# How to Use Timeboost APIs with the Arbitrum MCP Server: A Complete Guide

> Learn how to use Timeboost APIs with the Arbitrum MCP Server to enable priority transaction processing via express lanes. This guide details the timeboost_sendExpressLaneTransaction RPC method.

- Repository: [Dewansh/arbitrum-mcp](https://github.com/dewanshparashar/arbitrum-mcp)
- Tags: how-to-guide
- Published: 2026-02-28

---

**Timeboost APIs enable priority transaction processing through express lanes, and the Arbitrum MCP Server exposes this functionality via the `timeboost_sendExpressLaneTransaction` RPC method that routes submissions directly to Nitro nodes.**

Timeboost express lanes are a specialized Arbitrum Nitro feature designed to accelerate transaction processing beyond standard L1-sequenced throughput. The `dewanshparashar/arbitrum-mcp` repository provides a Model Context Protocol (MCP) server implementation that wraps these Timeboost APIs, making express lane functionality accessible to AI agents and automated tooling through a standardized interface.

## What Are Timeboost APIs and Express Lanes?

Timeboost is an Arbitrum Nitro mechanism that creates **express lanes**—dedicated transaction pathways that bypass the standard sequencing queue. Transactions submitted through these lanes receive priority inclusion, reducing latency for time-sensitive operations.

The **Timeboost API** refers to the JSON-RPC method `timeboost_sendExpressLaneTransaction`, which allows authorized clients to submit transactions to these priority lanes. The Arbitrum MCP Server abstracts this low-level RPC into a higher-level tool that MCP-compatible clients can invoke.

## Architecture of Timeboost Integration in Arbitrum MCP Server

The integration follows a three-layer architecture: the MCP command dispatcher receives the request, delegates to the Nitro node client, and returns a standardized response.

### Command Dispatcher in src/index.ts

The MCP server registers the `timeboost_sendExpressLaneTransaction` tool in the command dispatcher located at [`src/index.ts`](https://github.com/dewanshparashar/arbitrum-mcp/blob/main/src/index.ts) (lines 684‑701). When an MCP client invokes this tool, the dispatcher:

1. Extracts the `rpcUrl` and `submission` parameters from the request.
2. Instantiates the `NitroNodeClient` with the resolved RPC endpoint.
3. Awaits the result and formats it into the MCP response schema.

### NitroNodeClient Implementation

The `NitroNodeClient` class in [`src/clients/nitro-node-client.ts`](https://github.com/dewanshparashar/arbitrum-mcp/blob/main/src/clients/nitro-node-client.ts) (lines 446‑464) implements the actual RPC wrapper. Its `sendExpressLaneTransaction` method constructs the JSON-RPC payload and forwards it to the Nitro node:

- The method internally calls `timeboost_sendExpressLaneTransaction` on the target node (implementation spans lines 448‑563).
- It returns a typed object `{ success: boolean; error?: string }` that the dispatcher wraps into the final MCP response.

This architecture ensures that any MCP-compatible client—whether Claude Desktop, Cline, or custom scripts—can invoke Timeboost functionality without managing raw RPC connections.

## How to Send Express Lane Transactions

You can interact with Timeboost APIs through three primary interfaces: the MCP CLI, an MCP client JSON payload, or direct programmatic access via the `NitroNodeClient` class.

### Using the MCP CLI

Invoke the tool directly from the command line, providing the RPC endpoint and the signed transaction payload:

```bash
timeboost_sendExpressLaneTransaction \
  --rpcUrl http://my-nitro-node:8547 \
  --submission '{"txData":"0x...","signature":"0x..."}'

```

*Parameters:*
- `--rpcUrl`: Optional if a default RPC is configured in the server environment; otherwise, the target Nitro node address.
- `--submission`: A JSON object containing `txData` (the raw transaction bytes) and `signature` (the authorizing signature), formatted according to the Nitro node specification.

The CLI routes the request through [`src/index.ts`](https://github.com/dewanshparashar/arbitrum-mcp/blob/main/src/index.ts) and returns a JSON response indicating success or failure.

### From an MCP Client (Claude Desktop)

When configuring an MCP client such as Claude Desktop, define the tool invocation in your client configuration or prompt:

```json
{
  "tool": "timeboost_sendExpressLaneTransaction",
  "args": {
    "rpcUrl": "http://my-nitro-node:8547",
    "submission": {
      "txData": "0x...",
      "signature": "0x..."
    }
  }
}

```

The MCP client sends this JSON-RPC request to the running Arbitrum MCP Server, which processes it via the `NitroNodeClient` and returns the standardized result.

### Programmatic Usage via NitroNodeClient

For Node.js applications extending the MCP server or requiring direct integration, import and instantiate the client:

```typescript
import { NitroNodeClient } from "./src/clients/nitro-node-client";

async function submitExpressLane() {
  const client = new NitroNodeClient("http://my-nitro-node:8547");
  
  const submission = {
    txData: "0x...",
    signature: "0x..."
  };
  
  const result = await client.sendExpressLaneTransaction(submission);
  console.log(result); 
  // Output: { success: true } or { success: false, error: "..." }
}

submitExpressLane();

```

This approach bypasses the MCP command dispatcher, reducing overhead when you do not need the full MCP protocol layer.

## Error Handling and Troubleshooting

Both the command dispatcher and `NitroNodeClient` normalize RPC errors into a consistent payload structure. When a submission fails—whether due to an unsupported endpoint, invalid signature, or network timeout—the response follows this format:

```json
{
  "content": [
    {
      "type": "text",
      "text": "{\"success\":false,\"error\":\"Express lane transaction not supported on this RPC endpoint: ...\"}"
    }
  ]
}

```

**Common failure modes:**
- **Unsupported endpoint**: The target Nitro node does not have Timeboost enabled. Verify that your `--rpcUrl` points to a node with express lane capabilities.
- **Malformed submission**: Ensure `txData` and `signature` are properly hex-encoded and match the Nitro node's expected schema.
- **Connection refused**: Confirm the RPC URL is reachable and the node is synchronized.

## Summary

- **Timeboost APIs** provide express lane functionality for priority transaction processing on Arbitrum Nitro nodes.
- The Arbitrum MCP Server exposes this via the `timeboost_sendExpressLaneTransaction` tool, implemented in [`src/index.ts`](https://github.com/dewanshparashar/arbitrum-mcp/blob/main/src/index.ts) (lines 684‑701) and [`src/clients/nitro-node-client.ts`](https://github.com/dewanshparashar/arbitrum-mcp/blob/main/src/clients/nitro-node-client.ts) (lines 446‑464).
- You can invoke the API through the MCP CLI, an MCP-compatible client configuration, or direct programmatic access via the `NitroNodeClient` class.
- All interfaces return a standardized `{ success: boolean, error?: string }` payload, with errors indicating whether the target node supports express lanes.

## Frequently Asked Questions

### What is the difference between regular and express lane transactions?

Regular transactions follow the standard Arbitrum sequencing pipeline, while express lane transactions submitted via **Timeboost APIs** bypass the standard queue for faster inclusion. The `timeboost_sendExpressLaneTransaction` method routes your transaction directly to the priority lane, reducing latency for time-critical operations.

### Which Nitro nodes support Timeboost APIs?

Not all public RPC endpoints enable express lane functionality. You must target a Nitro node that has explicitly activated the Timeboost feature. If you receive an error stating "Express lane transaction not supported on this RPC endpoint," verify with your node operator that Timeboost is enabled on the target instance.

### How do I format the submission payload for timeboost_sendExpressLaneTransaction?

The `submission` parameter must be a JSON object containing `txData` (the hex-encoded raw transaction bytes) and `signature` (the authorizing signature). For example: `{"txData":"0x...","signature":"0x..."}`. Ensure both fields are properly hex-prefixed and match the Nitro node's expected schema to avoid validation errors.

### Can I use Timeboost APIs without the MCP server wrapper?

Yes, you can call the underlying `timeboost_sendExpressLaneTransaction` JSON-RPC method directly on any compatible Nitro node. However, using the **Arbitrum MCP Server** provides standardized error handling, connection management, and MCP protocol compatibility, which simplifies integration with AI agents and automated tooling.