Polymarket market data (read-only)

Public Polymarket order books turned into engine quotes. Read-only: no orders, no signing, no wallet.

Read-only

The client can reach one host, the public Polymarket order-book API, over HTTPS with no redirects, and only sends GET requests. Nothing is signed and no wallet or key is involved. Orders are not built: they settle in real USDC on Polygon, and the main platform is not available to US persons.

What it reads

• The list of active markets, page by page, with each outcome token and its tick size.
• The order book of one outcome token, turned into a quote: the highest bid and the lowest ask with their sizes, whatever order the levels arrive in.

Exact values

• Prices are between 0 and 1. The price precision comes from the tick: 0.01 gives 2 decimals, 0.001 gives 3, 0.0001 gives 4; any other tick is refused.
• Sizes use 2 decimals, the most seen in the captured books. A value with more decimals refuses the book; it is never rounded.
• A book with an empty side gives no quote. A crossed book, a zero size, a duplicate price or a book for a different token is an error.

Instrument ids

Outcome token ids are up to 78 digits. The engine id is POLY. followed by the token id in base 36, which is unique and reversible and fits the 64-character limit.

Command line

fth-poly markets [limit=<n>]
fth-poly book <token_id>

Status

Real for public data: the commands have run against the live public API (2026-11-11). Tests run on trimmed real captures. Using the data for anything beyond research is up to the reader; prices are market quotes, not advice.

Official reference

Polymarket publishes its order-book API reference in its developer documentation. This page describes the engine's adapter; it does not restate Polymarket's documentation.