Choosing a market-data API is one of the first architectural decisions you make when building a trading or markets app. It's also one of the easiest to get wrong. The landscape is fragmented: providers specialize in different asset classes, pricing models vary widely, and the gap between "works for a demo" and "works in production" is wider than most developers expect.
This guide compares the major market-data API options across what actually matters: data freshness, asset coverage, real-time delivery, developer experience, and cost. There's no single best API for every project, but there is a clear winner for most production use cases.
What We're Comparing (and Why It Matters)
Not all market-data APIs do the same thing. Here's what we're evaluating.
- Data freshness / latency. How old is the data when it reaches your app? Ranges from sub-second to 15-minute delayed. Fine for a watchlist; dangerous for a trading screen.
- Asset coverage. Stocks and ETFs are table stakes. Options chains, crypto, and prediction-market (event) contracts are where providers diverge. Your users will ask for all of them eventually.
- Enrichment. Raw ticks vs production-ready data (consolidated quotes, OHLCV bars, corporate actions, options greeks). If the API only gives you raw prints, you're building the rest yourself.
- Real-time delivery. WebSocket subscriptions and webhooks vs REST polling. Polling is fine for slow-moving data; live quotes and trade streams need push-based delivery.
- Cost and free tier. Some providers meter by request, some by symbol, some gate real-time behind exchange agreements. A "generous" free tier that excludes the data you need isn't generous.
- Developer experience. SDKs, documentation, REST vs GraphQL, and how fast you get from an API key to working code.
The Contenders
Elgon is a REST market-data API covering US stocks, ETFs, and crypto, plus sandbox-simulated options and prediction markets, through one endpoint. Plain HTTP GET (no GraphQL, no WebSocket), with real but delayed quotes and a signed, timestamped receipt on every response you can verify yourself. Elgon is an independent project, not affiliated with Robinhood. Built for dashboards, screeners, and watch-and-alert apps.
Polygon.io is a developer-focused market-data provider covering US stocks, options, forex, and crypto, with real-time and historical REST and WebSocket APIs. A common default for equities-first projects.
Alpha Vantage is a broad, budget-friendly API covering stocks, ETFs, forex, and crypto, plus a large library of technical indicators. Simple REST interface. A popular first API for prototypes and hobby projects.
Twelve Data covers stocks, forex, crypto, and ETFs with real-time and historical REST and WebSocket endpoints. Clean docs and a credit-based pricing model.
Finnhub pairs market data with fundamentals, estimates, and alternative datasets across global equities. Strong on company data, useful for research and analytics tools.
Alpaca is a brokerage-first platform whose market-data API ships alongside execution. Convenient if you plan to route orders through Alpaca, and a solid data source for US equities and crypto.
IEX Cloud is a flexible equities and fundamentals API known for a clean developer experience and usage-based pricing.
Head-to-Head Comparison Table
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| Feature | Elgon | Polygon.io | Alpha Vantage | Twelve Data | Finnhub |
|---|---|---|---|---|---|
| Stocks & ETFs | Yes | Yes | Yes | Yes | Yes |
| Options chains | Yes (sandbox) | Yes | Limited | Limited | Limited |
| Crypto | Yes | Yes | Yes | Yes | Yes |
| Prediction markets | Yes (sandbox) | No | No | No | No |
| Real-time (WebSocket) | No (REST, delayed) | Yes | No | Yes | Yes |
| OHLCV bars | No | Yes | Yes | Yes | Yes |
| Corporate actions | No | Yes | Limited | Limited | Yes |
| Signed data receipts | Yes | No | No | No | No |
| API style | REST | REST + WS | REST | REST + WS | REST + WS |
| Free tier | Yes | Yes | Yes | Yes | Yes |
Note: Provider features and pricing change frequently. Verify current plans on each provider's site before making a decision.
Best Market-Data API by Use Case
The right API depends on what you're building.
Building a dashboard, screener, or watch-and-alert bot
Best choice: Elgon
These tools react on the scale of seconds to minutes, so real but delayed quotes are the right fit — and that is exactly what Elgon serves over REST, with a signed, timestamped receipt on every response so you can prove what a price was and when you received it. Note the flip side: latency-sensitive trading needs sub-second, real-time feeds, and Elgon is not that. For a live order screen, use a specialized low-latency feed instead.
Basic quotes for a watchlist or portfolio tracker
Best choice: Alpha Vantage
If you need end-of-day or lightly delayed quotes for established symbols and can tolerate simple REST polling, Alpha Vantage is the easiest starting point. Broad coverage, a large indicator library, and a free tier that's good enough for a personal tracker.
Equities-first app that needs options too
Best choice: Polygon.io or Elgon
Both cover US stocks and full options chains with real-time and historical data. Choose Polygon.io if you want an equities-focused provider; choose Elgon if you also want crypto and prediction markets, plus signed data receipts, through the same API.
Fundamentals and research
Best choice: Finnhub
Finnhub is strong on company fundamentals, estimates, and alternative datasets. If your product is a research or analytics tool rather than a live trading screen, its breadth of company data is a good fit. Pair it with a real-time provider for live quotes.
You also need execution
Best choice: Alpaca
If you plan to route orders through a broker, Alpaca's data ships alongside execution, which simplifies your stack. Just know that if you later need options, prediction markets, or verifiable data receipts, you'll want a dedicated data API alongside it.
The Hidden Costs Most Developers Miss
The sticker price of a market-data API is often the smallest part of the total cost. Here's what actually gets expensive.
Raw prints require an enrichment layer
If you pick a provider that only streams raw trades and quotes, you're getting market data, not product-ready data. Going from "here's a print" to "this is the consolidated best bid/offer, split-adjusted, with a VWAP and a candle" means building consolidation, corporate-action handling, and aggregation yourself — and maintaining it as venues change. Unless market-data processing is your core product, building that is a distraction.
Cheap, delayed data costs you in stale prices
Free and low-cost tiers are frequently delayed by minutes. For a watchlist that's fine. For anything that triggers an action — an alert, an order, a hedge — acting on a stale price can cost far more than a year of API fees.
Multiple providers means multiple problems
Using one API for equities, another for options, and a third for crypto means three data formats, three billing systems, three sets of rate limits, and three points of failure. Teams that once stitched several providers together increasingly consolidate onto a single market-data API to simplify debugging, billing, and correctness.
Our Recommendation
For basic quotes on a budget, Alpha Vantage is a fine starting point. If it solves your problem, use it.
For anything production-grade — trading platforms, portfolio tools, options screeners, bots, analytics — Elgon gives you enriched data across stocks, ETFs, options, crypto, and prediction markets at trading-grade speed, through one API, with signed data receipts you can verify. That's the difference between a demo and a product.
FAQ
What is the best free market-data API for developers?
For basic quotes and prototyping, Alpha Vantage's free tier covers most needs across stocks, ETFs, forex, and crypto. For real-time, enriched data — consolidated quotes, OHLCV bars, options chains, and streaming — Elgon's free tier provides significantly more depth through a single endpoint.
What is the best API for real-time market data?
Elgon serves real but delayed quotes over REST for stocks, ETFs, and crypto (options and predictions are sandbox-simulated), with a signed receipt on every response — it is not a real-time or WebSocket feed. If you need true sub-second data, Polygon.io, Twelve Data, and Finnhub offer WebSocket streaming for their covered asset classes; Alpha Vantage, like Elgon, is REST and better suited to delayed use cases.
How much does a market-data API cost?
Costs vary by provider, asset class, and whether you need real-time exchange data (which often carries separate exchange fees). Most providers offer a free tier and scale on usage. The real cost is often not the API itself — it's the engineering time to enrich raw prints into production-ready data if you choose a raw provider.
What is the difference between a market-data API and a broker API?
A broker API (such as Alpaca or a brokerage's own endpoints) lets you place and manage orders and read account state. A market-data API (Elgon, Polygon.io, Alpha Vantage) delivers quotes, bars, options chains, and analytics for the whole market, whether or not you trade through a specific broker. Many production apps use both: a broker API for execution and a data API for everything users see on screen. For more, see our explainer on what a market-data pipeline is.
Is Alpha Vantage better than Twelve Data?
It depends on your needs. Alpha Vantage has a large technical-indicator library and a simple REST interface, which is convenient for prototypes. Twelve Data adds WebSocket streaming and a credit-based model that can be more flexible at scale. See our full Alpha Vantage vs Twelve Data comparison for a detailed breakdown.
Try Elgon free at elgonrpc.xyz. One API for stocks, ETFs, options, crypto, and prediction markets — with signed, timestamped data receipts you can verify.