Using Zeitlog¶
Zeitlog is a free, browser-based sleep and circadian-rhythm tracker. It charts your sleep over time so circadian patterns — like the daily drift seen in Non-24 — are easy to see.
Importing data¶
Zeitlog can import sleep records directly from:
- Google Health API — the successor to the Fitbit Web API.
- Fitbit Web API — legacy; scheduled for deprecation in September 2026.
Both run entirely in your browser, so your health data is not sent to a server. Follow the setup steps shown in Zeitlog's import dialog.
No wearable?
You can also keep a diary by hand or import a spreadsheet — see Create a sleep diary and the software directory.
Reading the chart¶
Zeitlog plots each sleep episode against the time of day across many days:
- A rhythm entrained to 24 hours appears as roughly horizontal bands.
- A free-running rhythm (as in Non-24) appears as a diagonal that drifts across the chart.
See Sleeping patterns for help recognising what you're looking at.
Contributions welcome
Screenshots, worked examples, and tips for interpreting your own chart would make this page much more useful — add them.