diff --git a/runtime/tools/public/attachment_local_url_tool.py b/runtime/tools/public/attachment_local_url_tool.py
new file mode 100644
index 00000000..b2de9fa9
--- /dev/null
+++ b/runtime/tools/public/attachment_local_url_tool.py
@@ -0,0 +1,59 @@
+from __future__ import annotations
+
+import re
+from typing import Any
+from pathlib import Path
+
+from oclaw.platform.files.attachment_assets import AttachmentAssetStore
+from oclaw.runtime.tools.base import ToolSpec
+
+_ATTACHMENT_ID_RE = re.compile(r"^[a-f0-9]{64}$")
+
+
+def attachment_local_url_tool() -> ToolSpec:
+    def _handler(args: dict[str, Any]) -> dict[str, Any]:
+        attachment_id = str(args.get("attachment_id") or "").strip().lower()
+        if not attachment_id:
+            return {"ok": False, "error": "attachment_id_required"}
+        if not _ATTACHMENT_ID_RE.fullmatch(attachment_id):
+            return {"ok": False, "error": "attachment_id_invalid"}
+
+        store = AttachmentAssetStore()
+        meta = store.get_meta(attachment_id)
+        local_path = store.get_local_path(attachment_id)
+        local_path_text = str(local_path) if local_path else ""
+        file_url = Path(local_path).resolve().as_uri() if local_path else ""
+
+        return {
+            "ok": True,
+            "attachment_id": attachment_id,
+            "exists": bool(meta or local_path),
+            # For direct rendering in desktop/electron contexts, prefer file URL first.
+            "preferred_url": file_url or local_path_text,
+            "mime": str(getattr(meta, "mime", "") or ""),
+            "name": str(getattr(meta, "name", "") or ""),
+            "bytes": int(getattr(meta, "bytes", 0) or 0),
+            "local_path": local_path_text,
+            "file_url": file_url,
+        }
+
+    return ToolSpec(
+        name="attachment_local_url",
+        description="Resolve attachment_id to local download URL under this oclaw gateway.",
+        parameters={
+            "type": "object",
+            "properties": {
+                "attachment_id": {"type": "string", "description": "Stored attachment id."},
+            },
+            "required": ["attachment_id"],
+            "additionalProperties": False,
+        },
+        handler=_handler,
+        read_only=True,
+        tags=frozenset({"attachment", "url", "read"}),
+        risk_level="low",
+        timeout_s=2.0,
+    )
+
+
+__all__ = ["attachment_local_url_tool"]
diff --git a/tests/test_attachment_local_url_public_tool.py b/tests/test_attachment_local_url_public_tool.py
new file mode 100644
index 00000000..512d1235
--- /dev/null
+++ b/tests/test_attachment_local_url_public_tool.py
@@ -0,0 +1,50 @@
+from __future__ import annotations
+
+from pathlib import Path
+
+from oclaw.runtime.tools.public.attachment_local_url_tool import attachment_local_url_tool
+
+
+class _FakeMeta:
+    mime = "image/png"
+    name = "cat.png"
+    bytes = 123
+
+
+class _FakeStore:
+    def get_meta(self, attachment_id: str) -> _FakeMeta | None:
+        if attachment_id.startswith("a"):
+            return _FakeMeta()
+        return None
+
+    def get_local_path(self, attachment_id: str) -> Path | None:
+        if attachment_id.startswith("a"):
+            return Path("D:/project/chatgpt/oclaw/data/attachments/aa/bb/cat.png")
+        return None
+
+
+def test_attachment_local_url_rejects_invalid_id() -> None:
+    spec = attachment_local_url_tool()
+    out = spec.handler({"attachment_id": "bad-id"})
+    assert out.get("ok") is False
+    assert out.get("error") == "attachment_id_invalid"
+
+
+def test_attachment_local_url_builds_absolute_url(monkeypatch) -> None:
+    monkeypatch.setattr("oclaw.runtime.tools.public.attachment_local_url_tool.AttachmentAssetStore", _FakeStore)
+    spec = attachment_local_url_tool()
+    aid = "a" * 64
+    out = spec.handler({"attachment_id": aid})
+    assert out.get("ok") is True
+    assert out.get("exists") is True
+    assert str(out.get("local_path") or "").endswith("cat.png")
+    assert str(out.get("file_url") or "").startswith("file:///")
+    assert out.get("preferred_url") == out.get("file_url")
+    assert out.get("mime") == "image/png"
+
+
+def test_attachment_local_url_is_visible_in_public_registry() -> None:
+    from oclaw.runtime.tools.catalog import default_registry
+
+    names = [t.name for t in default_registry(expert="network_ops+memory", specialist="ops").list()]
+    assert "attachment_local_url" in names