How AI agents pay with x402

x402 turns the standard HTTP 402 (Payment Required) status code into a machine-readable checkout in USDC (usually on Base, CAIP-2 eip155:8453). An AI agent needs no account, no human typing a card number, and no pre-issued API key: it reads the price from the 402 challenge, signs an authorization within its spend limits, and retries the same HTTP request.

The 4-step x402 HTTP 402 flow

1. 1Call the endpoint unpaid

   The agent makes a normal GET or POST request to the API route. Nothing is spent to discover the price.

2. 2Read the HTTP 402 challenge

   The server answers HTTP 402 with an accepts[] array in the JSON body (and base64 in the PAYMENT-REQUIRED header on x402 v2) stating the exact scheme, network (such as eip155:8453), token contract, atomic amount, and payTo address.

3. 3Sign an off-chain USDC transfer authorization

   If the price fits the agent wallet budget, the wallet signs an EIP-3009 transferWithAuthorization payload (no gas transaction broadcast by the agent itself) and sends it in the PAYMENT-SIGNATURE header (or X-PAYMENT on v1).

4. 4Verify, settle, and receive HTTP 200

   The server (or its x402 facilitator) verifies the signature, settles the USDC transfer on-chain, and returns the API response along with a PAYMENT-RESPONSE receipt header.

# Step 1: Agent sends a normal HTTP request with no API key
GET /api/v1/pro HTTP/2
Host: satbotly.com

# Step 2: Server returns HTTP 402 + x402 v2 payment requirements
HTTP/2 402
PAYMENT-REQUIRED: <base64 JSON>
{"x402Version":2,"accepts":[{"scheme":"exact","network":"eip155:8453","amount":"9000000","asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","payTo":"0xeDb324E75A7dD36846576b8D46d3b43D7Df4f0FA","maxTimeoutSeconds":300}]}

# Step 3: Agent wallet signs an EIP-3009 USDC authorization and retries
GET /api/v1/pro HTTP/2
PAYMENT-SIGNATURE: <base64 PaymentPayload>

# Step 4: Server verifies + settles via facilitator and returns HTTP 200
HTTP/2 200
PAYMENT-RESPONSE: <base64 settlement receipt>

You can inspect a live x402 v2 402 response right now without paying: curl -i -s https://satbotly.com/api/v1/pro. More IDE examples: /from-agent-ide.

Wallets and buyer tools that let an agent pay x402

54 wallets in our leaderboard list the x402 rail. Top 10 by verified agent-readiness score (out of 7):

• Agent402 · score 7 / 7 · MCP server with wallet/payment tools
• AbaPay · score 6 / 7 · MCP server with wallet/payment tools
• mcp · score 6 / 7 · MCP server with wallet/payment tools
• agentic-wallet-guardian-v3 · score 5 / 7 · MCP server with wallet/payment tools
• bolthub-sdk · score 5 / 7 · MCP server with wallet/payment tools
• leashd · score 5 / 7 · LLM purchase with ecash/Lightning
• lightning-enable-mcp · score 5 / 7 · MCP server with wallet/payment tools
• 402-mcp · score 4 / 7 · LLM purchase with ecash/Lightning
• agentwallet-mcp · score 4 / 7 · MCP server with wallet/payment tools
• Alby Account · score 4 / 7 · Wallet interface (NWC)

All 54 x402 wallets → · All 64 x402 MCP servers →

Cheapest 10 live x402 APIs (from unpaid probes)

Every endpoint below answered HTTP 402 to our unpaid probe. Prices are read straight from the x402 challenge:

• x402wrapper · $0.0001 (USDC (x402)) · x402-wrapper.onrender.com
• API Acre — Base block inspection · $0.0010 (USDC (x402)) · API Acre
• Agent402 hash (MPP) (x402) · $0.0010 (USDC (x402)) · Havok Holdings LLC
• Agent402 stock-quote (MPP) (x402) · $0.0010 (USDC (x402)) · Havok Holdings LLC
• AgentIndex can-pay (MPP) · $0.0010 (USDC (x402)) · AgentIndex
• Ankr Monad RPC (JSON-RPC call) · $0.0010 (USDC (x402)) · Ankr
• Base ERC-20 Allowance Check · $0.0010 (USDC (x402)) · base-onchain-tools
• Base Gas Oracle · $0.0010 (USDC (x402)) · market
• Brand Extractor — logos, colors and fonts (alias) · $0.0010 (USDC (x402)) · Brand Extractor
• Brand Extractor — website logos, colors & fonts · $0.0010 (USDC (x402)) · Brand Extractor

25 cheapest x402 APIs → · All 367 x402 APIs → · x402 vs L402 comparison →

Data as of 2026-10-24. How we check: /method.