On iOS, Telegram supports a URI scheme. This allows all kinds of interactions between other apps and websites.

Example: Sending a message with the text "Hello" to +42333

tg://msg?text=Hello&to=+42333

Note that the `to` parameter will only work if you have that user in your contacts. Otherwise nothing happens when you click the link.

Example: Open a chat by username

tg://resolve?domain=TelegramUserName

Note that you can also use the telegram.me/TelegramUsername link to directly open a chat by username.