Self-hosted real-time CRDT sync server.
Open-source alternative to Liveblocks and PartyKit — no vendor lock-in, no merge conflicts.

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What is Meridian?

Meridian is a self-hosted server that lets multiple clients share state in real-time without conflicts. You pick a CRDT type (counter, set, register, presence), apply operations from any client, and every client converges to the same value automatically — no locks, no last-write-wins bugs.

Quick start

# Start the server
MERIDIAN_SIGNING_KEY=$(openssl rand -hex 32) docker compose up -d

# Issue a token
curl -X POST http://localhost:3000/v1/namespaces/my-room/tokens \
  -H "Authorization: Bearer $ADMIN_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"client_id": 1, "ttl_ms": 3600000}'

Usage

React

import { MeridianProvider, useGCounter, usePresence } from "meridian-react";
import { Schema } from "effect";

function App() {
  return (
    <MeridianProvider url="ws://localhost:3000" token={token}>
      <Room />
    </MeridianProvider>
  );
}

const CursorSchema = Schema.Struct({ x: Schema.Number, y: Schema.Number });

function Room() {
  const { value, increment } = useGCounter("gc:views");
  const { online } = usePresence("pr:cursors", {
    schema: CursorSchema,
    data: { x: mouseX, y: mouseY },
    ttlMs: 5_000,
  });

  return <p>{value} views · {online.length} online</p>;
}

TypeScript (framework-agnostic)

import { MeridianClient } from "meridian-sdk";
import { Effect } from "effect";

const client = await Effect.runPromise(
  MeridianClient.create({ url: "http://localhost:3000", namespace: "my-room", token })
);

const views = client.gcounter("gc:views");
views.increment(1);
views.onChange(v => console.log("views:", v.total));

client.close();

CRDT types

Type	Use case	Example key
GCounter	Page views, likes	gc:views
PNCounter	Inventory, votes	pn:stock
ORSet	Shopping cart, tags	or:cart
LwwRegister	User profile, config	lw:title
Presence	Who's online, cursors	pr:room

Packages

Package	Description
meridian-sdk	TypeScript SDK — Effect-based, msgpack, fully typed
meridian-react	React hooks — useGCounter, usePresence, etc.

Features

• Real-time sync over WebSocket with automatic reconnection
• 5 CRDT types covering the most common collaborative patterns
• Scoped permissions — token-level read/write access with glob patterns (allowed:*)
• Rate limiting — 100 req/s per token, sliding window
• Webhooks — POST to your backend on every op, HMAC-SHA256 signed
• Prometheus metrics — ops counter, active WS connections, WAL entries (GET /metrics)
• WAL compaction — automatic background truncation
• History API — audit log per CRDT (GET /v1/namespaces/:ns/crdts/:id/history)
• 124 tests — unit, property-based, and integration

Configuration

Variable	Default	Description
MERIDIAN_BIND	0.0.0.0:3000	TCP bind address
MERIDIAN_DATA_DIR	./data	sled storage path
MERIDIAN_SIGNING_KEY	(random)	32-byte hex ed25519 seed
MERIDIAN_WEBHOOK_URL	(unset)	Webhook endpoint URL
MERIDIAN_WEBHOOK_SECRET	(unset)	HMAC-SHA256 signing secret

Stack

Server: Rust · tokio · axum · sled · ed25519 · proptest

SDK: TypeScript · Effect 3 · msgpackr · Bun