diff --git a/tests/test_routes_settings.py b/tests/test_routes_settings.py
index 0bdd9c5bb..4471b916e 100644
--- a/tests/test_routes_settings.py
+++ b/tests/test_routes_settings.py
@@ -330,3 +330,161 @@ async def test_result_fields_present(self, tmp_path):
         assert r.rebuilt is True
         assert r.success is False
         assert r.message == "x"
+
+
+class TestMemoryUrlSettings:
+    """Contract: GET /api/settings/memory-url returns {url, is_local, reachable}
+    and PUT probes the new target before returning (#1911)."""
+
+    @pytest.mark.asyncio
+    async def test_get_returns_default_url(self, client):
+        """Default URL is localhost:7900, is_local=True, reachable depends on env."""
+        resp = await client.get("/api/settings/memory-url")
+        assert resp.status_code == 200
+        data = resp.json()
+        assert data["url"] == "http://localhost:7900"
+        assert data["is_local"] is True
+        assert isinstance(data["reachable"], bool)
+
+    @pytest.mark.asyncio
+    async def test_get_returns_is_local_true_for_localhost(self, client, app):
+        """Setting the config URL to a loopback address must report is_local=True."""
+        app.state.config.memory_url = "http://127.0.0.1:7900"
+        resp = await client.get("/api/settings/memory-url")
+        assert resp.status_code == 200
+        data = resp.json()
+        assert data["url"] == "http://127.0.0.1:7900"
+        assert data["is_local"] is True
+
+    @pytest.mark.asyncio
+    async def test_get_returns_is_local_false_for_remote(self, client, app):
+        """A remote URL must report is_local=False."""
+        app.state.config.memory_url = "https://memory.example.com:7900"
+        resp = await client.get("/api/settings/memory-url")
+        assert resp.status_code == 200
+        data = resp.json()
+        assert data["url"] == "https://memory.example.com:7900"
+        assert data["is_local"] is False
+
+    @pytest.mark.asyncio
+    async def test_put_sets_url_and_probes(self, client, app):
+        """PUT persists the URL to config and returns probe result."""
+        resp = await client.put(
+            "/api/settings/memory-url",
+            json={"url": "http://192.168.1.100:7900"},
+        )
+        assert resp.status_code == 200
+        data = resp.json()
+        assert data["url"] == "http://192.168.1.100:7900"
+        assert data["is_local"] is True  # 192.168.x.x is private
+        assert isinstance(data["reachable"], bool)
+        # Verify it persisted on config
+        assert app.state.config.memory_url == "http://192.168.1.100:7900"
+
+    @pytest.mark.asyncio
+    async def test_put_rejects_empty_url(self, client):
+        """Empty URL must return 400."""
+        resp = await client.put(
+            "/api/settings/memory-url",
+            json={"url": ""},
+        )
+        assert resp.status_code == 400
+
+    @pytest.mark.asyncio
+    async def test_put_rejects_non_http_scheme(self, client):
+        """A non-http scheme must return 400."""
+        resp = await client.put(
+            "/api/settings/memory-url",
+            json={"url": "ftp://localhost:7900"},
+        )
+        assert resp.status_code == 400
+        assert "http" in resp.json()["error"].lower()
+
+    @pytest.mark.asyncio
+    async def test_get_reflects_put(self, client, app):
+        """After PUT, GET must return the new URL."""
+        await client.put(
+            "/api/settings/memory-url",
+            json={"url": "https://taosmd.local:8443"},
+        )
+        resp = await client.get("/api/settings/memory-url")
+        assert resp.status_code == 200
+        data = resp.json()
+        assert data["url"] == "https://taosmd.local:8443"
+        assert data["is_local"] is False
+
+    @pytest.mark.asyncio
+    async def test_is_local_url_helper(self):
+        """Unit-test _is_local_url directly."""
+        from tinyagentos.routes.settings import _is_local_url
+
+        assert _is_local_url("http://localhost:7900") is True
+        assert _is_local_url("http://127.0.0.1:7900") is True
+        assert _is_local_url("http://[::1]:7900") is True
+        assert _is_local_url("http://10.0.0.1:7900") is True   # private
+        assert _is_local_url("http://192.168.1.1:7900") is True  # private
+        assert _is_local_url("https://example.com:7900") is False
+        assert _is_local_url("http://8.8.8.8:7900") is False  # public IP
+
+    @pytest.mark.asyncio
+    async def test_put_probes_and_reports_unreachable(self, client):
+        """When taosmd is not running, reachable must be False."""
+        resp = await client.put(
+            "/api/settings/memory-url",
+            json={"url": "http://localhost:19999"},
+        )
+        assert resp.status_code == 200
+        data = resp.json()
+        assert data["reachable"] is False  # no taosmd on that port
+
+    @pytest.mark.asyncio
+    async def test_put_strips_trailing_slash(self, client, app):
+        """Trailing slash on the URL should be stripped."""
+        resp = await client.put(
+            "/api/settings/memory-url",
+            json={"url": "http://localhost:7900/"},
+        )
+        assert resp.status_code == 200
+        assert resp.json()["url"] == "http://localhost:7900"
+        assert app.state.config.memory_url == "http://localhost:7900"
+
+    @pytest.mark.asyncio
+    async def test_put_rejects_url_without_hostname(self, client):
+        """A URL without a valid hostname must return 400 (hostname check)."""
+        # path-only: http:///path  (hostname is empty string)
+        resp = await client.put(
+            "/api/settings/memory-url",
+            json={"url": "http:///path"},
+        )
+        assert resp.status_code == 400
+
+        # port-only: http://:7900  (hostname is empty, netloc non-empty — regression for netloc→hostname fix)
+        resp = await client.put(
+            "/api/settings/memory-url",
+            json={"url": "http://:7900"},
+        )
+        assert resp.status_code == 400
+
+    @pytest.mark.asyncio
+    async def test_put_response_includes_is_local_and_reachable(self, client):
+        """PUT response must include is_local and reachable alongside url."""
+        resp = await client.put(
+            "/api/settings/memory-url",
+            json={"url": "https://remote.example.com:7900"},
+        )
+        assert resp.status_code == 200
+        data = resp.json()
+        assert "url" in data
+        assert "is_local" in data
+        assert "reachable" in data
+        assert data["is_local"] is False  # remote hostname
+
+    @pytest.mark.asyncio
+    async def test_put_rejects_malformed_json(self, client):
+        """Malformed JSON body must return 422 (Pydantic validation), not 500."""
+        resp = await client.put(
+            "/api/settings/memory-url",
+            content=b"not json",
+            headers={"Content-Type": "application/json"},
+        )
+        assert resp.status_code == 422
diff --git a/tinyagentos/routes/settings.py b/tinyagentos/routes/settings.py
index e4c611e15..c904b4334 100644
--- a/tinyagentos/routes/settings.py
+++ b/tinyagentos/routes/settings.py
@@ -1,12 +1,15 @@
 from __future__ import annotations
 import asyncio
 import datetime
+import httpx
 import io
+import ipaddress
 import logging
 import os
 import shutil
 import tarfile
 import time
+from collections import OrderedDict
 from pathlib import Path
 from urllib.parse import urlparse
 
@@ -1075,31 +1078,92 @@ async def set_update_channel(request: Request, body: UpdateChannel):
 # Memory URL (taOSmd)
 # ---------------------------------------------------------------------------
 
+_MEMORY_URL_PROBE_CACHE: OrderedDict = OrderedDict()  # {url: (timestamp, bool)} — capped at 32 entries via FIFO eviction
+
+
+def _is_local_url(url: str) -> bool:
+    """Return True if *url* points to the local machine (loopback or private)."""
+    parsed = urlparse(url)
+    hostname = parsed.hostname
+    if not hostname:
+        return False
+    if hostname in ("localhost", "127.0.0.1", "::1"):
+        return True
+    try:
+        addr = ipaddress.ip_address(hostname)
+        return addr.is_loopback or addr.is_private
+    except ValueError:
+        return False
+
+
+async def _probe_taosmd(request: Request, url: str) -> bool:
+    """Probe the taOSmd /health endpoint.  Returns True if reachable."""
+    try:
+        client = request.app.state.http_client
+        resp = await client.get(
+            f"{url}/health",
+            timeout=httpx.Timeout(3.0, connect=2.0),
+        )
+        return resp.status_code == 200
+    except (httpx.RequestError, httpx.InvalidURL):
+        return False
+
+
 class MemoryUrlUpdate(BaseModel):
     url: str
 
 
 @router.get("/api/settings/memory-url")
 async def get_memory_url(request: Request):
-    """Return the current taOSmd memory URL."""
+    """Return the current taOSmd memory URL with local/reachable probes."""
     config = request.app.state.config
-    return {"url": config.memory_url}
+    url = config.memory_url
+    is_local = _is_local_url(url)
+
+    # Return cached probe result if fresh (< 30 s), else re-probe.
+    cached = _MEMORY_URL_PROBE_CACHE.get(url)
+    now = time.monotonic()
+    if cached and (now - cached[0]) < 30:
+        reachable = cached[1]
+    else:
+        reachable = await _probe_taosmd(request, url)
+        _MEMORY_URL_PROBE_CACHE[url] = (now, reachable)
+        if len(_MEMORY_URL_PROBE_CACHE) > 32:
+            _MEMORY_URL_PROBE_CACHE.popitem(last=False)
+
+    return {"url": url, "is_local": is_local, "reachable": reachable}
 
 
 @router.put("/api/settings/memory-url")
 async def set_memory_url(request: Request, body: MemoryUrlUpdate):
-    """Update the taOSmd memory URL and persist to config."""
+    """Update the taOSmd memory URL, persist to config, and probe reachability.
+
+    The URL is always accepted and persisted.  The *reachable* field reports
+    the probe result but does not gate the save."""
     url = body.url.strip()
     if not url:
         return JSONResponse({"error": "URL must not be empty"}, status_code=400)
+    # Strip a single trailing slash (not a character set).
+    if url.endswith("/"):
+        url = url[:-1]
     parsed = urlparse(url)
     if parsed.scheme not in ("http", "https"):
         return JSONResponse({"error": "URL must use http:// or https:// scheme"}, status_code=400)
-    if not parsed.netloc:
+    if not parsed.hostname:
         return JSONResponse({"error": "URL must include a hostname"}, status_code=400)
+
+    is_local = _is_local_url(url)
+    reachable = await _probe_taosmd(request, url)
+
     config = request.app.state.config
     config.memory_url = url
     await save_config_locked(config, request.app.state.config_path)
     # Keep app.state.taosmd_url in sync for runtime access
     request.app.state.taosmd_url = url
-    return {"status": "saved", "url": url}
+
+    # Cache the probe result so the next GET is instant.
+    _MEMORY_URL_PROBE_CACHE[url] = (time.monotonic(), reachable)
+    if len(_MEMORY_URL_PROBE_CACHE) > 32:
+        _MEMORY_URL_PROBE_CACHE.popitem(last=False)
+
+    return {"url": url, "is_local": is_local, "reachable": reachable}