Sign Endpoint

Sign messages and transactions without broadcasting them to the network.

Endpoint

POST /agent/sign

Overview

The sign endpoint allows you to cryptographically sign:

• Plain text messages — Standard Ethereum message signing (personal_sign)
• Typed data — EIP-712 structured data signing (eth_signTypedData_v4)
• Transactions — Sign a transaction without submitting it (eth_signTransaction)

This is a synchronous endpoint that returns immediately with the signature.

Request

Headers

Header	Value	Required
Content-Type	application/json	Yes
X-API-Key	Your API key	Yes

Body

The request body varies based on the signature type.

personal_sign

Sign a plain text message:

{
  "signatureType": "personal_sign",
  "message": "Hello, Bankr!"
}

Field	Type	Description	Required
signatureType	string	Must be "personal_sign"	Yes
message	string	The message to sign	Yes

eth_signTypedData_v4

Sign EIP-712 structured data:

{
  "signatureType": "eth_signTypedData_v4",
  "typedData": {
    "domain": {
      "name": "MyApp",
      "version": "1",
      "chainId": 8453,
      "verifyingContract": "0x..."
    },
    "types": {
      "Permit": [
        { "name": "owner", "type": "address" },
        { "name": "spender", "type": "address" },
        { "name": "value", "type": "uint256" },
        { "name": "nonce", "type": "uint256" },
        { "name": "deadline", "type": "uint256" }
      ]
    },
    "primaryType": "Permit",
    "message": {
      "owner": "0x...",
      "spender": "0x...",
      "value": "1000000",
      "nonce": "0",
      "deadline": "1707158800"
    }
  }
}

Field	Type	Description	Required
signatureType	string	Must be "eth_signTypedData_v4"	Yes
typedData	object	EIP-712 typed data structure	Yes
typedData.domain	object	Domain separator (name, version, chainId, verifyingContract)	Yes
typedData.types	object	Type definitions for the message	Yes
typedData.primaryType	string	The primary type being signed	Yes
typedData.message	object	The actual data to sign	Yes

eth_signTransaction

Sign a transaction without broadcasting:

{
  "signatureType": "eth_signTransaction",
  "transaction": {
    "to": "0x...",
    "chainId": 8453,
    "value": "1000000000000000000",
    "data": "0x..."
  }
}

Field	Type	Description	Required
signatureType	string	Must be "eth_signTransaction"	Yes
transaction.to	string	Destination address	Yes
transaction.chainId	number	Chain ID	Yes
transaction.value	string	Value in wei	No
transaction.data	string	Calldata (hex)	No
transaction.gas	string	Gas limit	No
transaction.gasPrice	string	Legacy gas price	No
transaction.maxFeePerGas	string	EIP-1559 max fee	No
transaction.maxPriorityFeePerGas	string	EIP-1559 priority fee	No
transaction.nonce	number	Transaction nonce	No

Response

Success (200 OK)

{
  "success": true,
  "signature": "0x...",
  "signer": "0x...",
  "signatureType": "personal_sign"
}

Field	Type	Description
success	boolean	true if signing succeeded
signature	string	The hex-encoded signature
signer	string	Address that produced the signature
signatureType	string	The signature type used

Error Responses

Invalid Request (400)

{
  "error": "Invalid request",
  "message": "signatureType is required"
}

Missing Field (400)

{
  "error": "Invalid request",
  "message": "message is required for personal_sign"
}

Signing Failed (400)

{
  "success": false,
  "error": "Signing failed",
  "signer": "0x...",
  "signatureType": "personal_sign"
}

Authentication Required (401)

{
  "error": "Authentication required",
  "message": "Valid API key with associated wallet required"
}

Agent Access Not Enabled (403)

{
  "error": "Agent API access not enabled",
  "message": "Enable agent access for your API key at bankr.bot/api"
}

Read-Only API Key (403)

{
  "error": "Read-only API key",
  "message": "This API key has read-only access and cannot sign messages or transactions. Update your API key permissions at https://bankr.bot/api"
}

note

This is a write operation. If your key has read-only mode enabled, disable it at bankr.bot/api or use a different key. See Access Control for details.

Examples

Sign a Message

curl -X POST https://api.bankr.bot/agent/sign \
  -H "Content-Type: application/json" \
  -H "X-API-Key: your_api_key_here" \
  -d '{
    "signatureType": "personal_sign",
    "message": "Sign in to MyApp at 2025-01-26T10:00:00Z"
  }'

Sign a Permit (EIP-2612)

curl -X POST https://api.bankr.bot/agent/sign \
  -H "Content-Type: application/json" \
  -H "X-API-Key: your_api_key_here" \
  -d '{
    "signatureType": "eth_signTypedData_v4",
    "typedData": {
      "domain": {
        "name": "USD Coin",
        "version": "2",
        "chainId": 8453,
        "verifyingContract": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913"
      },
      "types": {
        "Permit": [
          { "name": "owner", "type": "address" },
          { "name": "spender", "type": "address" },
          { "name": "value", "type": "uint256" },
          { "name": "nonce", "type": "uint256" },
          { "name": "deadline", "type": "uint256" }
        ]
      },
      "primaryType": "Permit",
      "message": {
        "owner": "0xYourAddress",
        "spender": "0xSpenderAddress",
        "value": "1000000",
        "nonce": "0",
        "deadline": "1735689600"
      }
    }
  }'

Sign a Transaction

curl -X POST https://api.bankr.bot/agent/sign \
  -H "Content-Type: application/json" \
  -H "X-API-Key: your_api_key_here" \
  -d '{
    "signatureType": "eth_signTransaction",
    "transaction": {
      "to": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
      "chainId": 8453,
      "value": "0",
      "data": "0xa9059cbb000000000000000000000000recipient0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000f4240"
    }
  }'

Use Cases

Authentication

Sign messages to prove wallet ownership for login flows:

{
  "signatureType": "personal_sign",
  "message": "Sign in to MyApp\n\nNonce: abc123\nTimestamp: 2025-01-26T10:00:00Z"
}

Gasless Approvals (Permits)

Sign EIP-2612 permits to approve token spending without gas:

{
  "signatureType": "eth_signTypedData_v4",
  "typedData": { ... }
}

Offline Transaction Signing

Sign transactions for later broadcast or multi-sig workflows:

{
  "signatureType": "eth_signTransaction",
  "transaction": { ... }
}

Verifying Signatures

personal_sign

Use viem or ethers to recover the signer:

import { recoverMessageAddress } from 'viem';

const signer = await recoverMessageAddress({
  message: "Hello, Bankr!",
  signature: "0x..."
});

eth_signTypedData_v4

Verify typed data signatures:

import { verifyTypedData } from 'viem';

const isValid = await verifyTypedData({
  address: "0x...",
  domain: { ... },
  types: { ... },
  primaryType: "Permit",
  message: { ... },
  signature: "0x..."
});

Next Steps

• Submit Endpoint — Submit signed transactions
• Transaction Types — Supported transaction formats