From the forums we found out a discreapancy between the Streamlit embedded app for Altair chart and the relevant Altair code.

The code reads :

c = alt.Chart(df).mark_circle().encode(x='a', y='b', size='c', color='c')

so there is no tooltip, but in the embedded app there is a tooltip appearing.

so I guess the correct code should read :

c = alt.Chart(df).mark_circle().encode(x='a', y='b', size='c', color='c', tooltip=['a', 'b', 'c'])

if we don't want to modify the embedded app.

Link to doc page in question (if any):

All the links that point to the same Streamlit embedded app :

• https://docs.streamlit.io/api.html#streamlit.altair_chart
• https://docs.streamlit.io/api.html#streamlit.write
• https://docs.streamlit.io/api.html#streamlit.vega_lite_chart

What you think the docs should say:

For Altair :

c = alt.Chart(df).mark_circle().encode(x='a', y='b', size='c', color='c', tooltip=['a', 'b', 'c'])

For vega-lite :

st.vega_lite_chart(df, {
    "mark": {"type": "circle", "tooltip": True},
    'encoding': {
        'x': {'field': 'a', 'type': 'quantitative'},
        'y': {'field': 'b', 'type': 'quantitative'},
        'size': {'field': 'c', 'type': 'quantitative'},
        'color': {'field': 'c', 'type': 'quantitative'}
    },
})

Also

So I could find charts.vega_lite_chart.py source file for a Streamlit vega-lite but there's no tooltip so I guess that's not the one which generated the embedded app. Could not find charts.altair_chart.py nor text.write4.py so I'm not sure which source file generated the app.