layer
LIVEkalshi · polymarket

One API for prediction markets.

Layer gives developers one interface to find markets, stream normalized data, place orders, and track positions across Kalshi and Polymarket. Build your trading system once instead of rebuilding venue plumbing.

01 matchFind the same event02 compareSee live prices03 costsKnow your true costs04 tradePlace and cancel orders05 trackFills and positions06 testBacktest on history
01 matchLIVE

Same bet, not just the same words

Kalshi and Polymarket word the same bet differently, and sometimes settle it differently. Layer reads both venues’ settlement rules, flags where they differ, and checks every match again once it settles.

Reads both venues’ settlement rules
Flags different resolution sources
Re-checks when a venue edits its rules
Checks every match after it settles
live match · Fed decision, December 2026
kalshiWill the Federal Reserve cut rates by 25bps at their December 2026 meeting?settles on · federalreserve.gov
polymarketWill the Fed decrease interest rates by 25 bps after the December 2026 meeting?settles on · the FOMC statement
layersame bet · 0.85 confidence · caveat: rounding differs
02 compareCOMING SOON

See the market in real time

Prices, spreads, and liquidity for matched markets, side by side. See which venue has the better trade.

Live pricesBest bid / askOrder booksWebSocket streams
market · yeskalshi bidkalshi askpoly bidpoly askgap
Fed cuts 25 bps in December0.410.430.390.41+0.00
Rams beat Eagles, Oct 40.640.660.630.65-0.01
Chiefs beat Raiders, Oct 40.710.730.680.70+0.01
CPI above 3.0% in October0.510.530.500.52-0.01
One WebSocket for prices, order books, and fills. Same message format for both venues.illustrative prices · gap = best bid on one venue minus best ask on the other
ws · prices, books, fillslive
09:41:12.000pricekalshi FED_DEC_C25 bid 0.40 ask 0.42
09:41:13.241bookpolymarket KC_LV yes 0.71 +1,200
09:41:14.482pricepolymarket FED_DEC_C25 bid 0.39 ask 0.41
09:41:15.723fillkalshi FED_DEC_C25 yes 100 @ 0.42
09:41:16.964bookkalshi FED_DEC_C25 yes 0.41 −300
09:41:17.205pricekalshi LAR_PHI bid 0.62 ask 0.64
03 costsLIVE

Know your true costs

A quoted price isn’t your price. Layer breaks down fees, spreads, and estimated slippage per trade, so your strategy prices reality instead of the quote.

Fees
Spreads
Estimated execution costsCOMING SOON
Net profitability
Size you can actually tradeCOMING SOON
Return per day of capital held
Fed cuts 25 bps in December · 100 contracts · example
buy yes · kalshi @ 0.42$42.00
buy no · polymarket @ 0.55$55.00
payout at resolution$100.00
gross gap+$3.00
kalshi fee−$1.71
polymarket fee−$0.00
est. slippage−$0.50
net+$0.79
illustrative · fees vary by venue and market
04 tradeCOMING SOON

Execute through one interface

Same call to place or cancel an order on Kalshi or Polymarket. Change the venue, keep the code.

Place ordersCancel ordersCross-venue executionLeg-risk guard: unwind if one side doesn’t fillCOMING SOON
pythoncopy
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# buy yes on kalshi, no on polymarket a = client.buy( venue="kalshi", market=match.kalshi, side="yes", price=0.42, size=100 ) b = client.buy( venue="polymarket", market=match.polymarket, side="no", price=0.55, size=100 ) # same cancel on either venue client.cancel(b.id) # same order shape back a.status # "filled" a.filled # 100 @ 0.42
05 trackCOMING SOON

Know what actually happened

After an order is sent: what filled, what you hold, and where your money is, in one shape across venues.

Fills
Positions
BalancesCOMING SOON
P&LCOMING SOON
Resolution stateCOMING SOON
fillssame shape
kalshi · FED_DEC_C25 · yesfilled100 @ 0.42$42.00
polymarket · FED_DEC_C25 · nofilled100 @ 0.55$55.00
positionsone view
kalshi · FED_DEC_C25yes 100polymarket · FED_DEC_C25no 100
illustrative fills
06 testCOMING SOON

Test before you trade

Replay real order books, not last-trade charts, with fees and fill simulation, before risking real money.

Historical pricesCOMING SOON
Historical order booksCOMING SOON
Fill simulation at real depthCOMING SOON
Strategy researchCOMING SOON
BacktestingCOMING SOON
developer experience

One schema for both venues.

authOne API key
LIVE
prices0.00–1.00 everywhere
COMING SOON
ordersOne order model
COMING SOON
sdkPython and TypeScript
COMING SOON
reliabilityRetries, error normalization, and rate-limit handling built in, so venue quirks don’t break your system.
COMING SOON
CLICOMING SOON
WebhooksCOMING SOON
MCP · agent skillsCOMING SOON
roadmap

Prediction markets first. Built for automated trading across markets.

nowPrediction markets
LIVE
nextCrypto
COMING SOON
laterEquities
COMING SOON
laterTokenized assets
COMING SOON

Build on prediction markets.

Matching, prices, execution, and fills for Kalshi and Polymarket, without rebuilding the plumbing.