about tellmarket.

Tellmarket is the honest terminal for prediction markets and sportsbooks. We pull live prices from Kalshi, Polymarket and DraftKings every 30 seconds, show you the best number on each question after fees, surface where the venues disagree — and flag the rare cross-exchange arb the moment one appears. We never fake it.

why this exists

Prediction markets are fragmented. The same outcome — “Will the Fed cut rates in December?” — can trade at one price on Kalshi and another on Polymarket at the same moment. Most of the time that gap just tells you which venue has the better number; once in a while it’s wide enough to lock a riskless arb. Either way, catching it means watching every book in parallel and doing fee math in your head — bots do it in milliseconds; humans don’t stand a chance without a tool.

Tellmarket is the tool. We pull the orderbooks every 30 seconds, match the same question across platforms using embedding similarity, calculate the realistic net profit after fees and slippage, and show you the best price, where the venues disagree, and the rare true arb — only what actually pays.

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 (paused; see changelog)
Backend — Supabase (Postgres + auth) for storage, Stripe for web 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 →