OpenScore

One-liner

A scoring and scheduling engine for any sport, built on one contract: apply(state, action, ruleset) → {state, events}.

Why

Every sports app reinvents scoring logic, but scoring is fundamentally a pure function: given a state and an action, produce a new state and events. Extract that layer and the engine becomes reusable across sports and platforms.

Core Design

Action-sourced, not event-sourced. The engine is passive — it doesn’t track time, only reacts to actions. History is an action sequence, not an event log. Undo = replay from scratch minus the last action, not a reversal.

State bubbling: Point scored → recursively check win conditions upward. game_won → set_won → match_won, events bubble bottom-up.

Declarative rulesets: Win conditions, display formats, special behaviors are all config, not code. Same engine, different ruleset, different sport.

Supported Sports

9 sports, 18+ rulesets:

Sport	Rulesets
Tennis	standard, grand slam, no-ad
Badminton	standard, doubles
Basketball	NBA, FIBA, 3x3
Padel	standard, golden point
Pickleball	rally scoring, side-out
Table Tennis	standard, short
Volleyball	standard
Baseball	MLB
Softball	fastpitch

Cross-Language Conformance

The engine is implemented in 4 languages: Elixir (all 9 sports), JavaScript, Swift, and Kotlin. All implementations run the same JSON conformance test suite (609 cases) to guarantee identical behavior.

Three-Layer Architecture

Platform Layer — Phoenix API + WebSocket + Astro frontend + iOS (SwiftUI)
Schedule Layer — Tournament engine (knockout, double elimination, round robin, swiss, group knockout)
Match Layer   — Single-match scoring engine

The schedule engine handles winner_of / loser_of dependency resolution: match completed → resolve downstream brackets → emit match_ready when both sides are determined.

Realtime Sync

Phoenix Channels handle live scoring sync. Match Channel and Session Channel let multiple viewers watch the same match’s live score. The iOS app stays in sync via WebSocket.