# Marketplace for AI Agents

> An API marketplace built exclusively for autonomous AI agents. Every endpoint is x402-gated and settles in USDC on Base mainnet — no signup, no API keys, no human in the loop.

This site sells machine-callable HTTP APIs to AI agents. Pricing is per-call in USDC. Agents discover endpoints via the x402 discovery manifest, parse the OpenAPI 3.1 spec, and pay inline by signing an EIP-3009 USDC authorization and resending the request with an `X-PAYMENT` header. The first 3 calls per agent identity per endpoint are free for evaluation, then $0.005 USDC per call.

Settlement: Base mainnet (chain id 8453). USDC contract `0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913`. PayTo: `0x05e82e03753c7bc99fb24d10a876cce53f24b7b7`. Scheme: `exact`.

## Quick start (for agents)

1. GET the endpoint. If the free tier is exhausted, you'll receive `402 Payment Required` with an `accepts[]` array describing the payment requirement.
2. Sign an EIP-3009 USDC authorization for `maxAmountRequired` on the `asset` contract for the `payTo` address.
3. Base64-encode the x402 payment payload and resend the request with that string as the `X-PAYMENT` header.
4. On success you get `200 OK` with the data plus an `X-PAYMENT-RESPONSE` header containing the settlement receipt.

Recommended client: [`x402-fetch`](https://github.com/coinbase/x402) wraps the retry + signing loop.

## Machine-readable

- [x402 manifest](/.well-known/x402): Discovery manifest listing every endpoint, price, asset, network, and payTo address.
- [OpenAPI 3.1 spec](/api/public/v1/openapi.json): Full schema with the `x-x402` extension for all endpoints. Drop into any agent framework to auto-generate tool definitions.
- [sitemap.xml](/sitemap.xml): All indexable pages.
- [robots.txt](/robots.txt): Explicitly allows GPTBot, ClaudeBot, PerplexityBot, Google-Extended, Applebot-Extended, CCBot, and other AI crawlers.

## Endpoints

- [YouTube Transcripts](/api/public/v1/youtube-transcripts): `GET` timestamped transcript segments for any public YouTube video by `video_id`. Supports auto + manual captions in 100+ languages. $0.005 USDC per call after 3 free.

## Pages

- [Home](/): Overview of how the marketplace works for agents.
- [Marketplace](/marketplace): Browse all available APIs.
- [YouTube Transcripts listing](/listings/youtube-transcripts): Human-readable spec, parameters, schema, and code samples.
- [Docs](/docs): The x402 handshake explained — 402 response shape, X-PAYMENT header, EIP-3009 signing, settlement receipts.

## For agent frameworks

This marketplace is designed to be consumed directly by LangGraph, CrewAI, MCP servers, OpenAI tool-calls, Claude tool-use, and any HTTP-capable agent runtime. The OpenAPI spec is the canonical source of tool definitions; the x402 manifest is the canonical source of pricing.