When to Use Telegram Bot API vs Telegram API
Choose the API based on the library and features your bot needs. Developing a bot means creating a program that connects to Telegram servers, receives information (such as incoming messages) and sends instructions (like “reply to that message”). Use this page to understand which official APIs can be used for that.
Use MTProto API (also known as Telegram API) when you need lower-level Telegram access. This is the API through which your mobile or desktop Telegram app connects to the Telegram servers. It is open, meaning that developers can use the API to create their own Telegram apps. The MTProto API is named after the MTProto encryption protocol which the Telegram team developed for their messenger.
Use Telegram Bot API for most ordinary bot work. It is built on top of MTProto API and can only be used for bots.
The Bot API was created to allow developers to write bots using plain HTTP-requests without having to learn the complexities of MTProto. It also has features to make development easier, such as webhooks and built-in HTML/Markdown markup.
Most developers use wrapper libraries rather than plain HTTP-requests anyway. These libraries are available for many programming languages and usually provide friendlier tools for everyday bot development.
In short, you can develop bots with either Telegram API or Bot API.
Choose the library first
Some libraries are built on top of Bot API and some libraries are built on top of Telegram API.
On the one hand, you can find many more libraries for Bot API.
On the other hand, Bot API is a bit more limited. By default, it forbids uploading large files or fetching old messages from chat history (you can check out the comparison table). I prefer always using Telegram API, but honestly there is little difference.
For most bots, choose the library first and treat the API choice as part of that decision. The library page has practical options.
Keep userbots outside regular bot design
Telegram API libraries can also control a user account rather than a bot. Such programs are called userbots. Use them when you want to automate actions that users are allowed to do and bots aren't.
Userbots are used for various purposes, such as updating a user's profile picture with the current time, collecting messages from public groups and channels, and automating repetitive tasks.
We are not covering userbots in Papercraft Book, but Telegram API libraries are helpful if you want to develop one.
WARNING
Although Telegram usually doesn't ban accounts for userbots, you should be careful. Telegram may limit or delete spammer accounts.