Official venue APIsAPIfree
PredictIt (older API): what it exposes, how it authenticates, where it stops
Last checked 2026-09-08
PredictIt's API is two public JSON endpoints: https://www.predictit.org/api/marketdata/all/ for every active market and /api/marketdata/markets/{id} for one. There is no authentication, no order entry and no history.
It is for anyone who wants free US political odds in a script. It is not a trading API, and its help article now sits behind a support login, so the terms below come from an archived copy.
What the API exposes
Each market carries an id, name, short name, image, URL, status, timestamp and a contracts array. Each contract exposes status, dateEnd, lastTradePrice, bestBuyYesCost, bestBuyNoCost, bestSellYesCost, bestSellNoCost and lastClosePrice. On 2026-09-08 the all-markets endpoint returned 186 markets and 590 contracts, all with status Open, led by 2026 midterm and 2028 nomination markets.
PredictIt's support article describes the feed as the latest trade price and best offers to buy and sell, updated every sixty seconds. There is no order book depth, no volume and no trade tape.
Authentication and rate limits
None. The endpoints are open. Because the data refreshes once every sixty seconds, polling faster than once a minute returns the same numbers. The single-market route needs the numeric id, which you read from the market URL or from the all-markets response.
Pricing and access
Free. The licence attached to the feed states the data is for non-commercial use and that PredictIt must be attributed as the source. There is no signup, no key and no documented way to request higher access.
Where it falls short
Read-only. You cannot place, cancel or read your own orders through it.
One-minute granularity and top-of-book only, with no historical endpoint, which rules it out for anything beyond a ticker or a daily snapshot job.
The documentation page that defined it is no longer publicly reachable; the live endpoint is the only current reference.
Who should use it
Dashboards, newsletters and research scripts that want PredictIt's political lines next to Kalshi and Polymarket prices. The bestBuyYesCost and bestSellYesCost pair gives you a bid and ask per contract, which is enough to compute a spread against another venue.
Traders should use it as a comparison feed only and execute through a venue with a real order API.
Questions about PredictIt (older API)
Is the PredictIt API free?
Yes. No key is required, and the licence allows non-commercial use with attribution to PredictIt.
How often does the PredictIt API update?
Every sixty seconds, per PredictIt's support article.
Can I trade on PredictIt through the API?
No. It exposes read-only market data: last trade price and best buy and sell prices per contract.
Official APIs for building. One book for trading.
Rather trade the spread than build the plumbing? The free Kairos terminal gives you Kalshi, Polymarket and Predict.fun in one order book.