Freemium for AI Agents: Free vs Paid Tiers via HTTP 402 in an MCP Server

AgentBadge implemented a freemium paywall for AI agents in its MCP server using HTTP 402 and the x402 payment scheme, allowing one free request per minute before returning a 402 response with a machine-readable invoice. Agents pay 5 USDC on the Arc Testnet via an EIP-3009 transfer signature to receive a 30-day ServicePass, with the server verifying the on-chain receipt and rejecting replayed transaction hashes with a tx_replayed error. The approach removes the need for API keys, signup, email, or a card, letting an agent see the price, sign a transfer, and gain access in seconds.

Freemium for AI Agents: Free vs Paid Tiers via HTTP 402 in an MCP Server How do you sell freemium to an agent with no card and no checkout form? HTTP 402 + x402: a programmable paywall where the agent pays on-chain in seconds. Freemium for AI agents works via HTTP 402: one free request per minute, then a 402 response carrying an x402 payment challenge — the agent pays on-chain and gets a 30-day ServicePass, no account or checkout needed. Every SaaS has a free tier and a paid tier. But how do you sell the paid tier when the customer is not a person but a program? An agent has no card, cannot fill a checkout form, cannot type a CVV. We solved it with HTTP 402 Payment Required — a status code that waited three decades for its moment. It is not an error. It is an invoice. Every request passes three doors: a live ServicePass means instant real-time; otherwise the free bucket allows one request per minute a snapshot ; otherwise the server answers 402 with an invoice. One USDC transaction 5 USDC on Arc , an on-chain receipt check — and the agent holds a 30-day ServicePass. How the gate works Every request to the tracker passes three checks: 1. Already paid? If the agent holds a live ServicePass a 30-day access token — data flows immediately. 2. Free allowance? One request per minute is free. A snapshot, not a stream. 3. Neither? The server answers 402 and attaches an invoice to the response: what, to whom, how much. Inside the invoice The 402 response is not just text. The PAYMENT-REQUIRED header carries a machine-readable payment description: { "x402Version": 2, "accepts": { "scheme": "eip3009-client-broadcast", "network": "eip155:5042002", "asset": "USDC", "amount": "5000000", "payTo": "0xcdd2...699d", "maxTimeoutSeconds": 345600 } } The agent reads it like a price list: the payment scheme EIP-3009 — a standardized transfer signature , the network Arc Testnet , the asset USDC , the amount 5 USDC — the six zeros are decimals, the amount is in base units , the recipient, and the invoice expiry 4 days . Why not API keys and billing portals An API key needs signup, an email, a card, invoices — a human in the loop. 402 + x402 is a programmable paywall: the agent sees the price → signs a transfer → pays → gets access. The whole cycle takes seconds. For a machine, this is the native way to buy things. One payment pays once After paying, the agent retries the request with the transaction hash attached. The server checks the blockchain — not a claimed signature, but the real receipt from a block — and opens access. The same hash cannot be presented twice: the server atomically claims it, and a second attempt gets tx replayed . Even ten parallel requests with the same hash — exactly one gets through. Next: the payment itself on Arc — and why gas there is paid in USDC. Links - Agent guide endpoints, limits, examples : agentbadge.xyz/bstock-guide https://agentbadge.xyz/bstock-guide - All articles in the series: agentbadge.xyz/blog https://agentbadge.xyz/blog - MCP endpoint: https://agentbadge.xyz/mcp/bstock/tools/get delta