diff --git a/plugins/memory/hindsight/__init__.py b/plugins/memory/hindsight/__init__.py
index 40772f79d8a0..20f338562d0e 100644
--- a/plugins/memory/hindsight/__init__.py
+++ b/plugins/memory/hindsight/__init__.py
@@ -611,6 +611,88 @@ def is_available(self) -> bool:
         except Exception:
             return False
 
+    def health_check(self) -> tuple[bool, str]:
+        """Mode-dependent probe.
+
+        local / local_embedded:
+          (True, "") if the local Hindsight stack imports cleanly.
+          (False, "sdk_missing: <exc>") otherwise.
+
+        local_external / cloud:
+          GET <api_url>/version with the configured key.
+          (True, "")                  — 200 + parseable JSON.
+          (False, "no_credentials")   — neither apiKey nor api_url
+                                         is set (cloud only — for
+                                         local_external the api_url
+                                         is required and absence is
+                                         classified as no_url).
+          (False, "no_url")           — local_external without an
+                                         api_url.
+          (False, "auth: ...")        — 401 / 403.
+          (False, "not_found: ...")   — 404.
+          (False, "http: ...")        — other non-2xx.
+          (False, "unreachable: ...") — connection / timeout / parse.
+
+        Top-level config load failure → (False, "config_error: <exc>").
+        MUST NOT raise.
+        """
+        try:
+            cfg = _load_config()
+        except Exception as exc:  # noqa: BLE001
+            return (False, f"config_error: {exc}")
+        mode = cfg.get("mode", "cloud")
+
+        # ── local modes: import probe only ──────────────────
+        if mode in {"local", "local_embedded"}:
+            ok, exc_msg = _check_local_runtime()
+            if ok:
+                return (True, "")
+            return (False, f"sdk_missing: {(exc_msg or 'import failed')[:200]}")
+
+        # ── url-based modes (cloud / local_external) ────────
+        api_url = (cfg.get("api_url")
+                   or os.environ.get("HINDSIGHT_API_URL", "")).strip()
+        api_key = (cfg.get("apiKey")
+                   or cfg.get("api_key")
+                   or os.environ.get("HINDSIGHT_API_KEY", "")).strip()
+
+        if mode == "local_external":
+            if not api_url:
+                return (False, "no_url")
+        else:
+            # cloud
+            if not (api_url or api_key):
+                return (False, "no_credentials")
+            if not api_url:
+                # api_key set but no URL — most cloud deployments
+                # need both. Treat as a config error pointing at
+                # the missing URL.
+                return (False, "no_url")
+
+        import urllib.error
+        import urllib.request
+        url = api_url.rstrip("/") + "/version"
+        req = urllib.request.Request(url)
+        if api_key:
+            req.add_header("Authorization", f"Bearer {api_key}")
+        try:
+            with urllib.request.urlopen(req, timeout=5.0) as resp:
+                payload = resp.read().decode("utf-8", errors="replace")
+            data = json.loads(payload)
+            if not isinstance(data, dict):
+                return (False, f"unreachable: /version returned non-dict")
+            return (True, "")
+        except urllib.error.HTTPError as exc:
+            if exc.code in (401, 403):
+                return (False, f"auth: HTTP {exc.code} from {url}")
+            if exc.code == 404:
+                return (False, f"not_found: HTTP 404 from {url}")
+            return (False, f"http: HTTP {exc.code} from {url}")
+        except (urllib.error.URLError, OSError, TimeoutError) as exc:
+            return (False, f"unreachable: {str(exc)[:200]}")
+        except Exception as exc:  # noqa: BLE001
+            return (False, f"unreachable: {str(exc)[:200]}")
+
     def save_config(self, values, hermes_home):
         """Write config to $HERMES_HOME/hindsight/config.json."""
         import json
diff --git a/tests/plugins/memory/test_hindsight_health_check.py b/tests/plugins/memory/test_hindsight_health_check.py
new file mode 100644
index 000000000000..1faef76f25a1
--- /dev/null
+++ b/tests/plugins/memory/test_hindsight_health_check.py
@@ -0,0 +1,230 @@
+"""Tests for ``HindsightMemoryProvider.health_check`` (#42 step 2g).
+
+The override dispatches by config `mode` — local modes do an
+import probe; cloud / local_external modes hit `<api_url>/version`.
+Reasons follow the RFC #42 prefix taxonomy.
+"""
+from __future__ import annotations
+
+import io
+import json
+import sys
+import urllib.error
+from types import SimpleNamespace
+
+import pytest
+
+import plugins.memory.hindsight as hs
+from plugins.memory.hindsight import HindsightMemoryProvider
+
+
+# ── Helpers ────────────────────────────────────────────────────
+
+
+def _stub_config(monkeypatch, **cfg):
+    monkeypatch.setattr(hs, "_load_config", lambda: cfg)
+
+
+def _stub_local_runtime(monkeypatch, *, available: bool,
+                        error: str | None = None):
+    monkeypatch.setattr(
+        hs, "_check_local_runtime",
+        lambda: (available, error))
+
+
+def _stub_urlopen(monkeypatch, *, response_payload=None,
+                   raises=None):
+    """Replace urllib.request.urlopen with a fake. response_payload
+    is bytes returned by .read(); raises is an exception to throw."""
+    import urllib.request as _ur
+
+    class _Resp:
+        def __init__(self, payload):
+            self._payload = payload
+
+        def __enter__(self):
+            return self
+
+        def __exit__(self, *exc):
+            return False
+
+        def read(self):
+            return self._payload
+
+    def _urlopen(req, timeout=None):
+        if raises is not None:
+            raise raises
+        return _Resp(
+            response_payload if response_payload is not None
+            else json.dumps({"version": "0.5.6"}).encode("utf-8"))
+
+    monkeypatch.setattr(_ur, "urlopen", _urlopen)
+
+
+# ── Local modes ────────────────────────────────────────────────
+
+
+def test_local_returns_true_when_runtime_imports(monkeypatch):
+    _stub_config(monkeypatch, mode="local")
+    _stub_local_runtime(monkeypatch, available=True)
+    healthy, reason = HindsightMemoryProvider().health_check()
+    assert healthy is True
+    assert reason == ""
+
+
+def test_local_embedded_returns_true_when_runtime_imports(monkeypatch):
+    _stub_config(monkeypatch, mode="local_embedded")
+    _stub_local_runtime(monkeypatch, available=True)
+    healthy, reason = HindsightMemoryProvider().health_check()
+    assert healthy is True
+    assert reason == ""
+
+
+def test_local_returns_sdk_missing_when_import_fails(monkeypatch):
+    _stub_config(monkeypatch, mode="local")
+    _stub_local_runtime(monkeypatch, available=False,
+                        error="numpy ABI mismatch on this CPU")
+    healthy, reason = HindsightMemoryProvider().health_check()
+    assert healthy is False
+    assert reason.startswith("sdk_missing:")
+    assert "numpy ABI mismatch" in reason
+
+
+# ── local_external (URL but no key required) ───────────────────
+
+
+def test_local_external_no_url_returns_no_url(monkeypatch):
+    _stub_config(monkeypatch, mode="local_external")
+    monkeypatch.delenv("HINDSIGHT_API_URL", raising=False)
+    healthy, reason = HindsightMemoryProvider().health_check()
+    assert healthy is False
+    assert reason == "no_url"
+
+
+def test_local_external_with_url_probes_version(monkeypatch):
+    _stub_config(monkeypatch, mode="local_external",
+                 api_url="http://hindsight-local:9999")
+    _stub_urlopen(monkeypatch)
+    healthy, reason = HindsightMemoryProvider().health_check()
+    assert healthy is True
+
+
+# ── Cloud mode ─────────────────────────────────────────────────
+
+
+def test_cloud_no_credentials_when_both_empty(monkeypatch):
+    _stub_config(monkeypatch, mode="cloud")
+    monkeypatch.delenv("HINDSIGHT_API_KEY", raising=False)
+    monkeypatch.delenv("HINDSIGHT_API_URL", raising=False)
+    healthy, reason = HindsightMemoryProvider().health_check()
+    assert healthy is False
+    assert reason == "no_credentials"
+
+
+def test_cloud_no_url_when_only_key(monkeypatch):
+    _stub_config(monkeypatch, mode="cloud", apiKey="real-key")
+    monkeypatch.delenv("HINDSIGHT_API_URL", raising=False)
+    healthy, reason = HindsightMemoryProvider().health_check()
+    assert healthy is False
+    assert reason == "no_url"
+
+
+def test_cloud_success(monkeypatch):
+    _stub_config(monkeypatch, mode="cloud", apiKey="real",
+                 api_url="https://api.hindsight.test")
+    _stub_urlopen(monkeypatch)
+    healthy, reason = HindsightMemoryProvider().health_check()
+    assert healthy is True
+
+
+def test_cloud_auth_401(monkeypatch):
+    _stub_config(monkeypatch, mode="cloud", apiKey="wrong",
+                 api_url="https://api.hindsight.test")
+    _stub_urlopen(monkeypatch,
+                   raises=urllib.error.HTTPError(
+                       "http://x/version", 401, "Unauthorized",
+                       {}, None))
+    healthy, reason = HindsightMemoryProvider().health_check()
+    assert healthy is False
+    assert reason.startswith("auth:")
+    assert "401" in reason
+
+
+def test_cloud_404_is_not_found(monkeypatch):
+    _stub_config(monkeypatch, mode="cloud", apiKey="k",
+                 api_url="https://api.hindsight.test")
+    _stub_urlopen(monkeypatch,
+                   raises=urllib.error.HTTPError(
+                       "http://x/version", 404, "NF", {}, None))
+    healthy, reason = HindsightMemoryProvider().health_check()
+    assert healthy is False
+    assert reason.startswith("not_found:")
+    assert "404" in reason
+
+
+def test_cloud_other_http_classified_as_http(monkeypatch):
+    _stub_config(monkeypatch, mode="cloud", apiKey="k",
+                 api_url="https://api.hindsight.test")
+    _stub_urlopen(monkeypatch,
+                   raises=urllib.error.HTTPError(
+                       "http://x/version", 503, "Down", {}, None))
+    healthy, reason = HindsightMemoryProvider().health_check()
+    assert healthy is False
+    assert reason.startswith("http:")
+    assert "503" in reason
+
+
+def test_cloud_connection_refused_classified_as_unreachable(monkeypatch):
+    _stub_config(monkeypatch, mode="cloud", apiKey="k",
+                 api_url="https://api.hindsight.test")
+    _stub_urlopen(monkeypatch,
+                   raises=urllib.error.URLError("connection refused"))
+    healthy, reason = HindsightMemoryProvider().health_check()
+    assert healthy is False
+    assert reason.startswith("unreachable:")
+    assert "connection refused" in reason
+
+
+def test_cloud_malformed_response_classified_as_unreachable(
+        monkeypatch):
+    _stub_config(monkeypatch, mode="cloud", apiKey="k",
+                 api_url="https://api.hindsight.test")
+    _stub_urlopen(monkeypatch, response_payload=b"not json")
+    healthy, reason = HindsightMemoryProvider().health_check()
+    assert healthy is False
+    assert reason.startswith("unreachable:")
+
+
+def test_cloud_non_dict_json_classified_as_unreachable(monkeypatch):
+    _stub_config(monkeypatch, mode="cloud", apiKey="k",
+                 api_url="https://api.hindsight.test")
+    _stub_urlopen(monkeypatch, response_payload=b'["array", "not", "dict"]')
+    healthy, reason = HindsightMemoryProvider().health_check()
+    assert healthy is False
+    assert reason.startswith("unreachable:")
+    assert "non-dict" in reason
+
+
+# ── Top-level config failure ──────────────────────────────────
+
+
+def test_config_error_when_load_config_raises(monkeypatch):
+    monkeypatch.setattr(
+        hs, "_load_config",
+        lambda: (_ for _ in ()).throw(RuntimeError("config corrupted")))
+    healthy, reason = HindsightMemoryProvider().health_check()
+    assert healthy is False
+    assert reason.startswith("config_error:")
+    assert "config corrupted" in reason
+
+
+# ── Env-var fallback ──
+
+
+def test_env_vars_used_when_config_missing_keys(monkeypatch):
+    _stub_config(monkeypatch, mode="cloud")  # No api_url/apiKey in cfg
+    monkeypatch.setenv("HINDSIGHT_API_KEY", "env-key")
+    monkeypatch.setenv("HINDSIGHT_API_URL", "https://env.test")
+    _stub_urlopen(monkeypatch)
+    healthy, reason = HindsightMemoryProvider().health_check()
+    assert healthy is True