Kalshi API

CFTC-regulated US event exchange. USD-denominated binary contracts settle at $1.00 (YES wins) or $0.00 (NO wins). REST + WebSocket, RSA-PSS authentication on every request.

For contract semantics and settlement rules, see the kalshi-weather-markets and kalshi-crypto-index-markets skills. For strategy, sizing, and backtesting, see prediction-market-strategy.

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VERIFY BEFORE CODING. The Kalshi API has broken backward compatibility before: the host changed (old trading-api.kalshi.com → dead), and the order schema changed (integer cents → dollar strings). Always smoke-test signing and order bodies against a live response before shipping.

Canonical sources:

• API reference: https://docs.kalshi.com (legacy mirror: https://trading-api.readme.io)
• Official Python starter: https://github.com/Kalshi/kalshi-starter-code-python

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Overview

• Base URL: https://api.elections.kalshi.com/trade-api/v2
• Auth: RSA-PSS on every request, there are no public/unauthenticated endpoints
• No demo parity: the demo environment (demo-api.kalshi.co) has a near-empty book; use production even for read-only pulls
• Contracts: $0.01, $0.99 per contract; pay price if YES wins, lose price if NO wins; max payout = $1.00

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Quick Start

1. Credentials

KALSHI_KEY_ID=<your-key-uuid>
KALSHI_PRIVATE_KEY_PATH=~/.kalshi/private.pem

Generate the key in the Kalshi dashboard. Store secrets in environment variables or a secrets manager, never in code.

2. Install

pip install httpx cryptography

3. Host + auth (the part everyone gets wrong)

The host and signature format are where implementations break. Three common failures:

1. Using the old trading-api.kalshi.com host → 401
2. Including the query string in the signed path → 401
3. Signing with seconds instead of milliseconds → 401