diff --git a/tests/test_tool_snippet_limit_parity.py b/tests/test_tool_snippet_limit_parity.py
new file mode 100644
index 00000000..6157d871
--- /dev/null
+++ b/tests/test_tool_snippet_limit_parity.py
@@ -0,0 +1,11 @@
+"""Regression test: JS tool-result snippet limit matches the Python backend limit."""
+from pathlib import Path
+
+REPO = Path(__file__).resolve().parent.parent
+
+
+def test_tool_snippet_limit_parity():
+    py = (REPO / "api" / "streaming.py").read_text(encoding="utf-8")
+    js = (REPO / "static" / "ui.js").read_text(encoding="utf-8")
+    assert "_TOOL_RESULT_SNIPPET_MAX = 4000" in py
+    assert ".slice(0,4000)" in js