One-time licenses instead of per-call fees: shipping a paid MCP server with x402

Description and use

The author implemented an MCP server with a one‑time license instead of per‑call fees, using x402 and Base mainnet, simplifying payment for tools used a few times a day.

Problem

Per-call billing for MCP servers creates a subscription‑like experience for tools used a few times a day, making micropayments cumbersome.

Outcome

The MCP server successfully implements a one‑time license model, reducing payment friction for users and demonstrating that x402 can support license‑based billing.

Workflow

• 1. Client requests /api/comprar and receives a 402 response with payment details.
• 2. Client pays via an x402‑capable facilitator and retries with an X-PAYMENT header.
• 3. Server verifies payment, mints a license token, and returns it in a JSON response.
• 4. Client includes the x-license header on subsequent MCP calls.
• 5. Server validates the license hash stored in KV and enforces a 200‑call/month limit per license.

Evidence

Everyone writing about paid MCP servers right now is charging per call.

Source

a one-time 5 USDC payment on Base mainnet.

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The license travels as a plain header on every MCP call: x-license: ct_...

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Store only the hash. The KV namespace never sees the license token, only sha256(token).

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Cap heavy buyers in the product, not in the contract. 200 calls per month per license.

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