walcast

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walcastPostgres change data capture for Node

A hand-written pgoutput decoder speaking the streaming replication protocol directly — an async iterator with explicit acks, and a plugin engine when you want a daemon.

Quickstart (library)
Quickstart (daemon)
Why walcast

Zero plugins to start

import { Walcast } from "walcast" and for-await your database changes. Your code is the sink — no daemon, no broker, no config file.

Honest delivery guarantees

At-least-once delivery with deterministic, LSN-derived event ids — exactly-once processing via consumer idempotency. Exactly-once into Kafka via transactional checkpoints. Nothing claimed that cannot hold.

Everything that transports is a plugin

The core ships zero sinks, like @babel/core ships zero transforms. Webhook, SSE, Kafka, and gRPC sinks are separate packages; yours is a ~50-line default export.

A real replication client

Speaks START_REPLICATION and pgoutput at the byte level, tracks LSNs as bigints, backpressures Postgres instead of dropping events, and only advances the slot past acknowledged work.

Operable by design

A tiny daemon with a bearer-token admin API and dashboard, per-sink durable checkpoints in your own database, pause/resume, and slot-lag visibility.

Typed events from your Prisma schema

@walcast/typegen-prisma generates self-contained row types that match what pgoutput actually delivers — no runtime imports.

The whole zero-plugin experience ​

ts
import { Walcast } from 'walcast'

const tr = new Walcast({ connection: process.env.DATABASE_URL! })
await tr.setup() // create publication + slot, idempotent

for await (const event of tr.changes()) {
  console.log(event.op, event.table, event.after)
  tr.ack(event) // the slot only advances past what you ack
}

Released under the MIT License.