diff --git a/src/endpoints.py b/src/endpoints.py
index 346b1b4..a44f6a5 100644
--- a/src/endpoints.py
+++ b/src/endpoints.py
@@ -153,10 +153,25 @@ async def read_item(request: LinkRequest, dep: BrowserDep) -> LinkResponse:
             else await dep.page.content()
         )
 
+    # The User-Agent the target site actually saw, taken from the navigation
+    # request headers. page.evaluate falls through to eval() in the page's
+    # main world and fails whenever the page CSP disallows eval (e.g. the
+    # Firefox JSON viewer in #394, or uncatchable meta-tag CSP), so evaluate
+    # is only a fallback and its failure must not turn the request into a 500.
+    user_agent = (
+        page_request.request.headers.get("user-agent") if page_request else None
+    )
+    if user_agent is None:
+        try:
+            user_agent = await dep.page.evaluate("navigator.userAgent")
+        except Exception:
+            logger.warning("Could not determine User-Agent via page.evaluate")
+            user_agent = ""
+
     return LinkResponse(
         message="Success",
         solution=Solution(
-            user_agent=await dep.page.evaluate("navigator.userAgent"),
+            user_agent=user_agent,
             url=final_url if final_url is not None else dep.page.url,
             status=status,
             cookies=cookies,
diff --git a/tests/main_test.py b/tests/main_test.py
index cc8a5dd..06bc993 100644
--- a/tests/main_test.py
+++ b/tests/main_test.py
@@ -139,7 +139,9 @@ def fake_dep(*, fail_states: set[str] | None = None) -> BrowserDepClass:
     page = AsyncMock()
     page.url = "https://example.test/login"
     page.goto.return_value = MagicMock(
-        status=HTTPStatus.OK, headers={"content-type": "text/html"}
+        status=HTTPStatus.OK,
+        headers={"content-type": "text/html"},
+        request=MagicMock(headers={"user-agent": "UnitTestBrowser/1.0"}),
     )
     page.title.return_value = "Login"
     page.evaluate.return_value = "UnitTestBrowser/1.0"
@@ -181,3 +183,22 @@ async def test_domcontentloaded_timeout_returns_408():
         )
 
     assert exc.value.status_code == HTTPStatus.REQUEST_TIMEOUT
+
+
+@pytest.mark.asyncio
+async def test_user_agent_survives_csp_blocked_evaluate():
+    """UA comes from request headers when page CSP blocks evaluate (#394).
+
+    No CSP configuration (header, meta tag, or internal viewer document) may
+    turn /v1 into a 500.
+    """
+    dep = fake_dep()
+    dep.page.evaluate.side_effect = Exception("call to eval() blocked by CSP")
+
+    response = await read_item(
+        LinkRequest(url="https://example.test/login"),
+        dep,
+    )
+
+    assert response.status == "ok"
+    assert response.solution.user_agent == "UnitTestBrowser/1.0"