kalshi-api

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.

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

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

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

import os, time, base64, httpx
from cryptography.hazmat.primitives import hashes, serialization
from cryptography.hazmat.primitives.asymmetric import padding

BASE = "https://api.elections.kalshi.com/trade-api/v2"
KEY_ID = os.environ["KALSHI_KEY_ID"]
with open(os.environ["KALSHI_PRIVATE_KEY_PATH"], "rb") as f:
    PRIV = serialization.load_pem_private_key(f.read(), password=None)

def _headers(method: str, path: str) -> dict:
    """path must include /trade-api/v2 prefix and exclude query string."""
    ts = str(int(time.time() * 1000))             # milliseconds
    msg = f"{ts}{method}{path}".encode()
    sig = PRIV.sign(
        msg,
        padding.PSS(mgf=padding.MGF1(hashes.SHA256()),
                    salt_length=padding.PSS.DIGEST_LENGTH),
        hashes.SHA256(),
    )
    return {
        "KALSHI-ACCESS-KEY": KEY_ID,
        "KALSHI-ACCESS-TIMESTAMP": ts,
        "KALSHI-ACCESS-SIGNATURE": base64.b64encode(sig).decode(),
    }

def get(path: str, params=None):
    # Sign the path only — query goes into params, not the signature
    r = httpx.get(BASE + path, params=params,
                  headers=_headers("GET", "/trade-api/v2" + path))
    r.raise_for_status()
    return r.json()

def post(path: str, body: dict):
    r = httpx.post(BASE + path, json=body,
                   headers=_headers("POST", "/trade-api/v2" + path))
    r.raise_for_status()
    return r.json()

# Example: open markets in a series
markets = get("/markets", params={"series_ticker": "KXHIGHNY", "status": "open"})