Agent-readable docs index: /llms.txt. Full docs in one file: /llms-full.txt. Download /docs.zip to grep all markdown files locally.

Book

GET /v1/book/{underlyingKey}/{specifier}
{
  "pos": 918274, "seq": 1834,
  "bids": [{ "price": 19000, "quantity": 40 }, { "price": 18500, "quantity": 12 }],
  "asks": [{ "price": 20000, "quantity": 15 }]
}
Every price level, bids best first, asks best first. 404 for no such contract.