Tau. reads your data directly from Apple Health: there is nothing to enter manually. Grant Health access and your metrics appear in the Data tab. Nothing is copied outside the Health app: each value is read on your device, only when it is needed.
Choose a period: Day, Week, Month, Year or All. You can go back to earlier periods using the arrows below. Metrics are listed under collapsible categories. Tap a chart to open it full-size, and tap the star to pin a metric to your Favorites. The switch at the top of the list lets you hide metrics with no data.
Four tabs: Evolution compares the current period with the previous one, Rhythm looks for a pattern that repeats from one week or one year to the next, Correlation pairs two metrics, Variability looks at how stable a metric is. Correlation and Variability require tapping Compute; the other two display on their own. The ⓘ button next to the page title explains, tab by tab, what each result means and how it is calculated.
The AI tab lets you ask questions about your data: the model queries the app for the values and calculations it needs, then answers. Just above the input box, three chips control the conversation: the AI provider, the thinking level (model) and the tone. Each selector has its own ⓘ explanation page, detailing what the setting changes.
The AI provider is the company whose model you are using: Gemini, Mistral, ChatGPT or Claude. Tau. has no server: the chat runs on your own API key, created with the AI provider, and requests go directly from your device. What Tau. sends, what it never sends, and what a key costs are detailed in “Choose an AI”, from the AI provider selector.
The ⋯ button top right opens “How it works”, the conversation history, and lets you disconnect your API key. The pencil button starts a new chat: it permanently deletes the current conversation for the selected tone and AI provider.
The Export tab lets you export two types of files. Select the metrics first, then a period: all data, a year, a month, a week or a day. The CSV is a file meant for data analysis, while the PDF is an easy-to-read summary report.
In Settings › Reminders, you can receive a daily, weekly or monthly notification, and choose which metrics it covers. Tapping the notification opens a summary of the period: the tracked metrics, their average and their change. These reminders are local; nothing is sent anywhere.
Preferences groups theme, font, language and date format. The same page handles privacy: access to Apple Health (which opens in the system Settings), whether reproductive health is included in what the AI can read, and the consent given to each AI provider, revocable at any time. On iOS 26, the Medications row opens the system window where you choose, medication by medication, what Tau. can read.
Days with no recording are treated as absent: no calculation in the app counts them as zero.
If you wear an Apple Watch, its measurements (sleep stages, HRV, wrist temperature…) flow into Apple Health automatically and appear in Tau., no separate Watch app needed.