diff --git a/eval/harbor/clawcodex_agent.py b/eval/harbor/clawcodex_agent.py
index 40fe11df..0d5f915e 100644
--- a/eval/harbor/clawcodex_agent.py
+++ b/eval/harbor/clawcodex_agent.py
@@ -390,6 +390,7 @@ def __init__(
         advisor_effort: str | None = None,
         vision: str | None = None,
         nano: bool | str = False,
+        websearch: bool | str = False,
         *args,
         **kwargs,
     ):
@@ -406,6 +407,15 @@ def __init__(
             nano if isinstance(nano, bool)
             else parse_bool_env_value(str(nano).lower(), name="nano")
         )
+        # ``--ak websearch=1`` — opt nano into the WebSearch tool (seeded as
+        # config ``nano.websearch``; the tool additionally needs a resolvable
+        # TAVILY_API_KEY, which forward_keys carries by default). Mirrors
+        # pi's TB extension, whose websearch registers when the key is
+        # exported. No effect outside nano mode.
+        self._websearch = (
+            websearch if isinstance(websearch, bool)
+            else parse_bool_env_value(str(websearch).lower(), name="websearch")
+        )
         self._source = source
         # A ``source`` that resolves to a real file on the host is a
         # working-tree build to upload rather than a spec for uv to resolve
@@ -855,6 +865,11 @@ async def _seed_container_settings(
         config: dict[str, Any] = {}
         if settings:
             config["settings"] = settings
+        if self._websearch:
+            # Nano's explicit WebSearch opt-in (src/nano/registry.py
+            # _nano_websearch_configured) — key-presence alone must not
+            # grow the nano surface.
+            config["nano"] = {"websearch": True}
         env_block = self._host_env_keys()
         if env_block:
             config["env"] = env_block
diff --git a/eval/harbor/run_tb21_nano_max.sh b/eval/harbor/run_tb21_nano_max.sh
index 7802af3e..41ca96cc 100755
--- a/eval/harbor/run_tb21_nano_max.sh
+++ b/eval/harbor/run_tb21_nano_max.sh
@@ -63,6 +63,13 @@ if [ -n "${NANO_VISION:-}" ]; then
   AK_EXTRA+=(--ak "vision=$NANO_VISION")
   echo "vision: $NANO_VISION (nano registers vision_analyze)"
 fi
+# NANO_WEBSEARCH=1 opts nano into the WebSearch tool (needs a resolvable
+# TAVILY_API_KEY — forward_keys carries the host config env block by
+# default). Matches the pi TB extension's websearch.
+if [ "${NANO_WEBSEARCH:-0}" = "1" ]; then
+  AK_EXTRA+=(--ak websearch=1)
+  echo "websearch: enabled (nano registers WebSearch)"
+fi
 
 PYTHONPATH="$ROOT/eval/harbor" harbor run \
   --dataset terminal-bench/terminal-bench-2-1 \
diff --git a/src/nano/prompt.py b/src/nano/prompt.py
index ec13bfb6..0576ee41 100644
--- a/src/nano/prompt.py
+++ b/src/nano/prompt.py
@@ -46,12 +46,13 @@
     "Write": "create new files or fully overwrite existing ones",
     "Grep": "search file contents with regex (respects .gitignore)",
     "Glob": "find files by glob pattern",
-    # Conditional seventh tool — listed only when a vision model is
-    # configured and the registry registered it (see nano/registry.py).
+    # Conditional tools — listed only when configured and registered
+    # (see nano/registry.py).
     "vision_analyze": (
         "ask a configured vision model a question about a local image "
         "(screenshots, plots, photos, rendered output)"
     ),
+    "WebSearch": "search the web (titles, URLs, snippets)",
 }
 
 # The three non-tool guidelines at the end are distilled from clawcodex's
diff --git a/src/nano/registry.py b/src/nano/registry.py
index 22b5b734..99f4f49a 100644
--- a/src/nano/registry.py
+++ b/src/nano/registry.py
@@ -73,4 +73,35 @@ def build_nano_registry() -> ToolRegistry:
             registry.register(VisionAnalyzeTool)
     except Exception:  # noqa: BLE001 — a broken vision config never blocks nano
         pass
+    try:
+        from src.tool_system.tools import WebSearchTool
+
+        if _nano_websearch_configured() and WebSearchTool.is_enabled():
+            doc = NANO_TOOL_DOCS.get(WebSearchTool.name)
+            registry.register(
+                replace(WebSearchTool, prompt=lambda _doc=doc: _doc)
+                if doc else WebSearchTool
+            )
+    except Exception:  # noqa: BLE001 — a broken config never blocks nano
+        pass
     return registry
+
+
+def _nano_websearch_configured() -> bool:
+    """Explicit opt-in for WebSearch on the nano surface.
+
+    Reads global config ``nano.websearch is True`` (seeded by the harbor
+    adapter's ``--ak websearch=1``). Deliberately NOT keyed on the
+    TAVILY_API_KEY alone: keys are forwarded into benchmark containers by
+    default, and a key that happens to exist must not silently grow nano's
+    surface — the same explicitness bar as the vision config block. pi's
+    TB extension ships the same tool for the same reason (its runbook
+    exports TAVILY_API_KEY as a deliberate act).
+    """
+    try:
+        from src import config as cfg_mod
+
+        block = cfg_mod._get_default_manager().load_global().get("nano")
+        return isinstance(block, dict) and block.get("websearch") is True
+    except Exception:  # noqa: BLE001
+        return False
diff --git a/src/nano/tool_docs.py b/src/nano/tool_docs.py
index bc97c3a1..05c36d38 100644
--- a/src/nano/tool_docs.py
+++ b/src/nano/tool_docs.py
@@ -42,4 +42,11 @@
         "Finds files by glob pattern (e.g. '**/*.py'), sorted by "
         "modification time. Use for locating files by name or path shape."
     ),
+    # Conditional tool — registered only when explicitly opted in
+    # (nano.websearch config) AND a search key resolves; see registry.py.
+    "WebSearch": (
+        "Searches the web and returns result titles, URLs, and snippets. "
+        "Use for information you cannot derive locally (current versions, "
+        "external docs, error messages)."
+    ),
 }
diff --git a/tests/nano/test_nano_registry.py b/tests/nano/test_nano_registry.py
index 6a65f67d..ffffcc55 100644
--- a/tests/nano/test_nano_registry.py
+++ b/tests/nano/test_nano_registry.py
@@ -76,6 +76,27 @@ def test_vision_snippet_renders_in_prompt(vision_configured, tmp_path):
     assert "- vision_analyze: " in text
 
 
+def test_websearch_joins_only_when_opted_in(monkeypatch):
+    import src.nano.registry as registry_mod
+
+    monkeypatch.setattr(
+        registry_mod, "_nano_websearch_configured", lambda: True
+    )
+    names = [t.name for t in build_nano_registry().list_tools()]
+    assert names[-1] == "WebSearch"
+    ws = next(t for t in build_nano_registry().list_tools() if t.name == "WebSearch")
+    assert len(ws.prompt()) < 400  # pi-length doc override applied
+
+
+def test_websearch_absent_without_explicit_config():
+    # WebSearch.is_enabled defaults True (key errors surface at call
+    # time), so registration must hinge purely on the explicit
+    # nano.websearch config — a resolvable TAVILY key alone (the default
+    # forwarded-keys benchmark environment) must not grow the surface.
+    names = {t.name for t in build_nano_registry().list_tools()}
+    assert "WebSearch" not in names
+
+
 def test_default_registry_instances_untouched():
     # The nano registry carries copies; the shared static instances (and
     # therefore the default registry) must keep their full docs.