about tellmarket.

Tellmarket is a cross-exchange arbitrage scanner for prediction markets. We aggregate live data from Kalshi and Polymarket and surface every price gap with positive net edge after fees.

why this exists

Prediction markets are fragmented. The same outcome — “Will the Fed cut rates in December?” — can trade at 47¢ on Kalshi and 42¢ on Polymarket at the same moment. That gap is an arbitrage opportunity, but finding it requires watching both books in parallel and doing fee math in your head. Bots do this in milliseconds; humans don’t stand a chance unless they have a tool.

Tellmarket is the tool. We pull both orderbooks every 30 seconds, match markets across platforms using embedding similarity, calculate the realistic net profit after fees and slippage, and show you only the opportunities that actually pay.

how it works

we scan

Every 30 seconds we pull the orderbook for thousands of active markets on Kalshi and Polymarket.

we match

An embedding-similarity matcher pairs markets across platforms that describe the same outcome.

we calculate

For each pair we compute the net edge after exchange fees, slippage at the best available size, and a realistic position cap.

you decide

We don’t take your money or place trades. You open Kalshi or Polymarket directly and decide if the opportunity is worth taking.

what we do not do

We are not a broker, exchange, or financial adviser.

We do not place trades. We do not hold customer funds. We do not issue investment advice or recommendations. Every “open on” link takes you to the original exchange where you transact directly with them under their terms.

data sources

Kalshi — public orderbook via kalshi.com API. CFTC-regulated US exchange.
Polymarket — public orderbook via polymarket.com CLOB API. CFTC-regulated as of Dec 2025 via the QCEX acquisition.
DraftKings — game lines and sport futures via The Odds API. NBA, NFL, MLB championship winners + NBA h2h moneylines.

stack

Web — Next.js, Tailwind, hosted on Vercel
Mobile — React Native via Expo, on iOS
Backend — Supabase (Postgres + auth) for storage, Stripe for web payments, RevenueCat for mobile payments
Ingestion — Python service on Fly.io, polling exchanges every 30 seconds and writing matched opportunities to Supabase

built by

Kamyar · solo founder

Building Tellmarket because the same arbs HFT bots catch in milliseconds should be visible to anyone with a $500 bankroll.

contact

Reach out at support@tellmarket.app — for support, partnerships, press, or what would make the product better.

see live arbs →