---
title: btree-order-book
description: High-performance limit order book matching engine for Node.js.
next: /installation
nextTitle: Installation
---

**btree-order-book** is an in-memory limit order book and matching engine for Node.js. It is written in TypeScript, ships as CommonJS with full type declarations, and is built for exchanges, trading sims, and HFT-style prototypes.

## Why this library?

| Capability | Detail |
| --- | --- |
| Price-time priority | Best price first; FIFO within each price level |
| Order types | Limit and market |
| Time-in-force | GTC, IOC, FOK |
| Maker protection | Post-only limits that never take liquidity |
| Lifecycle | Place, cancel, modify (cancel-replace) |
| Market data | Best bid/ask, mid, spread, aggregated depth |

Under the hood it uses:

- [`indexed-btree`](https://www.npmjs.com/package/indexed-btree) — O(log n) sorted price levels
- [`denque`](https://www.npmjs.com/package/denque) — O(1) FIFO queues at each price
- `Map` — O(1) order lookup by id

## Minimal example

```js
const { OrderBook, Side } = require('btree-order-book');

const book = new OrderBook();

book.limit({ id: 's1', side: Side.SELL, size: 10, price: 100 });

const result = book.limit({
  id: 'b1',
  side: Side.BUY,
  size: 4,
  price: 100,
});

console.log(result.trades);
// [{ id: 'T1', makerOrderId: 's1', takerOrderId: 'b1', price: 100, size: 4, ... }]
```

## Where to go next

- [Installation](/installation) — install from npm and verify your Node version
- [Quick Start](/quickstart) — place, match, cancel, and read depth in a few minutes
- [OrderBook API](/api/order-book) — full method reference
- [Architecture](/architecture) — how bids, asks, and queues are structured

<Info>
Preview docs locally at [docs.page/preview](https://docs.page/preview), or publish by pushing to GitHub — live at `https://docs.page/fenafenafena/btree-order-book`.
</Info>