The article provides an overview of the top cryptocurrency APIs available for developers in 2021, detailing their functionalities, integration capabilities, transaction support, and pricing models. It highlights that these APIs are essential for interacting with Bitcoin and other blockchain projects like Ethereum and Dogecoin, offering features such as wallet integration, transaction processing, and market data tracking. Among the APIs reviewed, BraveNewCoin is noted for streaming price index tickets, CoinAPI for accessing trade data, and Coinbase for its robust wallet and transaction support. The piece also discusses APIs like CoinMarketCap for market analytics, Nexchange for exchanging blockchain pairs, and Bitcointy for chart data and currency conversions. Each API is evaluated based on its special capabilities, popularity, and suitability for specific tasks, emphasizing their utility in various cryptocurrency-related projects.