Bindu - A2A Protocol Compliant AI Agent Framework

The simplest possible x402-paywalled agent. Same echo handler as the basic echo agent, but the message/send method is gated: the server returns HTTP 402 with payment requirements until the caller pays the configured amount ($0.0001 USDC in the example below) on Base Sepolia.

Code

Create echo_agent_behind_paywall.py with the code below, or save it directly from your editor.

"""Echo Testing Agent

A minimal Bindu agent for testing connectivity.
Echoes back user input to verify the system is working.

Features:
- Simple echo functionality
- No external dependencies
- Perfect for testing Bindu installation
- Lightweight and fast

Usage:
    python echo_simple_agent.py

Environment:
    No environment variables required
"""

from bindu.penguin.bindufy import bindufy


def handler(messages):
    """Handle incoming messages by echoing back the user's latest input.

    Args:
        messages: List of message dictionaries containing conversation history.

    Returns:
        List containing a single assistant message with the user's content.
    """
    # Reply with the user's latest input
    return [{"role": "assistant", "content": messages[-1]["content"]}]


config = {
    "author": "gaurikasethi88@gmail.com",
    "name": "echo_agent",
    "description": "A basic echo agent for quick testing.",
    "deployment": {
        "url": "http://localhost:3773",
        "expose": True,
        "cors_origins": ["http://localhost:5173"]
    },
    "skills": ["skills/question-answering", "skills/pdf-processing"],
    "execution_cost": {
    "amount": "$0.0001",
    "token": "USDC",
    "network": "base-sepolia",
    "pay_to_address": "0x2654bb8B272f117c514aAc3d4032B1795366BA5d",
    "protected_methods": [
      "message/send"
    ]
  },
}

bindufy(config, handler)

# if you want to use tunnel to expose your agent to the internet, use the following command
#bindufy(config, handler, launch=True)

How It Works

Handler

Same echo logic as the basic echo agent — returns the user’s latest message back
No model call, no external dependencies

x402 paywall block

execution_cost in the config declares the price and chain
amount: $0.0001 charged per request
token: USDC
network: base-sepolia (testnet — use the Circle faucet for test USDC)
pay_to_address: receiving wallet for the payment
protected_methods: list of A2A methods that require payment; here only message/send

The 402 response cycle

Caller sends message/send with no payment header
Server returns HTTP 402 Payment Required with x402 paymentRequirements describing the price, network, token, and payTo address
Caller signs an x402 payment (EIP-3009 transfer authorization on Base Sepolia) and resends the request with the X-PAYMENT header
Server verifies the signed payment, executes the handler, and returns the JSON-RPC result

Testing it

Fund a Base Sepolia wallet with test USDC from the Circle USDC faucet
Use an x402-aware client to handle the 402 → sign → retry loop automatically
tasks/get is not in protected_methods, so it remains free

Dependencies

uv init
uv add bindu

Environment Setup

No environment variables required for the server. The caller needs a funded Base Sepolia wallet with test USDC.

Run

uv run echo_agent_behind_paywall.py

Example API Calls

Message Send Request (no payment)

{
  "jsonrpc": "2.0",
  "method": "message/send",
  "params": {
    "message": {
      "role": "user",
      "kind": "message",
      "messageId": "9f11c870-5616-49ad-b187-d93cbb100001",
      "contextId": "9f11c870-5616-49ad-b187-d93cbb100002",
      "taskId": "9f11c870-5616-49ad-b187-d93cbb100003",
      "parts": [
        {
          "kind": "text",
          "text": "Repeat after me: hello paywall"
        }
      ]
    },
    "configuration": {
      "acceptedOutputModes": ["application/json"]
    }
  },
  "id": "9f11c870-5616-49ad-b187-d93cbb100003"
}

402 Payment Required Response

{
  "x402Version": 1,
  "error": "X-PAYMENT header is required",
  "accepts": [
    {
      "scheme": "exact",
      "network": "base-sepolia",
      "maxAmountRequired": "100",
      "resource": "http://localhost:3773/",
      "description": "Payment required for message/send",
      "mimeType": "application/json",
      "payTo": "0x2654bb8B272f117c514aAc3d4032B1795366BA5d",
      "maxTimeoutSeconds": 60,
      "asset": "0x036CbD53842c5426634e7929541eC2318f3dCF7e",
      "extra": {
        "name": "USDC",
        "version": "2"
      }
    }
  ]
}

Message Send Request (with X-PAYMENT header)

POST / HTTP/1.1
Host: localhost:3773
Content-Type: application/json
X-PAYMENT: <base64-encoded-x402-payment-payload>

{
  "jsonrpc": "2.0",
  "method": "message/send",
  "params": {
    "message": {
      "role": "user",
      "kind": "message",
      "messageId": "9f11c870-5616-49ad-b187-d93cbb100001",
      "contextId": "9f11c870-5616-49ad-b187-d93cbb100002",
      "taskId": "9f11c870-5616-49ad-b187-d93cbb100003",
      "parts": [
        {
          "kind": "text",
          "text": "Repeat after me: hello paywall"
        }
      ]
    },
    "configuration": {
      "acceptedOutputModes": ["application/json"]
    }
  },
  "id": "9f11c870-5616-49ad-b187-d93cbb100003"
}

Successful Response (after payment)

{
  "jsonrpc": "2.0",
  "id": "9f11c870-5616-49ad-b187-d93cbb100003",
  "result": {
    "id": "9f11c870-5616-49ad-b187-d93cbb100003",
    "status": { "state": "completed" },
    "artifacts": [
      {
        "parts": [
          { "kind": "text", "text": "Repeat after me: hello paywall" }
        ]
      }
    ]
  }
}

Task get Request

{
  "jsonrpc": "2.0",
  "method": "tasks/get",
  "params": {
    "taskId": "9f11c870-5616-49ad-b187-d93cbb100003"
  },
  "id": "9f11c870-5616-49ad-b187-d93cbb100004"
}

Frontend Setup

# Clone the Bindu repository
git clone https://github.com/GetBindu/Bindu

# Navigate to frontend directory
cd frontend

# Install dependencies
npm install

# Start frontend development server
npm run dev

Open http://localhost:5173 and try to chat with the echo paywall agent.

Beginner

Specialized

Advanced

1.12 Echo Agent Behind Paywall

Code

How It Works

Dependencies

Environment Setup

Run

Example API Calls

Frontend Setup

​Code

​How It Works

​Dependencies

​Environment Setup

​Run

​Example API Calls

​Frontend Setup

Code

How It Works

Dependencies

Environment Setup

Run

Example API Calls

Frontend Setup