This list is a complement to awesome public datasets, a list of datasets that provide a streaming interface, typically via WebSockets.

The list includes both free APIs, and those which you have to pay to use - 💰

• Coinbase - Coinbase provides a free market data fee; giving access to real-time price updates, level 2 data, orders and matches. This is a high frequency feed with hundreds of events each second.
• Bitquery.io - Bitquery provides blockchain data, offering real-time streaming APIs for 40+ chains, NFT APIs, and a money flow investigation tool.
• IEX Trading - IEX was created in response to questionable trading practices that had become widely used across traditional exhcanges! Their API provides streaming Stock market data.
• Blockchain transactions - Provides real-time notifications about new transactions and blocks.
• Open Rail Data - A collection of APIs that provide data relating to the UK rail network, including reference data, train timetables, and live service updates. The live data is streamed using the STOMP protocol.
• CoinCap - provides real-time pricing and market activity for over 1,000 cryptocurrencies.
• DexPaprika - DEX data for 36 blockchains via SSE streaming, pushed as swaps land. 36M+ pools, 33M+ tokens. Free tier, no API key required (plans and limits). Streaming docs.
• Finnhub Stock API - Real-Time RESTful APIs and Websocket for Stocks, Currencies, and Crypto.
• CoinCheck - a cryptocurrency API that has a WebSocket interface (in beta)
• 💰 Twitter - Twitter provides a streaming interface for Enterprise clients
• 💰 Saxo Bank OpenAPI - This API provides access to Saxo Bank's trading engine, which includes streaming price feeds.
• EventSim - Program that generates event data for a fake music web site (similar to Spotify).
• 💰 ShadowTraffic - ShadowTraffic provides free and paid editions of a developer tool for generating synthetic streaming data. Mostly useful for stream processing data.
• TikTool Live - Real-time TikTok LIVE stream events (chat, gifts, viewers, battles) via WebSocket. Free tier: 50 req/day.
• 💰 Live Tennis API - WebSocket push feed for live tennis across ATP, WTA, Challenger and ITF: every point as it happens, with the scoreline, who is serving and match events. Speaks the Centrifugo client protocol rather than plain JSON frames. Streaming is a paid tier; the REST live-score endpoint has a free tier (100 calls/day, no card).
• Helium MCP - Free REST + MCP API combining ML-derived options pricing (fair value, prob_ITM, Greeks) with structured news intelligence (3.2M+ articles, 31-dimension bias scoring). 10 endpoints, JSON in/out, 50 free queries per IP. Source.