The latest articles on DEV Community by Superstables (@superstables). https://dev.to/superstables https://media2.dev.to/dynamic/image/width=90,height=90,fit=cover,gravity=auto,format=auto/https:%2F%2Fdev-to-uploads.s3.us-east-2.amazonaws.com%2Fuploads%2Fuser%2Fprofile_image%2F4128984%2F9874a900-f063-4db3-a0b2-fc435cd2d79f.png https://dev.to/superstables en Superstables Thu, 17 Sep 2026 03:33:27 +0000 https://dev.to/superstables/we-probed-2300-x402mpp-payable-endpoints-heres-what-payable-actually-means-in-practice-43m https://dev.to/superstables/we-probed-2300-x402mpp-payable-endpoints-heres-what-payable-actually-means-in-practice-43m <p>Quick context, in case you haven't run into this yet</p> <p>AI agents are starting to need to <em>pay</em> for things on their own — call an API, get<br> charged a few cents in stablecoin, get the data back, no human clicking "buy." The<br> standard emerging for this reuses an old, mostly-unused HTTP status code: <strong>402<br> Payment Required</strong>. An agent hits an endpoint, gets a 402 back with a price, pays in<br> USDC (or similar), retries the request, gets the real response. That's <strong>x402</strong><br> (and its cousins MPP and ACP — same idea, different implementations).</p> <p>Separately, <strong>MCP (Model Context Protocol)</strong> is the standard that lets AI assistants<br> (Claude, etc.) connect to external tools and data in a consistent way — instead of<br> every company inventing its own integration format.</p> <p>We run <strong>Superstables</strong>: an index that sits at the intersection of both. It tracks<br> every service an agent can pay for via x402/MPP/ACP, and exposes that index through<br> an MCP server, so any MCP-compatible agent can query it directly.</p> <h2> The problem we ran into </h2> <p>Building the index was the easy part. The hard part: a lot of what gets "listed" as<br> payable across various sources doesn't actually work anymore — dead demos, abandoned<br> projects, services that changed their pricing or auth and never updated anywhere.</p> <p>So we started probing. Every endpoint in the index gets a real HTTP request on a<br> rolling schedule, and only gets marked "live" if it responds the way a real payable<br> endpoint should (HTTP 402 with a valid payment-challenge, or an x402/MPP challenge<br> body). Right now: <strong>2,328 services indexed, only 1,472 (~63%) actually live.</strong></p> <p>If your agent's only source of truth is a static list, roughly a third of its calls<br> are hitting something dead.</p> <h2> What it looks like in practice </h2> <p>Ask the MCP server directly (no auth, no key):</p> ai webdev api opensource