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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.

Features

A chess clock made for blitz

  • Defaults to 5+3 Fischer timing: 5 minutes + 3 seconds per move
  • FIDE-compliant: initial time for 5+3 is 5:03, not 5:00
  • Privacy-friendly: no ads, no permissions

Fast and intuitive controls

  • Touching the screen switches to the next player
  • Horizontal and vertical dragging set the time and increment
  • Haptic feedback is enabled by setting the ringtone to vibrate
  • Back gestures pause and reset the clock

Robust time implementation

  • Uses the most precise time source available on the device
  • Clock implementation tested with 100% code coverage

Free and secure

  • Free software with reproducible builds
  • Meets Android 15 security requirements
  • Enables memory tagging on compatible devices

Install

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 but requires Obtainium to update automatically.

The app can be updated from a different source. For example, if the app was installed from F-Droid, it can be updated to a newer version from the Play Store.

Signing key certificate fingerprint 
6D 7F D2 71 5E D2 1C FF 64 08 6D C5 FC F8 82 0A 68 5A 79 3E BD 07 D9 72 16 3D 86 17 2B AB BA 75

To verify that an APK was signed with the developer's signing key, check that the above fingerprint is identical to the one output by apksigner:

apksigner verify --min-sdk-version 24 --print-certs blitz.apk
Code transparency key certificate fingerprint 
FA BD 43 3F C7 1A 5E 00 39 1B 0D 48 B1 2E 42 F6 33 3F 0E 18 EE C9 3A C0 81 74 C6 95 4F 13 B9 6F

To verify that the DEX files present in an APK were not modified by Google, create a ZIP archive of the APK and check that the above fingerprint is identical to the code transparency fingerprint output by bundletool:

bundletool check-transparency --mode=apk --apk-zip=blitz.apk.zip

About

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

Screenshots

 Screenshot of the initial view ​  Screenshot when time is over