diff --git a/action.yml b/action.yml
index cf6382d..a2a5200 100644
--- a/action.yml
+++ b/action.yml
@@ -73,6 +73,14 @@ inputs:
     description: 'Path to a Markdown style configuration file (.md) containing documentation style guidelines. If not set, auto-detects .code-to-docs/style.md in the repository root.'
     required: false
     default: ''
+  mode:
+    description: 'Execution mode: "comment" (default), "detect-only", or "audit" (scheduled full-repo drift check)'
+    required: false
+    default: 'comment'
+  audit-budget:
+    description: 'Maximum number of doc files to audit per run (default: 20). Controls cost on large repos.'
+    required: false
+    default: '20'
 
 outputs:
   status:
@@ -104,3 +112,5 @@ runs:
     GOOGLE_SA_KEY: ${{ inputs.google-sa-key }}
     MAX_CONTEXT_CHARS: ${{ inputs.max-context-chars }}
     STYLE_CONFIG_PATH: ${{ inputs.style-config-path }}
+    MODE: ${{ inputs.mode }}
+    AUDIT_BUDGET: ${{ inputs.audit-budget }}
diff --git a/src/audit.py b/src/audit.py
new file mode 100644
index 0000000..e56a6da
--- /dev/null
+++ b/src/audit.py
@@ -0,0 +1,194 @@
+"""Scheduled full-repo documentation drift audit.
+
+Walks the docs tree using folder indexes, asks the LLM to assess each
+doc's staleness, and reports findings grouped by severity.
+"""
+
+import json
+import os
+
+from config import get_client, get_max_context_chars, get_model_name, truncate_content
+from doc_index import get_doc_folders, get_docs_in_folder, get_docs_root, load_manifest
+from security_utils import run_command_safe, sanitize_output
+
+
+def run_audit(max_files=20):
+    """Audit documentation for drift against the current codebase.
+
+    Returns a list of {file, severity, reason} dicts.
+    """
+    docs_root = get_docs_root().resolve()
+    findings = []
+    files_checked = 0
+    files_skipped = 0
+
+    folders = get_doc_folders(docs_root)
+    manifest = load_manifest(docs_root)
+
+    for folder in folders:
+        docs = get_docs_in_folder(folder, docs_root)
+        for doc in docs:
+            if files_checked >= max_files:
+                files_skipped += 1
+                continue
+
+            rel_path = str(doc.relative_to(docs_root))
+            try:
+                content = doc.read_text(encoding="utf-8")
+            except Exception:
+                continue
+
+            folder_info = manifest.get("folders", {}).get(folder, {})
+            index_summary = folder_info.get("index", "")
+
+            severity, reason = _assess_doc(rel_path, content, index_summary)
+            if severity != "fresh":
+                findings.append({"file": rel_path, "severity": severity, "reason": reason})
+            files_checked += 1
+
+    if files_skipped > 0:
+        print(
+            f"Audit budget reached: checked {files_checked} files, "
+            f"skipped {files_skipped}. Increase audit-budget to cover more."
+        )
+
+    return findings
+
+
+def _assess_doc(file_path, content, index_summary):
+    """Ask the LLM to assess a single doc's staleness.
+
+    Returns (severity, reason) where severity is "fresh", "stale", or "very-stale".
+    """
+    prompt = f"""Assess whether this documentation file is likely up to date with the current codebase.
+
+File: {file_path}
+
+Folder context: {index_summary[:500] if index_summary else "No index available"}
+
+Documentation content (first 2000 chars):
+{content[:2000]}
+
+Rate the doc as one of:
+- FRESH: content appears current, no obvious staleness
+- STALE: some sections may be outdated (e.g. refers to old defaults, missing recent features)
+- VERY-STALE: significant portions are likely incorrect or missing
+
+Respond with exactly one line: SEVERITY: brief reason
+Example: STALE: refers to v1 API but v2 has been released"""
+
+    budget = get_max_context_chars()
+    prompt = truncate_content(prompt, budget, label=f"audit prompt for {file_path}")
+
+    try:
+        client = get_client()
+        response = client.chat.completions.create(
+            model=get_model_name(),
+            messages=[{"role": "user", "content": prompt}],
+        )
+        text = (response.choices[0].message.content or "").strip()
+
+        for severity in ("VERY-STALE", "STALE", "FRESH"):
+            if severity in text.upper():
+                reason = text.split(":", 1)[1].strip() if ":" in text else text
+                return severity.lower(), reason
+
+        return "stale", text[:200]
+    except Exception as e:
+        print(f"Warning: Could not assess {file_path}: {sanitize_output(str(e))}")
+        return "fresh", ""
+
+
+def format_audit_report(findings):
+    """Format findings into a Markdown report grouped by severity."""
+    if not findings:
+        return "No documentation drift detected."
+
+    lines = ["# Documentation Drift Audit", ""]
+
+    for severity in ("very-stale", "stale"):
+        group = [f for f in findings if f["severity"] == severity]
+        if not group:
+            continue
+        label = "Very Stale" if severity == "very-stale" else "Stale"
+        lines.append(f"## {label} ({len(group)} file{'s' if len(group) != 1 else ''})")
+        lines.append("")
+        for f in group:
+            lines.append(f"- **{f['file']}**: {f['reason']}")
+        lines.append("")
+
+    return "\n".join(lines)
+
+
+def post_audit_issue(findings, repo=None):
+    """Create or update a single GitHub Issue with audit findings."""
+    gh_token = os.environ.get("GH_TOKEN")
+    if not gh_token:
+        print("Warning: GH_TOKEN not set, cannot post audit issue")
+        return
+
+    if repo is None:
+        repo = os.environ.get("GITHUB_REPOSITORY", "")
+    if not repo:
+        print("Warning: GITHUB_REPOSITORY not set, cannot post audit issue")
+        return
+
+    label = "docs-drift-audit"
+    title = "Documentation Drift Audit Report"
+    body = format_audit_report(findings)
+
+    run_command_safe(
+        [
+            "gh",
+            "label",
+            "create",
+            label,
+            "--description",
+            "Automated docs drift audit",
+            "--color",
+            "FBCA04",
+            "--force",
+        ],
+        check=False,
+        env={**os.environ, "GH_TOKEN": gh_token},
+    )
+
+    existing = run_command_safe(
+        [
+            "gh",
+            "issue",
+            "list",
+            "--label",
+            label,
+            "--state",
+            "open",
+            "--json",
+            "number",
+            "--limit",
+            "1",
+        ],
+        check=False,
+        env={**os.environ, "GH_TOKEN": gh_token},
+    )
+
+    try:
+        issues = json.loads(existing.stdout.strip()) if existing.returncode == 0 else []
+    except (json.JSONDecodeError, ValueError):
+        issues = []
+
+    if issues:
+        issue_num = issues[0]["number"]
+        run_command_safe(
+            ["gh", "issue", "edit", str(issue_num), "--body", body],
+            check=False,
+            env={**os.environ, "GH_TOKEN": gh_token},
+        )
+        print(f"Updated existing audit issue #{issue_num}")
+    else:
+        result = run_command_safe(
+            ["gh", "issue", "create", "--title", title, "--body", body, "--label", label],
+            check=False,
+            env={**os.environ, "GH_TOKEN": gh_token},
+        )
+        if result.returncode == 0:
+            print(f"Created audit issue: {result.stdout.strip()}")
diff --git a/src/suggest_docs.py b/src/suggest_docs.py
index 805f09d..139a903 100644
--- a/src/suggest_docs.py
+++ b/src/suggest_docs.py
@@ -258,6 +258,23 @@ def main():
         print(f"Index build complete: {result['status']}")
         return
 
+    # Handle audit mode (scheduled full-repo drift check)
+    mode = os.environ.get("MODE", "comment")
+    if mode == "audit":
+        from audit import format_audit_report, post_audit_issue, run_audit
+
+        print("Mode: audit")
+        if not setup_docs_environment():
+            print("Failed to set up docs environment")
+            return
+        budget = int(os.environ.get("AUDIT_BUDGET", "20"))
+        findings = run_audit(max_files=budget)
+        report = format_audit_report(findings)
+        print(report)
+        if findings and not args.dry_run:
+            post_audit_issue(findings)
+        return
+
     # Detect which command was used
     comment_body = os.environ.get("COMMENT_BODY", "")
 
diff --git a/tests/test_audit.py b/tests/test_audit.py
new file mode 100644
index 0000000..c224c23
--- /dev/null
+++ b/tests/test_audit.py
@@ -0,0 +1,26 @@
+"""Tests for audit.py -- scheduled drift audit."""
+
+from audit import format_audit_report
+
+
+class TestFormatAuditReport:
+    def test_no_findings(self):
+        assert "No documentation drift" in format_audit_report([])
+
+    def test_groups_by_severity(self):
+        findings = [
+            {"file": "a.md", "severity": "stale", "reason": "outdated"},
+            {"file": "b.md", "severity": "very-stale", "reason": "missing feature"},
+            {"file": "c.md", "severity": "stale", "reason": "old defaults"},
+        ]
+        report = format_audit_report(findings)
+        assert "## Very Stale (1 file)" in report
+        assert "## Stale (2 files)" in report
+        assert "b.md" in report
+        assert "a.md" in report
+
+    def test_skips_empty_groups(self):
+        findings = [{"file": "a.md", "severity": "stale", "reason": "outdated"}]
+        report = format_audit_report(findings)
+        assert "Very Stale" not in report
+        assert "Stale" in report