How Trading Works
What happens between tapping Buy and seeing the fill land.
TL;DR
The order book
Polymarket runs a CLOB — central limit order book. Buyers post bids, sellers post asks, the engine matches them in the middle. Celsa sends your orders straight to that book. We aren't a custodian and we don't see your order ahead of the matching engine.
The orderbook column to the right of every chart is a WebSocket feed — levels appear as they post and clear as they fill, frame-by-frame. If the socket flakes, a REST poll picks up the slack so you don't watch a frozen book.
A trade, step by step
Pick a market and an outcome
Your wallet signs
The relayer submits
The book matches
The fill appears
Market vs limit
Market
Fills against whatever's on the book right now. Fast. The catch: on a thin book the average fill price walks up — you might pay 5¢ more than the visible best ask if the top level only holds a few shares. We project that fill price before you confirm so the "you pay" line is honest.
Limit
You name your price. The order sits on the book until someone takes it or you cancel. Cheaper, but you wait. Time-in-force options (FOK / FAK / GTC / IOC) sit next to the limit toggle — for most rests you want GTC. The Order Types page covers each one with a one-line use case.
First-trade setup
The first time you ever click Buy, a one-time bootstrap runs in the background. About 30 seconds.
- ●Deploys your on-chain trading wallet (Gnosis Safe for legacy accounts; a smart-account deposit wallet for everyone post the May 2026 cutover)
- ●Mints your Polymarket API credentials and binds them to your wallet
- ●Approves the collateral token so the relayer can move funds on your behalf
Every subsequent trade skips all of that — one signature, a few hundred milliseconds. We also drop a small POL grant onto your wallet the first time you deposit, so you have gas for the rare manual on-chain action that the relayer doesn't cover.
Charts
We render the chart with lightweight-charts on a custom theme. Smooth line curves, a soft area fill under the YES line on binary markets, a magnet crosshair that snaps to the nearest data point so you can read prices precisely. Vertical gridlines are off — they add noise without information.
Multi-outcome events (election fields, weather temperature buckets, soccer three-way moneylines) draw every outcome as its own line. The legend below sorts by current ¢ descending and hides resolved outcomes; expand to see them.
Drag the handle under the chart to resize the chart + order book column together. We remember the height per panel type.
What the tabs below the chart do
- ●Outcomes — pick a sub-market on multi-leg events. Click flips the trade panel + chart focus.
- ●Trades — live fill feed. Rows flash green or red on print. REST-backed if the WebSocket hiccups.
- ●Top Traders — wallets with the largest combined PnL on this market. Side, total bought, average entry, current PnL, and a bar showing how much of the original position is still open.
- ●Holders — biggest YES + NO holders. Tap any name to open their wallet profile.
- ●News — relevant articles and the full resolution criteria. Weather markets also surface an ensemble forecast widget here.
- ●Threads — Polymarket's discussion thread, embedded.
- ●Whales — recent whale fills on this exact market.
- ●Related — sibling markets in the same event.
- ●My Positions / My Orders — your own state on this market.
Resolution
Each market spells out its resolution rules on the News tab. When the market resolves, winning shares pay out at $1.00 each and losing shares go to zero. Head to Portfolio to redeem winners — the claim button surfaces automatically.