Accord

Accord is a composable domain modeling library for TypeScript. Simplifying DDD for the rest of us.

You define business rules, record what happened, and describe what should happen next. Business failures are plain tagged values. Every operation returns [value, null] or [null, error]. Effect is optional.

import { aggregate, event, integer, model, ok, refine, wire } from '@marcelsud/accord'

const Cents = refine(integer, (amount) => amount > 0, 'positive cents')
const Deposited = event('Deposited', { amount: Cents, balance: integer })

class Account extends aggregate('Account', { balance: 0 }) {
  deposit(amount: number) {
    const event = Deposited({ amount, balance: this.state.balance + amount })

    this.state.balance = event.balance
    this.emit(event)

    return ok({ balance: this.state.balance })
  }
}

const Bank = model('Bank', { aggregates: { account: Account } })
const bank = wire(Bank)

const [receipt, error] = await bank.account.deposit('account-123', 100)
if (error !== null) throw error
console.log(receipt.reply) // { balance: 100 }

That's it. wire() gives you a typed client. Each call loads the stored state, runs your method on an isolated instance, and commits state and events together.

Quick Start

Accord isn't on npm yet. Build a tarball from the repository and install it:

git clone https://github.com/marcelsud/accord.git
cd accord
npm ci --ignore-scripts
npm pack

Then follow Getting Started.

Features

• Small API: aggregate, event, rejection, view, policy, projection, model, wire. That's most of it.
• Typed tuples: no hidden throws. Rejections are values, and match() checks you handled every one.
• Runtime schemas: integer, string, refine, union, and friends validate events, rejections, and inputs at runtime.
• Read your own writes: view.get(key, { atLeast: receipt }) catches a view up to your command.
• Durable when you need it: @marcelsud/accord/sqlite persists state, history, views, and checkpoints with Node.js's built-in SQLite.
• Zero runtime dependencies: Effect is an optional peer, used only by @marcelsud/accord/effect.
• Testable: story() runs a scenario against a fresh in-memory runtime and returns a tuple.

Entry points

Import	What you get
@marcelsud/accord	The core: schemas, results, definitions, runtime, HTTP transport, stories
@marcelsud/accord/sqlite	The sqlite() durable store (Node.js 24 built-in node:sqlite)
@marcelsud/accord/effect	effectify() for Effect v4.1.2+

Version 0.1

This is the first version. The runtime is in-process, workflows are memory-only, and no npm release has been published yet. See Limits of v0.1.

Next

• Getting Started: install and run your first aggregate.
• Motivation: why Accord looks the way it does.
• Examples: bank, notifications, durable bank, and a CRM with migrations.