diff --git a/tools/runtime_path_audit.py b/tools/runtime_path_audit.py
new file mode 100644
index 00000000..60443555
--- /dev/null
+++ b/tools/runtime_path_audit.py
@@ -0,0 +1,79 @@
+#!/usr/bin/env python3
+"""Audit MACA-related path variables for missing, duplicate, and stale entries."""
+
+from __future__ import annotations
+
+import argparse
+import json
+import os
+from pathlib import Path
+
+ENV_VARS = ["MACA_HOME", "LD_LIBRARY_PATH", "PYTHONPATH"]
+
+
+def split_paths(value: str) -> list[str]:
+    parts: list[str] = []
+    for chunk in value.replace(";", os.pathsep).split(os.pathsep):
+        chunk = chunk.strip()
+        if chunk:
+            parts.append(chunk)
+    return parts
+
+
+def normalize_path(raw: str) -> str:
+    return os.path.normpath(os.path.abspath(os.path.expanduser(raw)))
+
+
+def audit(env: dict[str, str]) -> dict[str, object]:
+    findings: list[dict[str, str]] = []
+    for name in ENV_VARS:
+        seen: set[str] = set()
+        for raw in split_paths(env.get(name, "")):
+            normalized = normalize_path(raw)
+            if normalized in seen:
+                findings.append(
+                    {
+                        "env": name,
+                        "path": raw,
+                        "severity": "warning",
+                        "message": "duplicate path entry",
+                    }
+                )
+            seen.add(normalized)
+            if not Path(normalized).exists():
+                findings.append(
+                    {
+                        "env": name,
+                        "path": raw,
+                        "severity": "info",
+                        "message": "path does not exist in this container",
+                    }
+                )
+    return {"finding_count": len(findings), "findings": findings}
+
+
+def self_test() -> None:
+    missing = os.pathsep.join(["/definitely_missing", "/definitely_missing"])
+    data = audit({"LD_LIBRARY_PATH": missing})
+    if data["finding_count"] < 2:
+        raise RuntimeError(f"self-test failed: {data}")
+    print(
+        json.dumps(
+            {"ok": True, "finding_count": data["finding_count"]}, ensure_ascii=False
+        )
+    )
+
+
+def main() -> int:
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("--self-test", action="store_true")
+    args = parser.parse_args()
+    if args.self_test:
+        self_test()
+        return 0
+    print(json.dumps(audit(dict(os.environ)), ensure_ascii=False, indent=2))
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())