Slipstream replays any Formula 1 session from the OpenF1 API, with a track map, timing tower and race control, and can follow a live session through a small relay. On top of that are the views I wanted as a fan: a train-timetable (Marey) chart of the whole race, an estimate of each car’s battery deployment, and forecasts of which battles are about to come alive.

Most of the work is in the data. The free API allows 30 requests a minute, so ingestion is rate-limited and cached, and a race is packed from about 250 MB of raw JSON into about 5 MB. The feed has stalls and physically impossible positions. Those get dropped, gaps are filled from sector timing, and anything estimated is labelled as a guess.

103 tests keep it honest, including one that replays the 2026 Italian Grand Prix and checks the result against the official classification.