED = "\033[91m"
+GREEN = "\033[92m"
+YELLOW = "\033[93m"
+RESET = "\033[0m"
+
+
+def parse_frontmatter(text):
+    """Extract YAML frontmatter as a dict (simple stdlib-only parser).
+
+    Handles the common SKILL.md patterns:
+    - key: scalar value
+    - key: [inline, list]
+    - key:\n  - list\n  - items
+    - key: >-  (folded scalar — content on following indented lines)
+
+    Edge case note: ``list_values`` is reset to ``[]`` whenever a new key
+    with a scalar value is encountered, so a list from a prior block cannot
+    leak into an unrelated key.  The only remaining theoretical edge case is
+    a key with *no* value that is immediately followed by non-list, non-empty
+    lines that look like scalars — those lines are currently ignored (the key
+    is treated as having no value).  This is acceptable for well-formed SKILL.md
+    files and matches the behaviour contributors expect.
+    """
+    if not text.startswith("---"):
+        return None
+    end = text.find("---", 3)
+    if end == -1:
+        return None
+    block = text[3:end].strip()
+    data = {}
+    current_key = None
+    list_values: list = []
+    in_folded = False  # True when we are collecting a YAML >- / > folded scalar
+    folded_lines: list = []
+
+    for line in block.split("\n"):
+        stripped = line.strip()
+
+        # Flush a completed folded scalar when we hit the next top-level key.
+        if in_folded and stripped and not line.startswith(" ") and not line.startswith("\t"):
+            if current_key and folded_lines:
+                data[current_key] = " ".join(folded_lines)
+            in_folded = False
+            folded_lines = []
+            current_key = None
+
+        if in_folded:
+            if stripped:
+                folded_lines.append(stripped)
+            continue
+
+        if not stripped or stripped.startswith("#"):
+            continue
+
+        # Handle list items (must come before key: value to avoid misparse).
+        if stripped.startswith("- ") and current_key:
+            list_values.append(stripped[2:].strip().strip('"').strip("'"))
+            data[current_key] = list(list_values)  # copy so future mutations don't leak
+            continue
+
+        # Handle inline list: tags: [a, b, c]
+        m = re.match(r"^(\w[\w_-]*):\s*\[(.+)\]\s*$", stripped)
+        if m:
+            current_key = m.group(1)
+            items = [i.strip().strip('"').strip("'") for i in m.group(2).split(",")]
+            data[current_key] = items
+            list_values = list(items)
+            continue
+
+        # Handle key: >- or key: > (folded scalar start)
+        m = re.match(r"^(\w[\w_-]*):\s*>[-|]?\s*$", stripped)
+        if m:
+            current_key = m.group(1)
+            list_values = []
+            in_folded = True
+            folded_lines = []
+            continue
+
+        # Handle key: value (plain scalar)
+        m = re.match(r'^(\w[\w_-]*):\s*(.*)$', stripped)
+        if m:
+            current_key = m.group(1)
+            val = m.group(2).strip().strip('"').strip("'")
+            list_values = []  # reset; new scalar key cannot inherit a prior list
+            if val:
+                data[current_key] = val
+            # If val is empty the key is present but value-less (e.g. start of block list)
+            continue
+
+    # Flush any trailing folded scalar.
+    if in_folded and current_key and folded_lines:
+        data[current_key] = " ".join(folded_lines)
+
+    return data
+
+
+def validate_skill(skill_dir):
+    """Validate a single skill directory. Returns list of error strings."""
+    errors = []
+    skill_md = os.path.join(skill_dir, "SKILL.md")
+
+    if not os.path.isfile(skill_md):
+        return [f"SKILL.md not found in {skill_dir}"]
+
+    try:
+        with open(skill_md, encoding="utf-8") as f:
+            content = f.read()
+    except IOError as e:
+        return [f"Could not read SKILL.md: {e}"]
+    except UnicodeDecodeError as e:
+        return [f"Encoding error in SKILL.md (not valid UTF-8): {e}"]
+
+    fm = parse_frontmatter(content)
+    if fm is None:
+        return ["No valid YAML frontmatter found (must start with ---)"]
+
+    # Check required fields.
+    for field in REQUIRED_FIELDS:
+        if field not in fm:
+            errors.append(f"Missing required field: {field}")
+
+    # Validate name.
+    name = fm.get("name", "")
+    if name:
+        if not KEBAB_RE.match(name):
+            errors.append(
+                f"Name '{name}' is not valid kebab-case (lowercase letters, digits, hyphens only)"
+            )
+        if len(name) > 64:
+            errors.append(f"Name too long ({len(name)} chars, max 64)")
+
+    # Validate description.
+    desc = fm.get("description", "")
+    if isinstance(desc, list):
+        errors.append("Description must be a string value, not a list")
+    elif isinstance(desc, str):
+        if len(desc) < DESCRIPTION_MIN_CHARS:
+            errors.append(
+                f"Description too short ({len(desc)} chars, min {DESCRIPTION_MIN_CHARS})"
+            )
+        # No hard upper-limit enforced; multi-line folded scalars (>-) produce
+        # long strings that are valid and common in this repo.
+
+    # Validate domain.
+    domain = fm.get("domain", "")
+    if domain and domain != "cybersecurity":
+        errors.append(f"Domain must be 'cybersecurity', got '{domain}'")
+
+    # Validate subdomain.
+    subdomain = fm.get("subdomain", "")
+    if subdomain:
+        if subdomain not in ALLOWED_SUBDOMAINS:
+            errors.append(
+                f"Unknown subdomain '{subdomain}'. Allowed: {', '.join(sorted(ALLOWED_SUBDOMAINS))}"
+            )
+        else:
+            canonical = _ALIAS_TO_CANONICAL.get(subdomain, subdomain)
+            if subdomain != canonical:
+                # Warn (non-blocking) — alias is accepted but canonical is preferred
+                print(
+                    f"{YELLOW}WARN{RESET} subdomain '{subdomain}' is an alias;"
+                    f" canonical form is '{canonical}'"
+                )
+
+    # Validate tags.
+    tags = fm.get("tags", [])
+    if isinstance(tags, str):
+        tags = [tags]
+    if len(tags) < 2:
+        errors.append(f"Need at least 2 tags, got {len(tags)}")
+
+    return errors
+
+
+def main():
+    if len(sys.argv) < 2:
+        print(f"Usage: {sys.argv[0]} <skill-dir> | --all")
+        sys.exit(1)
+
+    if sys.argv[1] == "--all":
+        skill_dirs = sorted(glob.glob("skills/*/"))
+        if not skill_dirs:
+            print("ERROR: No skill directories found. Run from the repository root.")
+            sys.exit(1)
+    else:
+        skill_dirs = [sys.argv[1].rstrip("/") + "/"]
+
+    total = 0
+    passed = 0
+    failed = 0
+
+    for skill_dir in skill_dirs:
+        if not os.path.isdir(skill_dir.rstrip("/")):
+            print(f"{RED}SKIP{RESET} {skill_dir} — not a directory")
+            continue
+
+        total += 1
+        errors = validate_skill(skill_dir.rstrip("/"))
+
+        name = os.path.basename(skill_dir.rstrip("/"))
+        if errors:
+            failed += 1
+            print(f"{RED}FAIL{RESET} {name}")
+            for e in errors:
+                print(f"      {YELLOW}→ {e}{RESET}")
+        else:
+            passed += 1
+            print(f"{GREEN}PASS{RESET} {name}")
+
+    print(f"\n{'='*50}")
+    print(f"Total: {total}  {GREEN}Passed: {passed}{RESET}  {RED}Failed: {failed}{RESET}")
+
+    sys.exit(0 if failed == 0 else 1)
+
+
+if __name__ == "__main__":
+    main()