x402 protocol specification v0.9 active

The HTTP 402 Payment Required Gateway for AI Agents

Deploy programmatic micro-billing, wallet spending boundaries, and user-authorized stablecoin settlement flows optimized specifically for machine-to-machine commerce.

402 PAYREQUIRED Headers

HTTP 402 Gate

Intercept AI agent queries, reply with standardized 402 headers defining dynamic stablecoin pricing.

POLICY CONTROL Rules

Wallet Permissions

Define precise spending caps, duration limits, and user-approved policies for complete budget protection.

STABLECOIN Settlement

Micro-Settlement

Execute fraction-of-a-cent payments instantly over low-cost blockchain layers with instant confirmation.

REPLAY SHIELD Audit Hash

Audit Ledger

Track off-chain signatures and proof-of-payment receipts safely with complete replay protection.

99.999%
Uptime SLA
< 15ms
Response Delay
1.2M+
Settle Requests/Sec
USDC / EURC
Supported Assets

The x402 Protocol Flow

How AI Agents request and settle digital assets seamlessly without human manual approvals.

m2m-payment-facilitator-handshake.log

1. Agent Request to Paywalled Resource

GET /v1/mcp/vector-search HTTP/1.1
Host: api.provider.com
X-Agent-Identity: "agent-llm-789"
Accept: application/json
            

2. Server Intercept with 402 Payment Required

HTTP/1.1 402 Payment Required
X-402-Price: 0.0005 USDC
X-402-Invoice: "inv-987cf2"
X-402-Facilitator: "https://pay.x402.org"
            

Enforcing Strict Wallet Permission Policies

We guarantee absolute protection against unauthorized draining by establishing cryptographic guardrails on every machine transaction.

🛡️

Dynamic Spending Caps

Establish strict thresholds (e.g., maximum 0.05 USDC per single execution) to block runaway recursive agent requests.

🔑

User-Approved Policies

Define temporal and domain bounds. Every signature requires explicit client pre-authorization policies.

📝

Proof-of-Payment Headers

Leverage deterministic signature hashes for replay-attack shielding, validating double-spend resistance on each API ping.

Developer Resources & Industry Insights

Latest updates on stablecoin micro-settlement, autonomous API monetization, and MCP tool developments.

UCard:Everything You Need to Know

UCard:Everything You Need to Know

Learn what UCard is how it works where you can use it what items may qualify and how x402 Agentic Payment helps reduce payment friction

Bridge Your APIs to the Agentic Economy

Start building in minutes. Integrate our B2B compliant payment protocol and unlock instant machine-to-machine monetization.

Download Protocol SDK