Best APIs for Algorithmic Trading Agents in 2026
A practical comparison of trading data APIs for AI agents. Prices, sentiment, technicals, screeners, and intelligence — what each API offers and what it costs.
If you're building an AI trading agent in 2026, you need data: prices, sentiment, technicals, fundamentals, and economic indicators. The question is whether you cobble together 3-4 APIs or use one that covers everything.
Here's a practical comparison of the major options, what they actually offer, and what they cost.
The Contenders
Alpha Vantage
The incumbent. Good OHLCV data and 50+ technical indicators. No sentiment, no screener, no intelligence. Free tier is 25 calls/day with 15-minute delayed prices.
Finnhub
Real-time prices and WebSocket streaming. Good for pure price data. Limited sentiment, no screener, no backtesting. Free tier is generous at 60 calls/min.
Polygon.io
Exchange-direct data, excellent for tick-level precision. Expensive ($29+/mo for delayed, $199+ for real-time). No sentiment or intelligence layer.
Polaris
Intelligence + market data in one API. Prices, 20 technical indicators, NLP screener, sentiment scoring, backtesting, forex, commodities, crypto, economic data. Free tier: 1,000 credits/month.
Feature Comparison
| Feature | Polaris | Alpha Vantage | Finnhub |
|---|---|---|---|
| Live prices | 15s cache | 15min delayed (free) | Real-time |
| Technical indicators | 20 + signals | 50+ | Limited |
| NLP screener | Yes | No | No |
| Sentiment scoring | -1.0 to +1.0 | Basic label | Basic |
| Backtesting | Yes | No | No |
| Claim verification | Yes | No | No |
| Bias detection | Yes | No | No |
| Forex + Commodities | Yes | Yes (separate key) | Yes |
| Crypto (200 tokens) | Yes | Limited | Yes |
| Economic data (FRED) | Yes | Yes (separate key) | No |
| Free tier | 1,000 credits/mo | 25 calls/day | 60/min |
The Intelligence Gap
The biggest difference isn't price data — everyone has that. It's what sits on top of it. When your agent reads “Oil prices rise on Middle East tensions,” can it tell you:
- • How confident is this claim? (confidence score)
- • Are different outlets framing it differently? (bias detection)
- • What's the counter-argument? (counter-arguments)
- • Which tickers are correlated? (sector correlations)
- • Has this brief actually moved the stock before? (news impact)
No other trading API answers these questions. That's the intelligence layer.