Bitcoin Index is a Bitcoin realtime price index owned by Coinut. It provides a highly available and robust Bitcoin realtime price index (updated every tens of milliseconds) with free REST and WebSocket APIs access. It is good for merchants or traders to use.
How to use
Get Bitcoin Real Time Price Index
Convert BTC to USD
Convert USD to BTC
Get Realtime Streaming Data
Although you can visit their REST API to get Bitcoin price every few seconds, it would be much better to use WebSocket to achieve high frequency sub-second updates. Simply check out their WebSocket API here: https://github.com/coinut/api/blob/master/bitcoin-index/nodejs/index.js
BitcoinIndex tries to achieve 99.999% uptime (five-nine availability) so that you can use the service nearly all the time. Their backend servers are located in different continents to ensure that the service will not be interrupted by regional network outage, and at the same time, they ensure strong consistency of the data between those replicated servers so no matter where you visit their service, you will get exactly the same result.