What Are Prediction Market APIs? A Beginner's Guide

Prediction markets processed over $44 billion in trading volume in 2025, and the ecosystem around them has grown fast. If you are new to this space, this guide will explain what prediction market APIs actually are, how the data is structured, which platforms matter, and how to get your first live data without writing a line of authentication code.

1. What is a prediction market API?

At its core, a prediction market API is an interface that lets developers pull real-time and historical data from prediction market exchanges. Depending on the platform, that data includes current contract prices, order book depth, trading volume, market resolution metadata, and in some cases the ability to place and manage trades directly.

Prediction markets price the probability of future events as contracts that settle between $0 and $1. So if a market is sitting at $0.62, the crowd collectively believes there is a 62% chance the event happens. The API exposes that data in machine-readable form, which opens the door to trading bots, analytics dashboards, arbitrage tools, academic research datasets, and live odds displays.

Traditional sports odds APIs deliver prices set by a bookmaker. Prediction market APIs work differently: prices emerge entirely from user activity on an open order book. That fundamental difference shapes the data structures, authentication requirements, and integration patterns you will encounter, which is exactly what this guide covers.

Quick stats: $44B+ trading volume in 2025   |   32+ active platforms globally   |   Prices range from $0 to $1 and represent implied probability

2. The major prediction market platforms

Before getting into the specifics of each API, it is worth understanding the broader landscape. Prediction market platforms fall into a few distinct categories, and each one has a meaningfully different API architecture:

• Regulated exchanges (e.g. Kalshi): CFTC-regulated, familiar REST APIs, fiat settlement, and institutional FIX protocol support.
• Crypto-native platforms (e.g. Polymarket): decentralised markets on blockchain infrastructure that require wallet authentication and on-chain interaction.
• Play-money platforms (e.g. Manifold Markets): no financial risk, very generous rate limits, and ideal for prototyping.
• Aggregators (e.g. FinFeedAPI, PolyRouter): unified APIs that normalise data from multiple platforms through a single endpoint. 

This guide focuses on Kalshi in depth, since it is the most developer-friendly starting point for anyone working with US-regulated data. For a deep dive into Polymarket, Manifold, aggregators, comparison tables, and use cases, see the companion article below.

Read part two: Polymarket, Kalshi & Aggregator APIs: Advanced Developer Guide

3. Kalshi API: CFTC-regulated, REST-first

Kalshi is the only CFTC-regulated prediction market exchange in the United States, sitting under the same regulatory framework as traditional futures exchanges. The API is built for developers who want a clean, conventional integration experience. If you have ever connected to Stripe or a standard financial data provider, Kalshi will feel immediately familiar.

The base URL for the production API is api.elections.kalshi.com/trade-api/v2, and Kalshi maintains a full sandbox environment at demo-api.kalshi.co that mirrors production exactly. Start there. It runs real-looking simulated markets and will save you a lot of debugging headaches before you go live.

Authentication

Kalshi uses RSA key-pair authentication rather than a simple bearer token. You generate a private key locally, register the public key through your Kalshi account settings, and then sign each request. It takes a bit more setup than a standard API key, but it is the level of security you would expect from a regulated financial exchange.

# Kalshi REST API: fetch current open markets
import requests

BASE_URL = "https://api.elections.kalshi.com/trade-api/v2"

headers = {
    "Authorization": "Bearer YOUR_TOKEN",
    "Content-Type": "application/json"
}

resp = requests.get(
    f"{BASE_URL}/markets",
    headers=headers,
    params={"limit": 10, "status": "open"}
)

markets = resp.json()["markets"]
for m in markets:
    print(m["title"], "-", m["yes_ask"])

Key endpoints

Once you have authentication working, these are the endpoints you will use most:

•        GET /markets: returns a list of open markets. You can filter by series, event category, or status. This is usually the first call in any integration.

•        GET /markets/{ticker}/orderbook: full order book depth for a specific market, including all bid and ask levels.

•        GET /events: event-level groupings that bundle related markets together (e.g. all markets within a single election).

•        POST /portfolio/orders: place a buy or sell order. Requires authentication and collateral in your account.

•        GET /portfolio/positions: your current open positions across all markets.

Real-time data via WebSocket and FIX

For anything that needs to be live, Kalshi offers a WebSocket API that pushes market updates as they happen rather than requiring you to poll. You subscribe to specific channels and receive diffs as prices move.

For institutional use cases where latency really matters, Kalshi also supports FIX 4.4, which is the same protocol used by stock and futures exchanges worldwide. For firms that already have FIX infrastructure, this makes the integration extremely straightforward. For most developers building analytics or display products, the REST or WebSocket API will be all you need.

Rate limits: Kalshi enforces 10 requests per second on most REST endpoints. If you need to scan hundreds of markets quickly, implement exponential back-off or switch to WebSocket subscriptions rather than polling.

Geographic restrictions

Kalshi is currently limited to US residents, and even then it is not available in eight states: Arizona, Illinois, Massachusetts, Maryland, Michigan, Montana, New Jersey, and Ohio. If you are based outside the US, you can still pull market data for research and display purposes, but you cannot trade.

4. Getting started: your first API call

The quickest way to get real prediction market data in front of you is to hit Polymarket's public CLOB endpoint. It returns live market data with no signup, no API key, and no authentication at all. Here is a working Python example you can run right now:

import requests

# No authentication required for public market data
url = "https://clob.polymarket.com/markets"
params = {
    "next_cursor": "",
    "limit": 10,
    "active": True
}

response = requests.get(url, params=params)
data = response.json()

for market in data["data"]:
    question = market.get("question", "N/A")
    yes_price = market.get("tokens", [{}])[0].get("price", "N/A")
    volume = market.get("volume", 0)
    print(f"{question[:60]}")
    print(f"  YES price: {yes_price}  |  Volume: ${volume:,.0f}\n")

# Paginate using: next_cursor = data["next_cursor"]

If you prefer to start with zero financial stakes, Manifold Markets is even simpler. Its API is fully public, needs no authentication for read operations, and uses a play-money currency so there is nothing on the line while you learn the data structures. Its documentation lives at docs.manifold.markets/api.

Once you are comfortable with how the data is shaped, move to Kalshi. Use the sandbox at demo-api.kalshi.co to set up your RSA key pair, explore the endpoints, and test your integration with simulated markets before you touch anything live.

Recommended path: Polymarket public API (no auth, live data) → Manifold Markets (play money, learn the structure) → Kalshi sandbox (real integration, no real money) → Kalshi production.

If you are looking for a unified prediction market API, then have a look at SportsGameOdds offering Kalshi, Polymarket and Novig in a developer-friendly API.

This article is maintained by the SportsGameOdds editorial team and updated regularly. Platform APIs change frequently, so always refer to official documentation for the most current endpoints and rate limits. This guide is for informational purposes only and does not constitute financial or trading advice.