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Overview

The Agentic API is the x402-paid surface for Brickken agentic methods. It covers ERC-8004 agent identity, reputation, and agent-owned ERC-20 token operations on Base mainnet and Base Sepolia. Every agentic operation is a two-step flow:
  1. Prepare the unsigned transaction — free, no x402 payment required.
  2. Send the operation — the x402 USDC payment is charged here, and only here.
There are two execution modes for the send step:
  • brickken-relayed (recommended). You do not sign the blockchain transaction. You pay the x402 charge and Brickken’s relayer signs, pays native gas, and broadcasts the operation on your behalf. No EOA, no native gas, no on-chain signing on your side.
  • client-signed. You sign the prepared blockchain transaction with your own private key and submit the signed payload. Use this when you want to retain full self-custody of signing.
Never send a private key to the Brickken API. In brickken-relayed mode you only sign the x402 payment authorization. In client-signed mode, blockchain signing belongs in your client, the Brickken CLI, or an MCP session you control.

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Base URLs

EnvironmentBase URL
Sandboxhttps://api.sandbox.brickken.com
Productionhttps://api.brickken.com

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Networks

The Agentic API runs on Base, with Base Sepolia for tests. The x402 payment rail is operation-aligned: you pay on the same chain the operation runs on.
NetworkchainId (decimal)HexUse
Base mainnet84530x2105Production
Base Sepolia845320x14a34Testing
Ethereum Sepolia111551110xaa36a7Legacy testing

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Authentication Flow

For x402, omit x-api-key.
  1. Prepare (free). Call a semantic facade such as POST /x402/agent/register, or POST /prepare-transactions with an eligible method. For relayed execution, pass executionMode: "brickken-relayed". The response returns txId, transactions, and an x402Requirements quote of the upcoming send price. No payment is taken at this step.
  2. Send. Call POST /send-transactions. The API responds 402 Payment Required with a PAYMENT-REQUIRED header describing the exact chain, asset, transfer method, amount, recipient, and timeout.
  3. Sign the x402 payment locally with the payer’s private key, and retry the send with X-PAYMENT.
  4. Brickken verifies the payment, then (in brickken-relayed mode) signs and broadcasts the operation. The settlement is returned in the PAYMENT-RESPONSE header.
X-PAYMENT: BASE64_ENCODED_X402_PAYMENT_PAYLOAD
Always read the chain, asset, transfer method, amount, recipient, and timeout from PAYMENT-REQUIRED; do not hardcode them client-side. On Base Sepolia the payment rail uses EIP-3009; on Base mainnet it follows the advertised token’s transfer method.
In brickken-relayed mode, x402 payment is mandatory — API keys are not accepted on the send step. The payment is reserved when you pay and only settled after the operation confirms on-chain. If the operation reverts or its authorization expires before confirmation, the reservation is released.

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Base Sepolia Testing

Use chainId: "84532" (eip155:84532). The Base Sepolia x402 payment asset is Circle USDC: 
0x036CbD53842c5426634e7929541eC2318f3dCF7e
It has 6 decimals and uses the EIP-3009 transfer method (EIP-712 name USDC, version 2, authorization window 300s). Fund the payer with the exact asset advertised by PAYMENT-REQUIRED before signing. The Base Sepolia ERC-8004 registries are:
  • Identity: 0x8004A818BFB912233c491871b3d84c89A494BD9e
  • Reputation: 0x8004B663056A597Dffe9eCcC1965A193B7388713

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Discovery

GET /.well-known/x402
GET /openapi.json
Production (https://api.brickken.com) is the public x402scan target. Sandbox exposes the same discovery routes for QA.

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Prepare and Send

The semantic /x402/... routes prepare unsigned transactions for free. They do not submit transactions on-chain by themselves. Prepare with executionMode: "brickken-relayed" and omit signerAddress — Brickken supplies its relayer as the signer. 
curl --request POST 'https://api.sandbox.brickken.com/x402/agent/register' \
  --header 'Content-Type: application/json' \
  --data '{
    "chainId": "84532",
    "executionMode": "brickken-relayed",
    "name": "Research Agent",
    "description": "Autonomous research agent",
    "image": "https://example.com/agent.png",
    "services": [
      {
        "name": "A2A",
        "endpoint": "https://agent.example/.well-known/agent-card.json",
        "version": "0.3.0"
      }
    ],
    "aiModelName": "Research Model",
    "aiModelProvider": "OpenAI",
    "x402Support": true,
    "active": true
  }'
image is required for agentRegister and must be a publicly reachable HTTPS logo URL. Do not use local paths or omit the field.
The prepare response returns a single txId, exactly one transaction { to, data, value }, and x402Requirements. Submit those to send-transactions and complete the x402 payment; Brickken signs and broadcasts: 
curl --request POST 'https://api.sandbox.brickken.com/send-transactions' \
  --header 'Content-Type: application/json' \
  --header 'X-PAYMENT: BASE64_ENCODED_X402_PAYMENT_PAYLOAD' \
  --data '{
    "txId": "0xPreparedTransactionId",
    "transactions": [
      { "to": "0xRegistry", "data": "0x...", "value": "0x0" }
    ]
  }'

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Client-signed

Prepare with your own signerAddress, sign the returned transaction locally, then send the signed payload: 
curl --request POST 'https://api.sandbox.brickken.com/send-transactions' \
  --header 'Content-Type: application/json' \
  --header 'X-PAYMENT: BASE64_ENCODED_X402_PAYMENT_PAYLOAD' \
  --data '{
    "txId": "0xPreparedTransactionId",
    "signedTransactions": ["0xSignedRawTransaction"]
  }'
send-transactions x402 batches must contain only x402-eligible prepared transactions, and all transactions in the batch must be on the same chain. A brickken-relayed send carries a single txId and exactly one transaction.

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Polling

For relayed operations, poll status with GET /get-transaction-status by txId or operation hash — no API key is required for brickken-relayed transactions. A response of status: "pending" means the operation was broadcast but not yet confirmed; do not pay or resubmit the same txId again. Brickken’s reconciliation settles after confirmation or releases the payment on revert or authorization expiry.

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Endpoint Groups

Facade requests use the same body fields as the matching backend method, except method is optional and ignored because the path fixes it.

Agent Identity

Register, maintain, and transfer ownership of ERC-8004 agent identities.

Reputation

Give, revoke, and respond to ERC-8004 feedback.

Agent Tokens

Create and operate agent-owned ERC-20 tokens.

Pricing

Review free prepare and per-operation send prices.
Advanced clients can also call POST /prepare-transactions directly and pass method explicitly. newTokenizedAgent remains a legacy alias for agent registration, but it is not published in x402scan discovery.

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Common Fields

FieldTypeRequiredDescription
chainIdstringYesTarget chain ID. Use 8453 for Base mainnet or 84532 for Base Sepolia. Decimal and hex values are accepted.
methodstringYes for /prepare-transactions; no for /x402/... facadesOne of the eligible method names. Facades derive it from the path.
executionModestringNobrickken-relayed (Brickken signs and broadcasts) or client-signed (default).
signerAddressstringConditionalRequired in client-signed mode. Omit in brickken-relayed mode — Brickken sets its relayer as the signer.
gasLimitstring or numberNoOptional explicit gas limit (client-signed).
noncenumberNoOptional explicit nonce when managing nonces manually (client-signed).

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Response Shape

The prepare response includes txId, transactions, and optional info. For agentRegister, save info.agentUuid for later set-uri, set-metadata, and transfer-ownership calls.
x402 payments and on-chain transactions are non-refundable. Confirm chain, signer/recipient, token address, and expected USDC price before paying. See Pricing for the published mainnet table.