Sync that works offline.

A local-first sync engine for TypeScript, React, and Next.js. Every read is instant. Every write works offline. Every client converges.

Linear built a sync architecture that became the gold standard for local-first apps, but never open-sourced it. Strata Sync is an open-source implementation of that architecture, extended with Yjs CRDT collaboration, undo/redo, and pluggable adapters.

• Instant reads: Local IndexedDB replica. No spinners, no round-trips.
• Offline support: Writes queue offline and sync when you reconnect.
• Fine-grained reactivity: MobX observables. Only affected components re-render.
• Real-time collaboration: Multiple users edit the same document with Yjs.
• Undo and redo: Transaction-based history tracking.
• Modular: Swap storage, transport, or reactivity adapters.

Scaffold a full-stack app with the Claude Code skill:

npx skills add stratasync/stratasync

Or install the packages manually:

npm install @stratasync/core @stratasync/client @stratasync/react @stratasync/mobx @stratasync/storage-idb @stratasync/transport-graphql

import { ClientModel, Model, Property } from "@stratasync/core";

@ClientModel("Todo", { loadStrategy: "instant" })
class Todo extends Model {
  @Property() declare title: string;
  @Property() declare completed: boolean;
}

import { createSyncClient } from "@stratasync/client";
import { createMobXReactivity } from "@stratasync/mobx";
import { createIndexedDbStorage } from "@stratasync/storage-idb";
import { GraphQLTransportAdapter } from "@stratasync/transport-graphql";

const client = createSyncClient({
  storage: createIndexedDbStorage(),
  transport: new GraphQLTransportAdapter({
    endpoint: "/api/graphql",
    syncEndpoint: "/api/sync",
    wsEndpoint: "wss://api.example.com/sync/ws",
    auth: { getAccessToken: async () => "token" },
  }),
  reactivity: createMobXReactivity(),
});

import { observer } from "mobx-react-lite";
import { useQuery, useSyncClient } from "@stratasync/react";

const TodoList = observer(() => {
  const { data: todos } = useQuery("Todo", {
    where: (t) => !t.completed,
  });
  const { client } = useSyncClient();

  const addTodo = async () => {
    const todo = await client.create("Todo", {
      title: "New todo",
      completed: false,
    });
    todo.title = "Actually, a better title";
    await todo.save();
  };

  return (
    <ul>
      {todos.map((todo) => (
        <li key={todo.id}>{todo.title}</li>
      ))}
      <button onClick={addTodo}>Add</button>
    </ul>
  );
});

Full documentation at stratasync.dev/docs.

core | client | react | mobx | y-doc | next | storage-idb | transport-graphql | server

MIT