Alpaca API guide

What Alpaca is and who it suits

Alpaca Securities is a FINRA member broker-dealer (SIPC) offering commission-free trading in US-listed stocks and ETFs, fractional shares, and spot crypto through Alpaca Crypto. It has no desktop platform to speak of: the product is the API, which is why it is so popular with developers, quant hobbyists and fintech apps.

• Good fit: daily or intraday strategies on US equities, ETFs and major crypto pairs; anyone who wants paper trading that behaves like the live account.
• Less suited: forex, futures or non-US equities (not offered), and high-frequency strategies that need co-location.

Paper vs live: two accounts, two key pairs

Every Alpaca user gets a paper account with simulated cash that can be reset at any time. Paper and live accounts have separate API keys and separate base URLs: paper keys only work against https://paper-api.alpaca.markets and live keys only against https://api.alpaca.markets. Mixing them is the single most common cause of a 401 Unauthorized or 403 Forbidden response.

Alpaca market data plans

The same key pair also authenticates the Market Data API. The free Basic plan streams real-time IEX quotes for up to 30 WebSocket symbols, serves historical stock bars back to 2016 and allows about 200 historical calls per minute. Algo Trader Plus ($99/month) adds all US exchanges (SIP), unlimited WebSocket symbols and up to 10,000 historical calls per minute. Crypto data is free on every plan.

Rate limits and practical limits

The trading API allows about 200 requests per minute per account, and returns 429 Too Many Requests beyond that. A bar-close strategy that checks once per bar is nowhere near the limit; a loop that polls every second for many symbols can be. Stocks trade only in US market hours (plus extended hours for limit orders); crypto trades around the clock.

• Alpaca moved to FINRA’s new intraday-margin framework on June 4, 2026, replacing its old pattern-day-trader handling; older guides quoting the $25,000 PDT rule as an Alpaca limit are out of date.
• Crypto orders support gtc and ioc time-in-force; stock market orders are usually day.
• Fractional orders are market or limit orders during regular hours only.

Use Alpaca in AlgoGP

Open a project, go to the APIs & keys tab and, under Platforms, pick Alpaca as the market data source (market_data.py) and the broker (brokers.py). The choice is saved to config.json as a new strategy version:

{
  "platforms": {
    "data": "alpaca",
    "broker": "alpaca"
  }
}

• TRADING_MODE=paper (default): simulated fills on your machine; the broker is never contacted.
• TRADING_MODE=sandbox: orders go to Alpaca’s paper trading account with simulated fills.
• TRADING_MODE=live: real orders, and only once LIVE_TRADING_ACKNOWLEDGED=yes is set.

New to Alpaca? Follow the step-by-step Alpaca API key guide.