How do you monetize an MCP server with x402?
Return a machine-readable HTTP 402 challenge only when a paid MCP tool is invoked, let the caller approve those exact live terms, then execute the tool after payment verification. A 402 challenge is not a purchase. A signature is not settlement. Count the call as paid only when settlement succeeds and the requested result is delivered.
What is the ScriptMasterLabs x402 MCP endpoint?
The canonical public endpoint is https://mcp-x402.onrender.com/mcp. Current first-party authority is x402 v2 · Base mainnet · USDC.
What is the exact payment flow?
1. Agent connects to MCP and discovers tools. 2. Agent invokes a paid tool without a payment signature. 3. Server returns HTTP 402 + PAYMENT-REQUIRED. 4. Agent reads amount, network, asset, payTo and resource. 5. Caller policy decides whether to spend. 6. If approved, agent signs those exact terms and retries. 7. Server verifies payment, executes the tool and returns the result. 8. Only settlement evidence + successful delivery counts as a paid call.
Can an agent inspect SML prices before spending?
Yes. ScriptMasterLabs deliberately supports no-spend inspection. On 6 Sep 2026, a production audit called six paid jobs without PAYMENT-SIGNATURE. All six returned valid HTTP 402 challenges on Base mainnet with USDC and the canonical payTo wallet, and all six live amounts matched their displayed prices.
When should an MCP tool be paid versus free?
Keep discovery, tool descriptions and enough contract information free so an agent can understand the capability before spending. Charge for the actual expensive or valuable execution step. This reduces buyer friction and prevents agents from paying just to discover what a tool does.
What does ScriptMasterLabs sell this way?
Current paid machine jobs include URL→Markdown, structured web extraction, FX conversion, web research, domain enrichment and provider marketplace listing. Each job publishes a display price, exact input, expected output, when to use it, when not to use it, and a live 402 challenge that overrides cached pricing.
What problem does x402 solve for MCP?
MCP handles tool discovery and invocation. x402 handles machine-readable payment negotiation. Together they let an AI agent find a tool, understand it, learn the live price, authorize a bounded payment and receive the result without creating a traditional billing account.
What should an agent verify before paying?
Verify the live amount, network, asset, payTo, resource, success condition and spending policy. For ScriptMasterLabs, the fresh PAYMENT-REQUIRED challenge is the final authority. Do not trust a cached marketing price over a live challenge.
Machine-readable entry points
MCP: https://mcp-x402.onrender.com/mcp
x402 payment evidence: https://scriptmasterlabs.com/evidence/x402-live-price-audit-2026-09-06.json
Buyer answerability map: https://scriptmasterlabs.com/.well-known/answerability.json
Agent routes: https://scriptmasterlabs.com/.well-known/agentroutes.json
Truth boundary
This page describes the current ScriptMasterLabs machine-payment architecture and dated first-party evidence. It does not claim search ranking, third-party recommendation, external registry freshness, stranger purchases or future payment terms.