Dancode-188/synckit: 🔄 A powerful, type-safe sync engine for building real-time collaborative applications. Local-first, CRDT-based, with zero-config offline support.

synckit is one production ready sync engine Which makes it trivial to build local-first applications.

“Add sync.document() Get real-time sync automatically on your app.”

Problem: Building a sink from scratch takes months. Existing solutions are complex (Yjs), expensive (Firebase), or don’t work offline (Supabase).

Solution: SyncKit provides you with production-ready sync in 3 lines of code.

const sync = new SyncKit()
await sync.init()
const doc = sync.document<Todo>('todo-123')
await doc.update(Advanced features)
// ✨ Works offline, syncs automatically, resolves conflicts

Real-time collaboration with offline flexibility: See tasks instantly synced across tabs, even when offline. The example app demonstrates SyncKit’s offline-first capabilities combined with smart browser storage to create a seamless collaborative experience.

True offline-first architecture—not just caching. Your app works perfectly on planes, trains, tunnels and coffee shops with spotty WiFi.

~59 kb gzipped (10KB SDK + 49KB WASM) – Full WASM-based sync engine with TypeScript SDK.

Current Features (v0.1.0):

• ✅ Offline-First Sync (LWW)
• ✅ Real-time collaboration
• ✅ Network protocol support
• ✅ IndexedDB persistence
• ✅ Cross-tab sync (see example)

Coming in v0.2.0:

• 🚧 Text CRDT (character-level editing)
• 🚧 Counters, Sets (distributed data structures)

Size-critical apps? Use the Lite variant (~45 KB gzipped: 1.5KB SDK + 44KB WASM, local only)

Competitive Bundle Size: Larger than Yjs (~19KB pure JS), smaller than Automerge (~60-78KB).

Open source and self-hosted. No vendor lock-in, no surprise $2,000/month bills, complete data sovereignty.

• <1ms local operation (~5-20μs single field update)
• <100ms sync latency (10-50ms p95)
• ~59KB bundle (10KB SDK + 49KB WASM), ~45KB Lite option
• Total sub-200KB with React

• Zero data loss with automatic conflict resolution (last-write-wins)
• Formal validation with TLA+ (3 bugs found and fixed)
• 700+ comprehensive tests (unit, integration, chaos, load) in TypeScript and Rust

TL;DR:

• vs firebase: No vendor lock-in, real offline, predictable costs
• vs SupaBase: Really works offline (their #1 issue for 4+ years)
• vs YJS: WASM-based, simple API for structured data for multi-language server support
• vs automerge: Small bundle, fast performance, production ready

View detailed migration guides →

npm install @synckit-js/sdk

import { SyncKit } from '@synckit-js/sdk'
import { SyncProvider, useSyncDocument } from '@synckit-js/sdk/react'

// Initialize (works offline-only, no server needed!)
const sync = new SyncKit()
await sync.init()

function App() {
  return (
    <SyncProvider synckit={sync}>
      <TodoApp />
    </SyncProvider>
  )
}

function TodoApp() {
  const [todo, { update }] = useSyncDocument<Todo>('todo-1')

  if (!todo || !todo.text) return <div>Loading...</div>

  return (
    <div>
      <input
        type="checkbox"
        checked={todo.completed}
        onChange={(e) => update({ completed: e.target.checked })}
      />
      <span>{todo.text}</span>
    </div>
  )
}

That’s it! Now your app:

• ✅ Works 100% offline
• ✅ Syncs automatically across tabs
• ✅ Data is persisted in IndexedDB
• ✅ Resolves disputes automatically

bundle: SyncKit (~59 KB gzipped) + React (~130 KB) = ~189 KB total

Size-important? import { SyncKit } from '@synckit-js/sdk/lite' (~45 KB gzipped, local only)

Full Tutorial (5 mins) →

• 🔄 Real-time sync – WebSocket-based instant sync across devices
• 📴 Offline-First – Works perfectly with zero connectivity
• 🗄️ Local persistence – IndexedDB storage, unlimited capacity
• 🔀Conflict Resolution – Automatic Last-Write-Win (LWW) merge
• Fast operation – <1ms local updates, <100ms sync latency
• 📦 Compact Bundle – ~59KB gzipped (10KB SDK + 49KB WASM)
• 🔐safe – JWT authentication, RBAC permissions

• ⚛️ React Hook , useSyncDocument, useSyncField, SyncProvider
• 🌐 TypeScript Server – ban + hono reference implementation
• 📦Multi-version – Default (~59KB gzipped) or Lite (~45KB gzipped) builds

• ✍️ TEXT CRDT – Collaborative text editing (character-level sync)
• 🔢 counter – Conflict-free salary increase/decrease
• 📋 Sets and Lists – set overview-extract to archive
• 🎨 Framework Adapter – View Composables, Svelte Stores
• 🌐 Multi-language server – Python, Go, Rust implementations

graph TD
    A[Your Application
React/Vue/Svelte] --> B[SyncKit SDK
TypeScript]

    B -->|Simple API| B1[document, text, counter]
    B -->|Framework adapters| B2[React/Vue/Svelte hooks]
    B -->|Offline queue| B3[Storage adapters]

    B --> C[Rust Core Engine
WASM + Native]

    C -->|80% of use cases| C1[LWW Sync]
    C -->|Collaborative editing| C2[Text CRDTs]
    C -->|Advanced features| C3[Custom CRDTs
counters, sets]

    C --> D[IndexedDB Storage
Your local source of truth]

    D -.->|Optional| E[SyncKit Server
TypeScript/Python/Go/Rust]

    E -->|Real-time sync| E1[WebSocket]
    E -->|Persistence| E2[PostgreSQL/MongoDB]
    E -->|Security| E3[JWT auth + RBAC]

    style A fill:#e1f5ff,stroke:#333,stroke-width:2px,color:#1a1a1a
    style B fill:#fff4e1,stroke:#333,stroke-width:2px,color:#1a1a1a
    style C fill:#ffe1e1,stroke:#333,stroke-width:2px,color:#1a1a1a
    style D fill:#e1ffe1,stroke:#333,stroke-width:2px,color:#1a1a1a
    style E fill:#f0e1ff,stroke:#333,stroke-width:2px,color:#1a1a1a

Detailed Architecture Document →

Browse all documents →

Perfect for: Task apps, CRM, project management, note apps (80% of apps)

// Initialize once
const sync = new SyncKit()
await sync.init()

// Use anywhere
const doc = sync.document<Project>('project-123')
await doc.update({ status: 'completed' })
// Conflicts resolved automatically with Last-Write-Wins

Perfect for: Associate Editor, Documentation, Notes

// Note: Text CRDT API is planned for v0.2.0
const text = sync.text('document-456')
await text.insert(0, 'Hello ')
text.subscribe(content => editor.setValue(content))
// Character-level sync, conflict-free convergence

Perfect for: Whiteboard, design tools, specialized apps

// Note: Counter API is planned for v0.2.0
const counter = sync.counter('likes-789')
await counter.increment()
// Conflict-free counter (additions never conflict)

• @synckit-js/sdk – Core SDK (TypeScript) + WASM Engine
• @synckit-js/sdk/react – React hooks and components (exported from the SDK)
• @synckit-js/sdk/lite – Light version (local only, 45KB gzipped)

• @synckit-js/server – BUN+HONO Reference Server (Production Ready)

current version: v0.1.0
Production Ready: Core Sync Engine, React Hooks, TypeScript Server ✅

• core corrosion engine – LWW sync engine with CRDT foundation
• WASM compilation – 59KB gzipped (45KB lite), optimized performance
• typescript sdk – Document API, IndexedDB storage, offline queue
• cross-tab sync – Server-mediated sync with operation buffering for multi-tab sync
• feedback integration , useSyncDocument, useSyncField, SyncProvider hook
• typescript server – WebSocket sync server with bun + hono
• example application – Todo app, collaborative editor, project management demo
• documentation – Comprehensive guide and API reference
• manufacturing system – Full toolchain with benchmarks and CI

• text crdt – Collaborative text editing (useText hook) for character-level sync
• counter crdt – distributed counter (useCounter Hook) for conflict-free salary increases
• BroadcastChannel Cross-Tab – Direct client-to-client sync without server (offline multi-tab)
• framework adapter – View Composables (@synckit-js/sdk/vue), svelte stores (@synckit-js/sdk/svelte,
• multi-language server – Python, Go, Rust server implementations (TypeScript complete)
• advanced storage – OPFS (Origin Private File System), SQLite Adapter
• conflict ui – Visual conflict resolution interface for complex merge scenarios

Complete Roadmap →

We welcome contributions from the community!

Ways to contribute:

• bug reports – open an issue
• documentation – Improve guides, fix typos
• tests – Add test coverage
• server – Implement Python/Go/Rust Server
• features – Propose new features in discussions

Contribute Guide →

Need enterprise support?

• managed hosting – We host SyncKit servers for you
• priority support – 24/7 support, SLA guarantee
• monitoring and analysis – Dashboard, Alerts, Insights
• Training and Consulting – Onboarding, Architecture Review

contact: danbitengo@gmail.com

Yjs:                ~19 KB ████
SyncKit (lite):     ~45 KB █████████
SyncKit (default):  ~59 KB ████████████
Automerge:       ~60-78 KB ████████████████
Firebase:          ~150 KB ████████████████████████████████

Local update:       <1 ms  ████
Cross-tab sync:     <1 ms  ████
Network sync:    10-50 ms  ████████
Firebase (cold):  2-30 s   ████████████████████████████████

SyncKit:       3 MB  ████
Yjs:           8 MB  █████████
Automerge:   180 MB  ████████████████████████████████████████

Detailed benchmark →

Created with inspiration from:

• Yajas – YATA algorithm and performance optimization
• automerge – CRDT theory and formal verification
• linear – Practical approach to sync
• figma – Custom Sync Architecture Pattern
• rxdb – local-first database pattern

Special thanks to the local-first community for driving this movement forward.

MIT License – see License for details.

Copyright (c) 2025 Daniel Bitengo