Alpaca Markets API
Commission-free US equity and crypto brokerage API with paper trading, real-time market data streaming, and broker API for building trading products on top of Alpaca's regulated clearing infrastructure.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
API keys are single-permission (full account access); no per-action scoping. OAuth2 Broker API allows delegated access with user consent. SIPC insurance covers brokerage accounts. Paper trading keys have no financial risk.
⚡ Reliability
Best When
Your agent needs a developer-friendly, commission-free US equity brokerage with a paper trading environment for safe iteration before live execution.
Avoid When
You need options chains, international markets, or institutional-grade execution algorithms.
Use Cases
- • Build and backtest equity trading algorithms in paper trading mode before going live with identical API calls
- • Execute fractional share orders for portfolio rebalancing agents that need precise dollar-based allocation
- • Stream real-time trade and quote data via WebSocket for price signal agents without paying for a separate market data subscription
- • Manage multi-account portfolios through the Broker API for fintech apps serving end-user investors
- • Implement automated tax-loss harvesting by querying positions and placing replacement trades within wash-sale windows
Not For
- • Options or futures trading — Alpaca only supports equities and crypto spot
- • International stocks or forex — US-listed securities only
- • Institutional prime brokerage with DMA, dark pool, or algorithmic execution routing requirements
Interface
Authentication
API key ID + secret for direct account access; OAuth2 for Broker API apps acting on behalf of end users. Paper and live trading use separate key pairs — switching environments requires swapping credentials.
Pricing
Trading is commission-free. Market data is tiered — free IEX feed is delayed/limited vs paid SIP consolidated tape. Funded brokerage account required for live trading.
Agent Metadata
Known Gotchas
- ⚠ Paper and live environments use different base URLs and separate API key pairs — accidentally submitting live orders to paper env (or vice versa) is a common agent misconfiguration
- ⚠ Market hours enforcement: orders placed outside regular hours require extended_hours: true or they queue silently until open, causing unexpected execution timing
- ⚠ Fractional shares have minimum order sizes ($1 notional or 0.001 shares) that differ from whole-share lot size rules — agents must check asset fractionability before order construction
- ⚠ Position quantity after a partial fill updates immediately but buying power updates may lag by 1-2 seconds — agents polling account state rapidly may see stale values
- ⚠ WebSocket data stream uses a different authentication handshake than REST — auth message must be sent as the first frame after connection or the stream delivers no data without error
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for Alpaca Markets API.
Scores are editorial opinions as of 2026-03-06.