> ## Documentation Index
> Fetch the complete documentation index at: https://docs.dokrypt.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Cross-Chain Bridge

> Simulate cross-chain transfers and message relaying between local networks.

## Overview

Dokrypt's bridge simulator lets you test cross-chain workflows locally. It simulates token transfers between local chains by modifying balances directly — no actual cross-chain messaging protocol is involved.

This is useful for:

* Testing multi-chain dApps
* Simulating L1↔L2 bridges
* Testing cross-chain token transfers
* Developing bridge aggregators

## Setup

To use the bridge, your `dokrypt.yaml` needs multiple chains:

```yaml theme={null}
version: "1"
name: multi-chain-app

chains:
  ethereum:
    engine: anvil
    chain_id: 31337
    block_time: "2s"
  polygon:
    engine: anvil
    chain_id: 137
    block_time: "2s"

services:
  bridge:
    type: mock-bridge
    chains: [ethereum, polygon]
```

Start the environment:

```bash theme={null}
dokrypt up
```

## Sending Transfers

Simulate a cross-chain transfer:

```bash theme={null}
# Bridge 100 ETH from ethereum to polygon
dokrypt bridge send ethereum polygon 100
```

With options:

```bash theme={null}
# Specify sender
dokrypt bridge send ethereum polygon 50.5 --from 0x1234...abcd

# Bridge tokens
dokrypt bridge send polygon ethereum 1000 --token USDC
```

### How It Works

1. Resolves RPC endpoints for both chains
2. Sends a transaction to the bridge contract (`0x...B12D`) on the source chain
3. Mines a block on the source chain
4. Reads the recipient's current balance on the destination chain
5. Adds the bridged amount to the balance on the destination chain

## Bridge Status

Check the status of bridge queues:

```bash theme={null}
dokrypt bridge status
```

```
Bridge          Chains              Relay Delay   Confirmations   Queue
eth-polygon     ethereum → polygon  30s           12              0 pending
```

## Relay Messages

Force relay pending bridge messages by mining confirmation blocks:

```bash theme={null}
dokrypt bridge relay
dokrypt bridge relay --blocks 5
```

This mines blocks on each chain and triggers the bridge service relay endpoint.

## Bridge Configuration

View the full bridge configuration:

```bash theme={null}
dokrypt bridge config
```

### Configuration in dokrypt.yaml

```yaml theme={null}
services:
  bridge:
    type: mock-bridge
    chains: [ethereum, polygon]
    confirmation_blocks: 12
    relay_delay: 30s
```

| Field                 | Type       | Default  | Description         |
| --------------------- | ---------- | -------- | ------------------- |
| `chains`              | `string[]` | required | Connected chains    |
| `confirmation_blocks` | `int`      | `12`     | Blocks before relay |
| `relay_delay`         | `duration` | `30s`    | Delay before relay  |

## Multi-Bridge Setup

You can configure multiple bridges for complex multi-chain scenarios:

```yaml theme={null}
chains:
  ethereum:
    engine: anvil
    chain_id: 31337
  polygon:
    engine: anvil
    chain_id: 137
  arbitrum:
    engine: anvil
    chain_id: 42161

services:
  eth-polygon-bridge:
    type: mock-bridge
    chains: [ethereum, polygon]
    confirmation_blocks: 12
  eth-arbitrum-bridge:
    type: mock-bridge
    chains: [ethereum, arbitrum]
    confirmation_blocks: 6
```

```bash theme={null}
dokrypt bridge send ethereum polygon 100
dokrypt bridge send ethereum arbitrum 50
```

<Note>
  The bridge simulator directly modifies destination chain balances. It does not deploy or interact with actual bridge smart contracts. For testing real bridge protocol implementations, deploy the bridge contracts as part of your project.
</Note>