Unified Prediction Market API (2026): One Schema for 15+ Venues

What is a unified prediction market API?

It is one API that sits in front of many prediction market venues and returns their data in a single, consistent format. You ask for markets, an order book or price history, name the venue, and get the same record shape whichever venue answered.

Without one, every venue is its own integration. In our checks on 16 October 2026, the most active Polymarket market and an open Kalshi market came back looking nothing alike:

Multiply that by every venue you want, then add separate auth schemes, pagination styles, rate limits and order book formats. That is the cost a unified API absorbs once, for everyone.

What does normalization actually cover?

Good normalization is more than renaming fields. In a unified prediction market API it should cover:

• Identifiers. One market ID and one outcome ID format, so books, trades and candles are always keyed the same way.
• Prices. Every outcome price as a probability between 0 and 1, whatever the venue publishes natively.
• Records. The same fields on every market: title, outcomes with prices, 24-hour volume, liquidity and close date.
• Pagination. One set of list parameters (limit, offset, page and a cursor) instead of each venue's own.
• Freshness and source. A timestamp and a provenance label on each record, so you can tell live data from stored data.
• Capabilities. A per-market statement of what you can do with it, such as read, trade, depth and history.

Predictefy's documentation puts it as "one normalized schema across every supported venue". It also draws a careful line between the two kinds of empty value: null means a value applies but the venue does not publish it, while a missing field means it does not apply to that record at all.

How does Predictefy's unified API work?

Reads use one route pattern on one host:

GET https://data.predictefy.com/api/{venue}/{verb}
Authorization: Bearer pk_live_YOUR_KEY

Every response uses the same envelope, { success, data, meta, page }. A market inside data carries marketId, title, outcomes (each with its own outcomeId, label and price), volume24h, liquidity, asOf, provenance and capabilities.

A special venue called router searches across all served venues at once, which is how you look for the same topic everywhere in one call.

What does a first call look like?

With a free key, this lists the most active Polymarket markets:

curl -s "https://data.predictefy.com/api/polymarket/fetchMarkets?limit=3&sort=volume" \
  -H "Authorization: Bearer pk_live_YOUR_KEY"

The same thing from TypeScript, plus a search across every venue:

import Predictefy from '@predictefy/sdk';

const client = new Predictefy({ apiKey: process.env.PREDICTEFY_API_KEY });

// One venue
const markets = await client.polymarket.fetchMarkets({ limit: 5, query: 'fed' });
for (const m of markets) {
  console.log(m.title, m.outcomes.map((o) => `${o.label} ${o.price}`).join(' / '));
}

// Every venue at once
const all = await client.router.fetchMarkets({ query: 'election', status: 'active', limit: 10 });
console.log(all.length, 'markets across venues');

What can you build once the schema is unified?

The obvious win is less code. The bigger one is that cross-venue work becomes possible at all:

• Matched markets. The same event listed on Polymarket and Kalshi, grouped into one cluster so you can compare them side by side.
• Price comparison. One question, every venue's price, in one response.
• Screeners and dashboards that rank markets from every venue by volume, liquidity or price move.
• Backtests that run the same strategy on several venues' history.
• AI agents that read any venue through one tool set, via the Predictefy MCP server.

For the cross-venue side specifically, see how to find cross-platform opportunities between Kalshi and Polymarket.

Unified API or each venue's own API?

If you only ever need one venue, its own API is a fine place to start, and our Kalshi API vs Polymarket API comparison covers the two biggest. Once a second venue enters the picture, a unified API usually pays for itself in the code you never write.

Frequently Asked Questions