Sign Messages

Sign EIP-712 typed data and plain messages with your Base Account using Base MCP

What it does

The sign tool requests a cryptographic signature from your Base Account. Like all write tools, it requires your approval at keys.coinbase.com.

Two signature types are supported:

Type	Standard	Use case
0x45	personal_sign (EIP-191)	Simple text messages, SIWE auth challenges
0x01	EIP-712 typed data	Structured data, permit signatures, protocol auth

What you can ask

Sign this message: "I agree to the terms of service"

Sign in to this app using my Base Account

Signing is usually invoked by protocols or integrations, not directly prompted by users. Your assistant will handle the signing flow when a service requests it.

How it works

1. Your assistant calls sign()

   Passes the message type and payload to Base MCP.

2. You receive an approval link

   Open keys.coinbase.com to review what you’re signing — the message content is shown in full.

3. You approve

   Confirm the signature in the approval UI.

4. Signature returned

   Your assistant polls get_request_status to retrieve the completed signature, then passes it to the requesting service.

Related guides

Execute contract calls

Batch multiple contract interactions into one approval.

Morpho plugin

Example of signing-in-the-flow with a DeFi protocol.