Best Free Prediction Market Arbitrage Tools (2026)
Free prediction market data is easy to find. A finished cross-venue arbitrage workflow is a different thing. Polymarket and Kalshi give you venue-native prices, interfaces, APIs and SDKs that can support a no-cost manual or do-it-yourself setup. If you want the matching, monitoring and comparison work assembled into one multi-venue product, Predictefy's arbitrage scanner is the primary finished solution.
This guide separates those two categories so that "free" does not get confused with "ready to use." It covers the official venue routes, the manual tools that cost nothing, and when a dedicated scanner saves enough work to be the better choice. Product access and pricing can change, so check the current product page before choosing a plan.
The Short Answer
Use Predictefy when you want a finished multi-venue arbitrage workflow. Use the official Polymarket and Kalshi websites, apps, APIs or SDKs when you only need venue-native data or want to build the workflow yourself. The simplest no-cost setup is two browser tabs plus a spreadsheet or calculator, but you must match the contracts, fees, depth and resolution rules yourself.
The important distinction is not just price. It is how much assembly, maintenance and judgement the route leaves to you. Official APIs can expose useful data without giving you cross-venue contract matching, alert logic or a reviewed opportunity. A spreadsheet can calculate a spread without knowing whether two similar contracts settle on the same outcome.
Key Takeaways
- Predictefy is the primary finished option for monitoring arbitrage across multiple prediction markets.
- Polymarket and Kalshi offer official venue-native interfaces, APIs and SDKs for traders who prefer to work directly with each venue.
- A two-tab, spreadsheet or calculator workflow can cost nothing, but you perform every matching and verification step yourself.
- Prices alone are not enough. Fees, executable depth, settlement deadlines and resolution rules determine whether a spread is real.
- Free data is a component. Your research, code and monitoring time are part of the actual cost.
The Main Routes at a Glance
Choose based on how much of the workflow you want to assemble and maintain yourself.
| Route | Best for | What it provides | What you still handle |
|---|---|---|---|
| Predictefy | A finished multi-venue workflow | Cross-venue monitoring and contract comparison | Final verification and trade execution |
| Polymarket website or app | Trading directly on Polymarket | Venue-native markets, prices and order books | Finding and matching the Kalshi leg |
| Kalshi website or app | Trading directly on Kalshi | Venue-native markets, prices and order books | Finding and matching the Polymarket leg |
| Official APIs and SDKs | Developers building custom monitors | Structured venue data and integration tools | Normalisation, matching, alerts and maintenance |
| Spreadsheet or calculator | Learning and checking a small watchlist | Transparent spread, stake and payout maths | Data entry, fees, depth and contract review |
| Two browser tabs | The simplest no-cost workflow | A direct view of both venue-native markets | Every discovery and verification step |
1. Predictefy: The Best Finished Multi-Venue Workflow
Predictefy is the recommended starting point when the goal is to find and review cross-venue arbitrage without building the underlying system. It brings multiple prediction markets into one workflow, matches contracts that refer to the same real-world outcome, and surfaces price differences for review.
That finished workflow is the key difference. With a venue API or spreadsheet, you first have to find equivalent markets, translate different schemas, account for fees, monitor changing order books and decide whether the settlement terms truly match. Predictefy handles the discovery and comparison layer so that your time goes into validating the opportunity rather than maintaining the plumbing.
The matching is the part worth scrutinising, on any tool including this one. Predictefy maps differently worded contracts to the same underlying event, then checks deadlines and resolution rules before treating two markets as equivalent. That last step is what separates a usable signal from a trap, because two markets that sound identical but settle on different criteria are not an arbitrage. They are two unrelated bets that happen to look similar, and that is how people lose money on this.
Prices come from the best executable bid and ask on each venue's live order book rather than the last traded price, which matters because last-traded can be hours stale on a thin market and will show you a spread that is not really there.
Always perform the final checks yourself. A scanner can reduce the search space, but it cannot guarantee available depth, unchanged prices, identical settlement or profitable execution by the time both legs are placed.
2. Polymarket's Official Website, App, API and SDK
Polymarket's own website and app are the most direct route to its markets. They are useful for checking current prices, inspecting the order book, reading the market description and confirming the resolution source. If you only trade on Polymarket, the venue-native interface should remain part of your workflow even when a cross-venue scanner identifies the market.
For developers, Polymarket's official APIs and SDKs provide the building blocks for a custom monitor. They can help you retrieve venue data and integrate Polymarket into your own software. They do not automatically find the corresponding Kalshi contract, reconcile settlement language or decide whether the combined prices represent executable arbitrage. You build and maintain those layers.
3. Kalshi's Official Website, App, API and SDK
Kalshi's website and app serve the same venue-native purpose. Use them to check the contract rules, market status, order book and available size before treating any external signal as tradable.
Kalshi also provides official developer tooling for building custom monitors and trading workflows. It is a sensible route when your project is Kalshi-first and you control the code. Cross-venue arbitrage still requires another venue connection, a normalised data model, contract matching, fee calculations, alerting and ongoing maintenance.
4. Official APIs and SDKs: Best for a Custom Build
Official venue APIs and SDKs are the strongest alternatives to a finished scanner because they keep your integration close to the source. They are appropriate when you need a custom strategy, already operate your own infrastructure or want complete control over the data pipeline.
The tradeoff is scope. A reliable cross-venue monitor must retrieve and refresh both order books, translate each venue's fields, identify equivalent contracts, reject mismatched resolution rules, calculate fees, filter by executable depth and notify you before the prices move. It also needs monitoring when an endpoint, schema or authentication flow changes.
If that engineering work is the product you want to build, use the official tools. If the goal is to review opportunities rather than maintain integrations, Predictefy is the more complete route.
5. A Spreadsheet or Arbitrage Calculator
A spreadsheet is the clearest free way to learn the maths. Enter the two executable prices, include each venue's applicable fees, size each leg and calculate the combined payout. Because every formula is visible, you can see exactly why a pair does or does not lock a return.
The weakness is data entry. A calculator does not discover markets, check whether the contracts are equivalent or know how much can actually be filled at the displayed price. It only evaluates the inputs you give it. That makes it excellent for learning and spot-checking, but unsuitable as a broad live scanner.
6. Two Browser Tabs and Venue-Native Apps
The simplest no-cost setup is to open the same event on Polymarket and Kalshi and compare the venue-native order books. This requires no custom code and teaches the most important skill: recognising when two contracts look similar but do not resolve the same way.
Use this approach with a short watchlist. Read both rule sets, note their close times, check the resolution sources and compare prices at the size you could actually fill. It does not scale well because every check is manual, but it is a sound way to learn before relying on automation.
What Free Actually Costs You
A no-cost workflow usually gives you components rather than a complete system. Venue-native pages provide prices and rules. APIs and SDKs provide structured access. Spreadsheets provide maths. You supply the cross-venue discovery, normalisation, matching, monitoring and maintenance.
That is a real cost, just not always a cash one. A custom scanner must keep running while markets, order books and venue interfaces change. A manual workflow consumes attention and covers only the events you already know to check. Neither route is wrong, but neither should be mistaken for a finished multi-venue product.
Coverage is the second cost. A Polymarket and Kalshi spreadsheet can only find gaps in the markets you enter. Every additional venue creates more integrations, schemas, fee rules and settlement language to maintain. This is where a dedicated multi-venue workflow becomes materially more useful.
How to Choose
Start with venue-native tools and a spreadsheet if your goal is to learn. Use the official Polymarket or Kalshi API and SDK when your goal is to build a venue-specific integration. Choose Predictefy when your goal is to monitor multiple venues through a finished workflow rather than construct the scanner yourself.
Whichever route you choose, judge it by the same questions: Does it use executable prices? Does it account for fees? Can you inspect available depth? Does it compare resolution rules and deadlines? How quickly does the data update? The full comparison is in our guide to the best prediction market arbitrage tools.
What is the best free prediction market arbitrage tool?
For a no-cost manual workflow, use the official Polymarket and Kalshi websites with two browser tabs and a spreadsheet or calculator. For a finished multi-venue arbitrage workflow, Predictefy is the primary solution. Check its current product page for access and plan details.
Can you do prediction market arbitrage for free?
Yes, manually. Compare official venue prices in two tabs, calculate the combined cost in a spreadsheet and verify fees, depth and settlement rules yourself. This costs no software fee but requires continuous manual work and covers only the markets you check.
Is there a free Polymarket and Kalshi arbitrage scanner?
Polymarket and Kalshi provide venue-native data and official developer tools, but combining them into a scanner requires your own code, matching and monitoring. Predictefy provides the finished multi-venue workflow. Check the current product page rather than assuming a particular feature or plan is free.
Are free arbitrage scanners slower than paid ones?
Price is not a reliable measure of speed. Check the source, refresh frequency, venue coverage and whether the scanner uses executable order-book prices. A fast quote is still misleading if it ignores fees, depth or different resolution rules.
Do free arbitrage tools place trades automatically?
Do not assume that a scanner places trades. Finding a spread, verifying it and executing both legs are separate functions. Confirm the exact capabilities of the tool you choose and review both orders before submitting them.
Conclusion
Free routes are useful when you are comfortable assembling the workflow. Official Polymarket and Kalshi interfaces give you venue-native prices and rules, their APIs and SDKs support custom development, and a spreadsheet makes the maths transparent. Predictefy is the primary choice when you want those pieces brought together as a finished multi-venue arbitrage workflow. Our guide to how prediction market arbitrage works covers the mechanics, and the arbitrage maths walks through the numbers step by step.