diff --git a/scripts/config_validator.py b/scripts/config_validator.py
new file mode 100644
index 00000000..d5b6b9d4
--- /dev/null
+++ b/scripts/config_validator.py
@@ -0,0 +1,306 @@
+#!/usr/bin/env python3
+"""
+config_validator.py — Validate all YAML/JSON config files in timmy-config.
+
+Checks:
+  1. YAML syntax (pyyaml safe_load)
+  2. JSON syntax (json.loads)
+  3. Duplicate keys in YAML/JSON
+  4. Trailing whitespace in YAML
+  5. Tabs in YAML (should use spaces)
+  6. Cron expression validity (if present)
+
+Exit 0 if all valid, 1 if any invalid.
+"""
+
+import json
+import os
+import re
+import sys
+from pathlib import Path
+
+try:
+    import yaml
+except ImportError:
+    print("ERROR: PyYAML not installed. Run: pip install pyyaml")
+    sys.exit(1)
+
+
+# ── Cron validation ──────────────────────────────────────────────────────────
+
+DOW_NAMES = {"sun", "mon", "tue", "wed", "thu", "fri", "sat"}
+MONTH_NAMES = {"jan", "feb", "mar", "apr", "may", "jun",
+               "jul", "aug", "sep", "oct", "nov", "dec"}
+
+
+def _expand_cron_field(field: str, lo: int, hi: int, names: dict | None = None) -> set[int]:
+    """Expand a single cron field into a set of valid integers."""
+    result: set[int] = set()
+    for part in field.split(","):
+        # Handle step: */N or 1-5/N
+        step = 1
+        if "/" in part:
+            part, step_str = part.split("/", 1)
+            if not step_str.isdigit() or int(step_str) < 1:
+                raise ValueError(f"invalid step value: {step_str}")
+            step = int(step_str)
+
+        if part == "*":
+            rng = range(lo, hi + 1, step)
+        elif "-" in part:
+            a, b = part.split("-", 1)
+            a = _resolve_name(a, names, lo, hi)
+            b = _resolve_name(b, names, lo, hi)
+            if a > b:
+                raise ValueError(f"range {a}-{b} is reversed")
+            rng = range(a, b + 1, step)
+        else:
+            val = _resolve_name(part, names, lo, hi)
+            rng = range(val, val + 1)
+
+        for v in rng:
+            if v < lo or v > hi:
+                raise ValueError(f"value {v} out of range [{lo}-{hi}]")
+            result.add(v)
+    return result
+
+
+def _resolve_name(token: str, names: dict | None, lo: int, hi: int) -> int:
+    if names and token.lower() in names:
+        return names[token.lower()]
+    if not token.isdigit():
+        raise ValueError(f"unrecognized token: {token}")
+    val = int(token)
+    if val < lo or val > hi:
+        raise ValueError(f"value {val} out of range [{lo}-{hi}]")
+    return val
+
+
+def validate_cron(expr: str) -> list[str]:
+    """Validate a 5-field cron expression. Returns list of errors (empty = ok)."""
+    errors: list[str] = []
+    fields = expr.strip().split()
+    if len(fields) != 5:
+        return [f"expected 5 fields, got {len(fields)}"]
+
+    specs = [
+        (fields[0], 0, 59, None, "minute"),
+        (fields[1], 0, 23, None, "hour"),
+        (fields[2], 1, 31, None, "day-of-month"),
+        (fields[3], 1, 12, MONTH_NAMES, "month"),
+        (fields[4], 0, 7, DOW_NAMES, "day-of-week"),
+    ]
+    for field, lo, hi, names, label in specs:
+        try:
+            _expand_cron_field(field, lo, hi, names)
+        except ValueError as e:
+            errors.append(f"{label}: {e}")
+    return errors
+
+
+# ── Duplicate key detection ──────────────────────────────────────────────────
+
+class DuplicateKeyError(Exception):
+    pass
+
+
+class _StrictYAMLLoader(yaml.SafeLoader):
+    """YAML loader that rejects duplicate keys."""
+    pass
+
+
+def _no_duplicates_constructor(loader, node, deep=False):
+    mapping = {}
+    for key_node, value_node in node.value:
+        key = loader.construct_object(key_node, deep=deep)
+        if key in mapping:
+            raise DuplicateKeyError(
+                f"duplicate key '{key}' (line {key_node.start_mark.line + 1})"
+            )
+        mapping[key] = loader.construct_object(value_node, deep=deep)
+    return mapping
+
+
+_StrictYAMLLoader.add_constructor(
+    yaml.resolver.BaseResolver.DEFAULT_MAPPING_TAG,
+    _no_duplicates_constructor,
+)
+
+
+def _json_has_duplicates(text: str) -> list[str]:
+    """Check for duplicate keys in JSON by scanning for repeated quoted keys at same depth."""
+    errors: list[str] = []
+    # Use a custom approach: parse with object_pairs_hook
+    seen_stack: list[set[str]] = []
+
+    def _check_pairs(pairs):
+        level_keys: set[str] = set()
+        for k, _ in pairs:
+            if k in level_keys:
+                errors.append(f"duplicate JSON key: '{k}'")
+            level_keys.add(k)
+        return dict(pairs)
+
+    try:
+        json.loads(text, object_pairs_hook=_check_pairs)
+    except json.JSONDecodeError:
+        pass  # syntax errors caught elsewhere
+    return errors
+
+
+# ── Main validator ───────────────────────────────────────────────────────────
+
+def find_config_files(root: Path) -> list[Path]:
+    """Recursively find .yaml, .yml, .json files (skip .git, node_modules, venv)."""
+    skip_dirs = {".git", "node_modules", "venv", "__pycache__", ".venv"}
+    results: list[Path] = []
+    for dirpath, dirnames, filenames in os.walk(root):
+        dirnames[:] = [d for d in dirnames if d not in skip_dirs]
+        for fname in filenames:
+            if fname.endswith((".yaml", ".yml", ".json")):
+                results.append(Path(dirpath) / fname)
+    return sorted(results)
+
+
+def validate_yaml_file(filepath: Path, text: str) -> list[str]:
+    """Validate a YAML file. Returns list of errors."""
+    errors: list[str] = []
+
+    # Check for tabs
+    for i, line in enumerate(text.splitlines(), 1):
+        if "\t" in line:
+            errors.append(f"  line {i}: contains tab character (use spaces for YAML)")
+        if line != line.rstrip():
+            errors.append(f"  line {i}: trailing whitespace")
+
+    # Check syntax + duplicate keys
+    try:
+        yaml.load(text, Loader=_StrictYAMLLoader)
+    except DuplicateKeyError as e:
+        errors.append(f"  {e}")
+    except yaml.YAMLError as e:
+        mark = getattr(e, "problem_mark", None)
+        if mark:
+            errors.append(f"  YAML syntax error at line {mark.line + 1}, col {mark.column + 1}: {e.problem}")
+        else:
+            errors.append(f"  YAML syntax error: {e}")
+
+    # Check cron expressions in schedule fields
+    for i, line in enumerate(text.splitlines(), 1):
+        cron_match = re.search(r'(?:cron|schedule)\s*:\s*["\']?([*0-9/,a-zA-Z-]+(?:\s+[*0-9/,a-zA-Z-]+){4})["\']?', line)
+        if cron_match:
+            cron_errs = validate_cron(cron_match.group(1))
+            for ce in cron_errs:
+                errors.append(f"  line {i}: invalid cron '{cron_match.group(1)}': {ce}")
+
+    return errors
+
+
+def validate_json_file(filepath: Path, text: str) -> list[str]:
+    """Validate a JSON file. Returns list of errors."""
+    errors: list[str] = []
+
+    # Check syntax
+    try:
+        json.loads(text)
+    except json.JSONDecodeError as e:
+        errors.append(f"  JSON syntax error at line {e.lineno}, col {e.colno}: {e.msg}")
+
+    # Check duplicate keys
+    dup_errors = _json_has_duplicates(text)
+    errors.extend(dup_errors)
+
+    # Check for trailing whitespace (informational)
+    for i, line in enumerate(text.splitlines(), 1):
+        if line != line.rstrip():
+            errors.append(f"  line {i}: trailing whitespace")
+
+    # Check cron expressions
+    cron_pattern = re.compile(r'"(?:cron|schedule)"?\s*:\s*"([^"]{5,})"')
+    for match in cron_pattern.finditer(text):
+        candidate = match.group(1).strip()
+        fields = candidate.split()
+        if len(fields) == 5 and all(re.match(r'^[*0-9/,a-zA-Z-]+$', f) for f in fields):
+            cron_errs = validate_cron(candidate)
+            for ce in cron_errs:
+                errors.append(f"  invalid cron '{candidate}': {ce}")
+
+    # Also check nested schedule objects with cron fields
+    try:
+        obj = json.loads(text)
+        _scan_obj_for_cron(obj, errors)
+    except Exception:
+        pass
+
+    return errors
+
+
+def _scan_obj_for_cron(obj, errors: list[str], path: str = ""):
+    """Recursively scan dict/list for cron expressions."""
+    if isinstance(obj, dict):
+        for k, v in obj.items():
+            if k in ("cron", "schedule", "cron_expression") and isinstance(v, str):
+                fields = v.strip().split()
+                if len(fields) == 5:
+                    cron_errs = validate_cron(v)
+                    for ce in cron_errs:
+                        errors.append(f"  {path}.{k}: invalid cron '{v}': {ce}")
+            _scan_obj_for_cron(v, errors, f"{path}.{k}")
+    elif isinstance(obj, list):
+        for i, item in enumerate(obj):
+            _scan_obj_for_cron(item, errors, f"{path}[{i}]")
+
+
+def main():
+    # Determine repo root (script lives in scripts/)
+    script_path = Path(__file__).resolve()
+    repo_root = script_path.parent.parent
+
+    print(f"Config Validator — scanning {repo_root}")
+    print("=" * 60)
+
+    files = find_config_files(repo_root)
+    print(f"Found {len(files)} config files to validate.\n")
+
+    total_errors = 0
+    failed_files: list[tuple[Path, list[str]]] = []
+
+    for filepath in files:
+        rel = filepath.relative_to(repo_root)
+        try:
+            text = filepath.read_text(encoding="utf-8", errors="replace")
+        except Exception as e:
+            failed_files.append((rel, [f"  cannot read file: {e}"]))
+            total_errors += 1
+            continue
+
+        if filepath.suffix == ".json":
+            errors = validate_json_file(filepath, text)
+        else:
+            errors = validate_yaml_file(filepath, text)
+
+        if errors:
+            failed_files.append((rel, errors))
+            total_errors += len(errors)
+            print(f"FAIL  {rel}")
+        else:
+            print(f"PASS  {rel}")
+
+    print("\n" + "=" * 60)
+    print(f"Results: {len(files) - len(failed_files)}/{len(files)} files passed")
+
+    if failed_files:
+        print(f"\n{total_errors} error(s) in {len(failed_files)} file(s):\n")
+        for relpath, errs in failed_files:
+            print(f"  {relpath}:")
+            for e in errs:
+                print(f"    {e}")
+        print()
+        sys.exit(1)
+    else:
+        print("\nAll config files valid!")
+        sys.exit(0)
+
+
+if __name__ == "__main__":
+    main()