# AI Data Archive

> Machine-readable archive of open-licensed scholarly literature (Europe PMC, OpenAlex), normalized to structured JSON with full license/attribution metadata. Discovery and search are free; document content is paid per request via the x402 HTTP payment protocol (USDC).

## How to use
- Free: [API overview](/api), [catalog](/api/catalog), [search](/api/search?q=calibration), [topics](/api/topics), [discovery](/.well-known/ai-data.json), [OpenAPI](/openapi.json)
- Paid (x402, Base, USDC): /api/document/{id} ($0.001), /api/document/{id}/fulltext ($0.01), /api/document/{id}/references ($0.002), /api/topic/{slug}/content ($0.5)
- A paid endpoint answers HTTP 402 with a PAYMENT-REQUIRED header; retry with a PAYMENT-SIGNATURE header produced by an x402 client.

## Licensing
Only CC0 / Public Domain / CC BY / CC BY-SA documents are included. Each response includes license, license_url and attribution that must be preserved.