diff --git a/pkg-py/src/querychat/querychat.py b/pkg-py/src/querychat/querychat.py
index 3f6ea616..5b142576 100644
--- a/pkg-py/src/querychat/querychat.py
+++ b/pkg-py/src/querychat/querychat.py
@@ -224,11 +224,20 @@ def df_to_html(df: IntoFrame, maxrows: int = 5) -> str:
         HTML string representation of the table
 
     """
+    # Convert to Narwhals DataFrame if it's not already one
     if isinstance(df, (nw.LazyFrame, nw.DataFrame)):
-        df_short = df.lazy().head(maxrows).collect()
-        nrow_full = df.lazy().select(nw.len()).collect().item()
+        nw_df = df
     else:
-        raise TypeError("df must be a Narwhals DataFrame or LazyFrame")
+        # Try to convert using nw.from_native (supports pandas and other formats)
+        try:
+            nw_df = nw.from_native(df)
+        except Exception as e:
+            raise TypeError(
+                "df must be a Narwhals DataFrame, LazyFrame, or compatible DataFrame (e.g., pandas)",
+            ) from e
+
+    df_short = nw_df.lazy().head(maxrows).collect()
+    nrow_full = nw_df.lazy().select(nw.len()).collect().item()
 
     # Generate HTML table
     table_html = df_short.to_pandas().to_html(
diff --git a/pkg-py/tests/test_query_function.py b/pkg-py/tests/test_query_function.py
new file mode 100644
index 00000000..982efacd
--- /dev/null
+++ b/pkg-py/tests/test_query_function.py
@@ -0,0 +1,116 @@
+import sqlite3
+import tempfile
+from pathlib import Path
+
+import pandas as pd
+import pytest
+from sqlalchemy import create_engine
+from src.querychat.datasource import DataFrameSource, SQLAlchemySource
+from src.querychat.querychat import df_to_html
+
+
+@pytest.fixture
+def sample_dataframe():
+    """Create a sample pandas DataFrame for testing."""
+    return pd.DataFrame(
+        {
+            "id": [1, 2, 3, 4, 5],
+            "name": ["Alice", "Bob", "Charlie", "Diana", "Eve"],
+            "age": [25, 30, 35, 28, 32],
+            "salary": [50000, 60000, 70000, 55000, 65000],
+        },
+    )
+
+
+@pytest.fixture
+def test_db_engine_with_data():
+    """Create a temporary SQLite database with test data."""
+    temp_db = tempfile.NamedTemporaryFile(delete=False, suffix=".db")  # noqa: SIM115
+    temp_db.close()
+
+    conn = sqlite3.connect(temp_db.name)
+    cursor = conn.cursor()
+
+    cursor.execute("""
+        CREATE TABLE employees (
+            id INTEGER PRIMARY KEY,
+            name TEXT,
+            age INTEGER,
+            salary REAL
+        )
+    """)
+
+    test_data = [
+        (1, "Alice", 25, 50000),
+        (2, "Bob", 30, 60000),
+        (3, "Charlie", 35, 70000),
+        (4, "Diana", 28, 55000),
+        (5, "Eve", 32, 65000),
+    ]
+
+    cursor.executemany(
+        "INSERT INTO employees (id, name, age, salary) VALUES (?, ?, ?, ?)",
+        test_data,
+    )
+
+    conn.commit()
+    conn.close()
+
+    engine = create_engine(f"sqlite:///{temp_db.name}")
+    yield engine
+
+    # Cleanup
+    Path(temp_db.name).unlink()
+
+
+def test_df_to_html_with_dataframe_source_result(sample_dataframe):
+    """Test that df_to_html() works with results from DataFrameSource.execute_query()."""
+    source = DataFrameSource(sample_dataframe, "employees")
+
+    # Execute query to get pandas DataFrame
+    result_df = source.execute_query("SELECT * FROM employees WHERE age > 25")
+
+    # This should succeed after the fix
+    html_output = df_to_html(result_df)
+
+    # Verify the HTML contains expected content
+    assert isinstance(html_output, str)
+    assert "<table" in html_output
+    assert "Bob" in html_output
+    assert "Charlie" in html_output
+    assert "Diana" in html_output
+    assert "Eve" in html_output
+
+
+def test_df_to_html_with_sqlalchemy_source_result(test_db_engine_with_data):
+    """Test that df_to_html() works with results from SQLAlchemySource.execute_query()."""
+    source = SQLAlchemySource(test_db_engine_with_data, "employees")
+
+    # Execute query to get pandas DataFrame
+    result_df = source.execute_query("SELECT * FROM employees WHERE age > 25")
+
+    # This should succeed after the fix
+    html_output = df_to_html(result_df)
+
+    # Verify the HTML contains expected content
+    assert isinstance(html_output, str)
+    assert "<table" in html_output
+    assert "Bob" in html_output
+    assert "Charlie" in html_output
+    assert "Diana" in html_output
+    assert "Eve" in html_output
+
+
+def test_df_to_html_with_truncation(sample_dataframe):
+    """Test that df_to_html() properly truncates large datasets."""
+    source = DataFrameSource(sample_dataframe, "employees")
+
+    # Execute query to get all rows
+    result_df = source.execute_query("SELECT * FROM employees")
+
+    # Test with maxrows=3 to trigger truncation
+    html_output = df_to_html(result_df, maxrows=3)
+
+    # Should show truncation message
+    assert "Showing only the first 3 rows out of 5" in html_output
+    assert "<table" in html_output