There are two kinds of APIs for developers. The Bot API allows you to easily create programs that use Telegram messages for an interface. The Telegram API and TDLib allow you to build your own customized Telegram clients. You are welcome to use both APIs free of charge.
Bot API
Bots are third-party applications that run inside Telegram. Users can interact with bots by sending them messages, commands and inline requests. You control your bots using HTTPS requests to Bot API.
Telegram API and TDLib
Telegram API: This API allows you to build your own customized Telegram clients. It is 100% open for all developers who wish to create Telegram applications.
TDLib: Telegram Database Library (or simply TDLib), a tool for third-party developers that makes it easy to build fast, secure and feature-rich Telegram apps. TDLib takes care of all network implementation details, encryption and local data storage. TDLib supports all Telegram features and makes developing Telegram apps a breeze on any platform. It can be used on Android, iOS, Windows, macOS, Linux and virtually any other system. The library is open source and compatible with virtually any programming language.
