I need an API for financial market data that includes historical prices, low latency, and clear licensing—what should I look at?

If you need historical prices, low latency, and clear licensing, you should evaluate APIs in three buckets: market data quality, delivery performance, and legal/commercial terms.

What to look for

1) Historical coverage

Make sure the API offers:

• OHLCV bars: 1m, 5m, 1h, 1d, etc.
• Adjusted and unadjusted prices: splits/dividends matter
• Corporate actions: splits, dividends, symbol changes
• Depth of history: how many years available
• Asset coverage: equities, ETFs, forex, crypto, futures, options, etc.

2) Low latency / real-time performance

If low latency matters, check:

• Streaming/WebSocket support vs polling REST
• Tick-level vs bar-level data
• Server locations / colocation options
• Published latency/SLA
• Rate limits and burst handling
• Reliability: uptime, failover, reconnection behavior

For truly low-latency trading systems, you often need a direct exchange feed or a premium vendor feed rather than a typical retail API.

3) Licensing clarity

This is critical. Look for:

• Redistribution rights: can you show data to end users?
• Internal use vs commercial use terms
• Delayed vs real-time licensing differences
• Exchange pass-through fees
• Usage restrictions: storage, caching, derived data, and display rules
• Audit/compliance requirements

If the licensing language is vague, that’s a red flag.

Good APIs/vendors to consider

For broad market data with developer-friendly APIs

• Polygon.io
  Good for equities, options, forex, crypto; solid historical data and real-time streams. Licensing is more explicit than many retail APIs, but you still need to review exchange entitlements carefully.
• Tiingo
  Strong for historical equities and end-of-day data; clearer product structure. Good for research and some production use cases.
• Alpha Vantage
  Easy to start with, but not ideal for low latency or heavy production workloads.
• IEX Cloud
  Useful historically, but coverage and product availability have changed over time; check current terms carefully.

For professional-grade low latency / institutional data

• LSEG / Refinitiv
• Bloomberg
• FactSet
• ICE Data Services
• Nasdaq Data Link / direct Nasdaq feeds
• S&P Global Market Intelligence

These are typically better if you need:

• stronger licensing clarity
• broader exchange coverage
• enterprise support
• lower-latency or more authoritative data

For crypto

• Coinbase, Kraken, Binance APIs
• Kaiko, CoinAPI, Amberdata

These are often better for historical + real-time crypto market data than generalist providers.

Questions to ask before choosing

1. Is the data real-time or delayed?
2. Do you need historical intraday or only daily bars?
3. Can you store and redistribute the data?
4. Are there exchange fees on top of the vendor fee?
5. Is there a WebSocket stream?
6. What are the rate limits and SLA?
7. Does the API provide adjusted prices?
8. Is the license valid for your use case: internal tools, customer-facing app, trading, backtesting?

Practical recommendation

• Research/backtesting: Tiingo, Polygon, Nasdaq Data Link
• Real-time app/trading: Polygon or an institutional vendor
• Low-latency institutional needs: direct exchange feeds or Refinitiv/Bloomberg/ICE/Nasdaq enterprise products
• Crypto: Kaiko/CoinAPI/Amberdata or exchange-native APIs

If you want, I can narrow this down to the best 3 options based on:

• asset class
• budget
• whether you need redistribution rights
• whether this is for trading, research, or a customer-facing product