Your entire backend in a single binary.
Real-time by default.

Cosmictron is a database that runs your application logic. Write reducers in Rust or TypeScript, deploy as a module, and get real-time subscriptions, auth, and security — no app server, no pub/sub layer, no glue code. One binary replaces your whole backend stack.

Try the Demo View on GitHub

Why Cosmictron

Incremental subscriptions

Only changed rows are recomputed, even across joins and aggregations. O(delta) instead of O(N) — powered by DBSP circuits.

Security you can't forget

Declarative row-level security that works with subscriptions and joins. Policies are SQL predicates, automatically injected into every query.

No vendor lock-in

Self-hosted, truly open-source (MIT/Apache 2.0). Your data, your infrastructure, your terms.

Native TypeScript, not compiled WASM

V8 runtime with full npm ecosystem access. Write modules in TypeScript with the libraries you already know.

See It in Action

Define your tables and logic in Rust. Subscribe from TypeScript. That's it.

module.rs Server — Rust module

#[table(name = "messages", public)]
pub struct Message {
    #[primary_key] #[auto_inc]
    pub id: u64,
    pub sender: Identity,
    pub text: String,
    pub ts: Timestamp,
}

#[reducer]
fn send(ctx: &ReducerContext, text: String) {
    Message::insert(ctx.db, Message {
        id: 0, sender: ctx.sender,
        text, ts: ctx.timestamp,
    });
}

client.ts Client — TypeScript

import { Cosmictron } from "@cosmictron/sdk";

const db = new Cosmictron({
  host: "localhost:3000",
  module: "chat",
});

// Subscribe — only deltas are sent
db.subscribe("SELECT * FROM messages");

db.on("messages", (change) => {
  for (const msg of change.inserts) {
    console.log(`${msg.sender}: ${msg.text}`);
  }
});

db.call("send", { text: "Hello!" });

How It Compares

	Cosmictron	Firebase	Supabase	SpacetimeDB
Embedded business logic	WASM + V8	Cloud Functions (separate)	Edge Functions (separate)	WASM only
Real-time subscriptions	DBSP incremental	Yes (full re-eval)	Yes (row-level)	Yes (full re-eval for joins)
Incremental joins/aggs	Yes	No	No	No
Declarative RLS	Yes	No (Security Rules DSL)	Yes (Postgres RLS)	No
TypeScript modules	Native V8	Node.js (separate service)	Deno (separate service)	No (C# or Rust)
Self-hosted	Yes (MIT/Apache 2.0)	No	Yes	BSL 1.1

Your entire backend in a single binary. Real-time by default.