# nanobook
[](https://github.com/ricardofrantz/nanobook/actions/workflows/ci.yml)
[](https://crates.io/crates/nanobook)
[](https://docs.rs/nanobook)
[](LICENSE)
**n*10⁻⁹** — A deterministic, nanosecond-precision limit order book and matching engine for testing trading algorithms.
## What Is This?
A **simulated stock exchange** that processes orders exactly like a real exchange — with proper price-time priority, partial fills, and cancellations.
### Who Should Use This?
| **Quant developer** | Backtesting trading strategies with realistic market microstructure |
| **Algo trader** | Testing order execution logic (slippage, queue position, fill rates) |
| **Student** | Learning how exchanges actually work under the hood |
| **Rust developer** | Reference implementation of a financial data structure |
### Why This Library?
- **Deterministic** — Same inputs always produce same outputs (essential for reproducible backtests)
- **Fast** — 8M+ orders/sec single-threaded, sub-microsecond latency
- **Complete** — GTC/IOC/FOK, partial fills, modify, cancel, L1/L2/L3 snapshots
- **Multi-symbol** — `MultiExchange` for independent per-symbol order books
- **Portfolio engine** — Position tracking, cost modeling, rebalancing, financial metrics (Sharpe, Sortino, max drawdown)
- **Simple** — Single-threaded, in-process, minimal dependencies
## See It In Action
```bash
cargo run --example demo # Interactive walkthrough with explanations
cargo run --example demo_quick # Quick non-interactive demo
```
```
Building order book...
SELL 100 @ $50.25 (Alice) ASK $50.50 150 shares
SELL 150 @ $50.50 (Bob) ASK $50.25 100 shares
BUY 100 @ $50.00 (Carol) ---- spread: $0.25 ----
BUY 200 @ $49.75 (Dan) BID $50.00 100 shares
BID $49.75 200 shares
Incoming: BUY 120 @ $50.25 (Eve) - CROSSES SPREAD!
Trades: 100 shares @ $50.25 (Alice filled completely)
Filled: 100, Resting: 20 (Eve's remainder rests on book)
Incoming: MARKET BUY 200 (Frank) - SWEEPS THE BOOK!
Trades: 150 shares @ $50.50 (Bob filled completely)
Unfilled: 50 (no more liquidity!)
```
The interactive demo explains price-time priority, partial fills, IOC/FOK, and order cancellation.
## Features
- **Order types**: Limit, Market, Cancel, Modify
- **Time-in-force**: GTC, IOC, FOK
- **Price-time priority**: FIFO matching at each price level
- **Nanosecond timestamps**: Monotonic counter (not system clock)
- **Deterministic**: Same inputs → same outputs (essential for backtesting)
- **Fast**: 8M+ orders/second single-threaded (see Performance)
- **Book snapshots**: L1 (BBO), L2 (depth), L3 (full book), imbalance, weighted mid
- **Event replay**: Complete audit trail for deterministic replay
- **Portfolio**: Position tracking, VWAP entry, cost model, Sharpe/Sortino/drawdown metrics
- **Multi-symbol**: Independent order books per symbol via `MultiExchange`
- **Parallel sweeps**: Rayon-based parameter grid search (optional feature)
## Quick Example
```rust
use nanobook::{Exchange, Side, Price, TimeInForce};
fn main() {
let mut exchange = Exchange::new();
// Alice sells 100 shares at $50.00
let alice = exchange.submit_limit(Side::Sell, Price(50_00), 100, TimeInForce::GTC);
// Bob sells 100 shares at $51.00
let bob = exchange.submit_limit(Side::Sell, Price(51_00), 100, TimeInForce::GTC);
// Charlie buys 150 shares at $51.00 — crosses the book!
let result = exchange.submit_limit(Side::Buy, Price(51_00), 150, TimeInForce::GTC);
// Two trades execute:
// 1. Charlie buys 100 from Alice at $50.00 (best price)
// 2. Charlie buys 50 from Bob at $51.00
assert_eq!(result.trades.len(), 2);
assert_eq!(result.trades[0].price, Price(50_00));
assert_eq!(result.trades[0].quantity, 100);
assert_eq!(result.trades[1].price, Price(51_00));
assert_eq!(result.trades[1].quantity, 50);
}
```
## Installation
Add to `Cargo.toml`:
```toml
[dependencies]
nanobook = "0.3"
```
Or build from source:
```bash
git clone https://github.com/ricardofrantz/nanobook
cd nanobook
cargo build --release
cargo test
cargo bench
```
## API Overview
### Core Types
```rust
/// Price in smallest units (e.g., cents). Price(10050) = $100.50
#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct Price(pub i64);
/// Order side
pub enum Side { Buy, Sell }
/// Time-in-force: how long an order stays active
pub enum TimeInForce {
GTC, // Good-til-cancelled: rests on book until filled or cancelled
IOC, // Immediate-or-cancel: fill what you can, cancel the rest
FOK, // Fill-or-kill: fill entirely or cancel entirely
}
/// Order status
pub enum OrderStatus {
New, // Accepted, resting on book
PartiallyFilled, // Some quantity filled, rest on book
Filled, // Fully executed
Cancelled, // Removed by user or TIF
}
```
### Exchange Operations
```rust
let mut exchange = Exchange::new();
// Submit limit order (returns order ID + any immediate trades)
let result = exchange.submit_limit(Side::Buy, Price(100_00), 100, TimeInForce::GTC);
println!("Order ID: {:?}, Trades: {}", result.order_id, result.trades.len());
// Submit market order (always IOC semantics)
let result = exchange.submit_market(Side::Sell, 50);
// Cancel an order
let cancel_result = exchange.cancel(order_id);
// Modify an order (cancel + replace, loses time priority)
let modify_result = exchange.modify(order_id, Price(101_00), 200);
// Get order status
if let Some(order) = exchange.get_order(order_id) {
println!("Remaining: {}", order.remaining_quantity);
}
// Book snapshots
let (best_bid, best_ask) = exchange.best_bid_ask(); // L1
let depth = exchange.depth(10); // L2: top 10 levels
let full = exchange.full_book(); // L3: everything
```
### Result Types
```rust
pub struct SubmitResult {
pub order_id: OrderId,
pub status: OrderStatus,
pub trades: Vec<Trade>,
}
pub struct Trade {
pub id: TradeId,
pub price: Price,
pub quantity: Quantity,
pub aggressor_order_id: OrderId,
pub passive_order_id: OrderId,
pub aggressor_side: Side,
pub timestamp: Timestamp,
}
```
## How It Works
### Order Book Structure
```
BIDS (sorted high→low) ASKS (sorted low→high)
$100.00: [O1]→[O2]→[O3] $100.50: [O7]→[O8]
$99.50: [O4]→[O5] $101.00: [O9]
$99.00: [O6] $102.00: [O10]→[O11]
↑ Best Bid ↑ Best Ask
```
- **BTreeMap<Price, Level>** for sorted price levels
- **VecDeque<Order>** for FIFO queue at each level
- **HashMap<OrderId, OrderRef>** for O(1) lookup/cancel
- **Cached best_price** for O(1) BBO access
### Matching Algorithm
1. Incoming order checks opposite side of book
2. If prices cross (buy ≥ best ask, or sell ≤ best bid), match
3. Fill at resting order's price (price improvement for aggressor)
4. Continue until no more crosses or order fully filled
5. Remaining quantity: rests (GTC), cancels (IOC/Market), or entire order cancels (FOK)
### Time-in-Force Behavior
| GTC | Yes | Yes (remainder) |
| IOC | Yes | No (remainder cancelled) |
| FOK | No | No (all-or-nothing) |
### Determinism
- No randomness anywhere
- Timestamps from monotonic counter, not system clock
- Same order sequence always produces same trades
- Event log enables exact replay
## Performance
### Benchmarks
Measured on AMD Ryzen / Intel Core (single-threaded):
| Submit (no match) | **120 ns** | 8.3M ops/sec | O(log P) |
| Submit (with match) | ~200 ns | 5M ops/sec | O(log P + M) |
| BBO query | **1 ns** | 1B ops/sec | O(1) |
| Cancel | 660 ns† | 1.5M ops/sec | O(N) |
| L2 snapshot (10 levels) | ~500 ns | 2M ops/sec | O(D) |
Where P = price levels, M = orders matched, N = orders at price level, D = depth.
†Cancel is O(N) in orders at that price level. See "Future Optimizations" below.
```bash
cargo bench
```
### Optimizations Applied
1. **FxHash** — Non-cryptographic hash for OrderId lookups (+25% vs std HashMap)
2. **Cached BBO** — Best bid/ask cached for O(1) access
3. **Optional event logging** — Disable for max throughput:
```bash
# With event logging (default) - enables replay
cargo build --release
# Without event logging - maximum performance
cargo build --release --no-default-features
```
### Where Time Goes (Submit, No Match)
```
submit_limit() ~120 ns breakdown:
├── FxHashMap insert ~30 ns order storage
├── BTreeMap insert ~30 ns price level (O(log P))
├── VecDeque push ~5 ns FIFO queue
├── Event recording ~10 ns (optional, for replay)
└── Overhead ~45 ns struct creation, etc.
```
### Future Optimizations
| **O(1) cancel** | 10x for deep levels | High | Intrusive linked list or tombstones |
| **Array-indexed levels** | -30 ns | Medium | Requires bounded price range |
| **Slab allocator** | -10 ns | Medium | More complex memory management |
**O(1) Cancel**: Currently cancel scans the VecDeque to find the order. For true O(1):
- Tombstone approach: mark cancelled, skip during matching
- Intrusive doubly-linked list with HashMap<OrderId, NodePtr>
These add complexity. Current O(N) cancel is fine unless you have thousands of orders at a single price level (rare in practice).
## Use Cases
### Strategy Backtesting
```rust
for event in historical_events {
let result = exchange.apply(&event);
strategy.on_result(&result);
strategy.on_book_update(exchange.best_bid_ask());
}
```
### Market Impact Analysis
```rust
let (bid_before, _) = exchange.best_bid_ask();
let result = exchange.submit_market(Side::Buy, 10_000);
let (bid_after, _) = exchange.best_bid_ask();
let slippage = bid_after.unwrap().0 - bid_before.unwrap().0;
```
### Queue Position Testing
```rust
// Who's first in line at $100?
let competitor = exchange.submit_limit(Side::Buy, Price(100_00), 1000, TimeInForce::GTC);
let mine = exchange.submit_limit(Side::Buy, Price(100_00), 1000, TimeInForce::GTC);
// Sell comes in — who gets filled?
exchange.submit_limit(Side::Sell, Price(100_00), 500, TimeInForce::GTC);
// Competitor was first, gets filled first
let comp_order = exchange.get_order(competitor.order_id).unwrap();
let my_order = exchange.get_order(mine.order_id).unwrap();
assert_eq!(comp_order.filled_quantity, 500);
assert_eq!(my_order.filled_quantity, 0);
```
### IOC for Aggressive Execution
```rust
// Take liquidity without resting an order
let result = exchange.submit_limit(Side::Buy, Price(100_50), 1000, TimeInForce::IOC);
// Fills what's available at ≤$100.50, remainder cancelled
println!("Filled: {}, Cancelled: {}",
result.trades.iter().map(|t| t.quantity).sum::<u64>(),
exchange.get_order(result.order_id).map(|o| o.remaining_quantity).unwrap_or(0)
);
```
## Comparison with Other Rust LOBs
| **nanobook** (this) | **8M ops/sec** | Single | Limit, Market, GTC/IOC/FOK | **Yes** | Backtesting, education |
| [limitbook](https://lib.rs/crates/limitbook) | 3-5M ops/sec | Single | Limit, Market | No | General purpose |
| [lobster](https://lib.rs/crates/lobster) | ~300K ops/sec | Single | Limit, Market | No | Simple matching |
| [OrderBook-rs](https://github.com/joaquinbejar/OrderBook-rs) | 200K ops/sec | **Multi** | Many (iceberg, peg, etc.) | No | Production HFT |
**When to use what:**
- **This library**: You need deterministic replay for backtesting, or you're learning how exchanges work
- **limitbook**: General-purpose LOB without replay requirements
- **OrderBook-rs**: Production systems needing thread-safety and complex order types
## Feature Flags
| `event-log` | Yes | Event recording for deterministic replay |
| `serde` | No | Serialize/deserialize all public types |
| `persistence` | No | File-based event sourcing (JSON Lines) |
| `portfolio` | No | Portfolio engine, position tracking, metrics |
| `parallel` | No | Rayon-based parallel parameter sweeps |
## Limitations
This is an **educational/testing tool**, not a production exchange:
- **No networking**: In-process only
- **No compliance**: Self-trade prevention, circuit breakers
- **No complex orders**: Iceberg, pegged, trailing stops
See SPECS.md for the complete specification.
## License
MIT
## Contributing
Issues and PRs welcome. See SPECS.md for the technical specification.
### Recording a Demo GIF
To create an animated GIF of the demo (for docs, presentations, etc.):
```bash
# Using vhs (recommended): https://github.com/charmbracelet/vhs
vhs examples/demo.tape
# Using asciinema + agg:
asciinema rec demo.cast -c "cargo run --example demo_quick"
agg demo.cast demo.gif
```