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Blitz: Fischer Chess Clock

A minimalist Fischer chess clock for Android.

This app is free software. Its source code is available under the Apache License 2.0.


Fast and intuitive controls

  • Made for blitz: defaults to 5+3 Fischer timing (5 minutes + 3 seconds per move)
  • Fast: time and increment are set by horizontal and vertical dragging
  • Responsive: haptic feedback is enabled by setting the ringtone on vibrate
  • Intuitive: back gestures pause and reset the clock

Robust time implementation

  • Robust: tested with 100% code coverage
  • Precise: uses the most precise time source available on the device
  • FIDE-compliant: 5+3 Fischer timing starts at 5:03 (not 5:00)

Secure and privacy-friendly

  • Privacy-friendly: no ads, no permissions
  • Free: open source with reproducible builds
  • Secure: enforces Android 14 security improvements


The app can be installed from four different sources:

  1. F-Droid: built and signed by the developer and verified by F-Droid to correspond to the available source code.
  2. Accrescent: built and signed by the developer.
  3. Play Store: built and signed by Google who can modify the app to optimize its performance, security and/or size.
  4. GitHub: built and signed by the developer.

As the app is signed using the same private signing key on all sources, it can be updated using a different source to the one it was installed from. For example, an app installed from F-Droid can be updated to a newer version downloaded from the Play Store.

Public key certificate fingerprint


This is a native Android app for Android 5.0+. It is built with Jetpack Compose and implements:

  • Predictive back gestures (Android 14+)
  • Per-app language preferences (Android 13+)
  • Hardware memory tagging (Android 13+)
  • Support for right-to-left languages
  • Precise handling of orientation
  • Keyboard navigation

License: Apache-2.0 — Website — Issue Tracker — Source Code — Changelog — Privacy Policy


 Screenshot of the initial view ​  Screenshot when time is over