About Superstables

Agents increasingly pay for what they use: data feeds, GPU and compute time, tools, and other agents. Those services announce their prices over payment protocols such as x402, MPP and ACP, on chains such as Base, Solana, Tempo and Robinhood Chain, in stablecoins such as USDC, EURC, USDT, PYUSD and USDG. Superstables collects those announcements into one directory so an agent, or the person building one, can find something payable and check that it actually works before calling it. Next to the services agents pay for, the index also lists on-chain places for idle balances: RWA yield vaults, tokenized stocks and stablecoin yield.

The index is free for humans and for agents. There is a web directory, a public JSON API with no key and CORS open, an MCP server, and a natural-language endpoint. Listing a service is free as well. There are no paid tiers and no paid placement; if that ever changes, pricing.md changes first.

A crawler reads public directories of payable services on a schedule, normalises chains, assets and prices, and merges entries that point at the same endpoint host. Every entry keeps a record of the sources it was found in, so provenance is never lost.

Each HTTP endpoint is then probed on a rolling schedule with a plain GET request that identifies itself as SuperstablesCrawler. A service is marked live when it answers with a payment challenge: an HTTP 402 status, a payment-challenge response header in the x402 v2 style, or an x402 or MPP challenge body. Endpoints that are not HTTP, such as acp:// addresses, are listed but never marked dead. Probe history is kept and shown on every service page, and services that stop appearing in their sources are delisted after seven days.

Superstables does not operate a payment rail, a facilitator, a chain or a stablecoin, and does not take a fee on anything listed. Ranking in the directory follows liveness and recency, not commercial relationships. Field names in the API are treated as a stable contract so that agents can integrate once.

Superstables indexes and probes. It does not execute, route or settle payments, and it never holds funds. The wider product described on the homepage, a payment router for agents, is the roadmap: a router across rails, then a control plane with policies and treasury basics, then agent identity and trust. The index is the part that exists today, and the reason it is public is that a router is only as good as its map.

The fastest way in is the machine-readable material:

• llms.txt: the site index written for agents
• API reference and OpenAPI spec
• MCP server card
• Authentication: none required
• Privacy: what we store and why