diff --git a/test/web_interface/test_cache.py b/test/web_interface/test_cache.py
new file mode 100644
index 00000000..98986b0c
--- /dev/null
+++ b/test/web_interface/test_cache.py
@@ -0,0 +1,38 @@
+"""Tests for the web interface's in-memory cache helpers."""
+import pytest
+
+from web_interface.cache import delete_cached, get_cached, invalidate_cache, set_cached
+
+
+@pytest.fixture(autouse=True)
+def clean_cache():
+    invalidate_cache()
+    yield
+    invalidate_cache()
+
+
+def test_set_and_get():
+    set_cached('key', 'value')
+    assert get_cached('key') == 'value'
+
+
+def test_get_missing_returns_none():
+    assert get_cached('missing') is None
+
+
+def test_delete_cached_removes_key():
+    set_cached('fonts_catalog', ['a-font'])
+    delete_cached('fonts_catalog')
+    assert get_cached('fonts_catalog') is None
+
+
+def test_delete_cached_missing_key_is_noop():
+    delete_cached('never-set')  # must not raise
+
+
+def test_invalidate_cache_pattern():
+    set_cached('fonts_catalog', 1)
+    set_cached('plugins_list', 2)
+    invalidate_cache('fonts')
+    assert get_cached('fonts_catalog') is None
+    assert get_cached('plugins_list') == 2
diff --git a/web_interface/cache.py b/web_interface/cache.py
index c1b7d321..f7aad3ea 100644
--- a/web_interface/cache.py
+++ b/web_interface/cache.py
@@ -29,6 +29,12 @@ def set_cached(key: str, value: Any, ttl_seconds: int = 60) -> None:
     _cache_timestamps[key] = time.time()
 
 
+def delete_cached(key: str) -> None:
+    """Remove a single key from the cache if present."""
+    _cache.pop(key, None)
+    _cache_timestamps.pop(key, None)
+
+
 def invalidate_cache(pattern: Optional[str] = None) -> None:
     """Invalidate cache entries matching pattern, or all if pattern is None."""
     if pattern is None: