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

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 (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 (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:

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 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:

{
  "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:

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:

{
  "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 (lines 684‑701) and 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.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}