Metri

Context

Metri is a workout tracker for people who need their training data fast, private and always available — including in a gym with no signal. The app runs entirely on the device and is fully usable without signing in. The code is open source under the MIT license, and the beta APK (v1.7.0, Android open beta) is distributed from metri.info/download.

Architecture

The central decision is that the database drives the UI: there is no Zustand, no Redux, no TanStack Query. SQLite (with Drizzle ORM) is the single source of truth, and its useLiveQuery reacts directly to writes, which removes a whole class of state-synchronization bugs. MMKV covers synchronous hot-path reads (theme, units, session) without replacing the relational store. Drizzle Kit generates and applies SQL migrations automatically on each launch.

Automatic premium sync does push→pull with delta sync, tombstones and exponential backoff; the wire-format contract with the web app (metri.info) is maintained by hand across both repositories.

Stack

• Expo SDK 56 + React Native 0.85 with strict TypeScript.
• Expo Router (file-based routing with typed routes).
• expo-sqlite + Drizzle ORM as the offline-first source of truth; MMKV for key-value reads.
• NativeWind v4 with design tokens; Reanimated v4 for animation.
• Better Auth Expo for accounts; Sentry for error tracking.

Features

• A workout-session engine and an editor for programmes, routines and days.
• 16 calculators and a knowledge base with a custom Markdown renderer.
• A headless Android home-screen widget that reads SQLite without opening the UI.
• Local notifications with Android channels and a rest timer.
• Progress photos kept fully on-device; EN/ES i18n and light/dark/system themes.
• OTA updates through EAS and release engineering across 4 GitHub Actions workflows.

Technical challenges

• Designing a pure, synchronous formula engine safe to call on every keystroke without UI flicker.
• Delta sync with tombstones and exponential backoff against a backend whose contract is maintained by hand.
• An Android widget that queries the database directly, with no UI process.

Outcome

An app in open beta (public repository) that demonstrates an uncommon offline-first architecture: a reactive UI driven by the database, delta sync designed end to end, and automated release engineering.