"Real-time" is the most abused phrase in market data. Some APIs mean actual exchange-fed live quotes; others mean fifteen-minute-delayed data with a fast response time. Before comparing providers, be precise about the need: a trading system needs true tick-level feeds; a research platform, portfolio tracker, or AI agent usually needs accurate quotes delivered in milliseconds — with delayed data being perfectly acceptable at a fraction of the licensing cost.
1. Eulerpool API — Best for Research, Apps, and AI Workloads
The Eulerpool API delivers quotes for global equities, ETFs, crypto, forex, and commodities at sub-10ms response latency — with delayed market data on free and mid tiers and real-time feeds on Enterprise.
- Global in one namespace: US, European, and Asian equities plus FX, crypto, and commodities — no per-exchange API juggling.
- Beyond the quote: the same API serves intraday candles, historical prices, 52-week analytics, top movers, market breadth, sector performance — and the entire fundamentals layer, so a price never arrives without context.
- AI-ready: quotes and market analytics are exposed through the native MCP server, so ChatGPT and Claude pull live market state directly.
- Honest pricing: free at 100,000 calls/month, production tiers from $99/month, real-time licensing handled cleanly at Enterprise.
2. Polygon.io — Best for US Tick-Level Feeds
For genuine US tick data and websocket streams, Polygon is the benchmark: nanosecond timestamps, full SIP coverage, excellent developer experience. Its scope is its limit — US markets, thin fundamentals. The classic production stack is Polygon for US ticks plus Eulerpool for everything else.
3. Databento
Serious raw exchange feeds with usage-based pricing, aimed at quant desks that want normalized tick data. Overkill — in cost and complexity — for anything short of systematic trading infrastructure.
4. Twelve Data
Decent websocket coverage across asset classes at accessible prices. Latency and depth sit a tier below the leaders.
5. Finnhub
Free real-time US trades via websocket made it popular with hobbyists. Rate limits and data consistency make production use a gamble — see the Finnhub comparison.
Matching the Tool to the Job
- Systematic US trading: Polygon or Databento for the feed — nothing else matters at that layer.
- Apps, dashboards, research platforms, AI agents: Eulerpool — global quotes, millisecond latency, and the full data context in one API.
- Weekend projects: any free tier; upgrade when correctness starts costing money.
Get a free key and benchmark the latency yourself — the numbers are the argument.