Arbitrage tools for cross-venue prediction market trading

What to build

A cross-venue prediction-market toolkit for retail traders — built on Layer's unified API — that scans Kalshi and Polymarket simultaneously for mispriced or divergent odds on the same event, and surfaces the spread via a web dashboard or a Telegram/Discord alert bot.

Layer collapses two separate prediction-market integrations (Polymarket, Kalshi) into one API, making it cheap for a solo builder to ship arbitrage-scanning or odds-comparison tools that previously required maintaining two separate exchange integrations.

Demand

Retail interest in prediction markets has surged alongside election and macro betting activity, and traders already manually compare Kalshi vs. Polymarket odds on Twitter/Discord — a tool that automates that comparison targets an active, underserved niche.

• Hacker News (Show HN)Launch

  Show HN: Layer – One API for Polymarket and Kalshi — 3 points, 1 comment. Builder David describes it as an API + SDK to build on top of both venues.

Stack

• Layer API/SDK
• Polymarket API
• Kalshi API
• Next.js
• Telegram Bot API
• Supabase

Solo + AI difficulty

Easy to get a basic odds-comparison dashboard or alert bot working in a few days once Layer's API is wired up, since it removes the need to integrate two separate venue APIs; the hard part is handling fee/withdrawal differences and settlement timing correctly so displayed 'arbitrage' is real, plus depending on an unproven third-party API's uptime. Rough time-to-MVP: 1-2 weeks for a solo builder using AI-assisted coding.

Entry threshold

Low barrier if Layer's API stays free or cheap during early access; a solo builder can wrap it into a bot or dashboard in days, but the opportunity depends entirely on a third-party API's reliability, pricing and continued access, and the underlying arbitrage edge shrinks as more bots compete for it.

Window

6-12 months

Where to find first users

• r/Kalshi and r/predictionmarkets
• Prediction-market Discord/Telegram communities
• Show HN / Product Hunt launch
• Indie hacker and quant-trading Twitter

Counter-signals & risks

• Polymarket and Kalshi operate under different regulatory regimes (offshore/crypto-based vs. CFTC-regulated US exchange), which may limit the practical overlap of users who can legally trade on both, reducing real-world arbitrage opportunities.

• Fees, withdrawal friction, and settlement/liquidity differences between the two venues could erode or eliminate apparent cross-venue spreads, undermining arbitrage-tool viability.

• As a new Show HN launch with no historical signal match, Layer's API reliability, uptime, and long-term maintenance are unproven, posing integration risk for anyone building on top of it.