Does Telegram have a captcha for new group members?

No check of this kind comes with the group. You get invite links with admin approval, slow mode and default permissions, but none of them tests a new member on its own. A bot such as @GroupGateProBot adds the test.

What happens to a member who does not tap?

After 5 minutes, or 10 with Pro, the bot removes the member with a ban of 60 seconds and deletes the card. The member can join again later.

Which admin rights does the bot need?

Ban users and Delete messages. The add button on this page asks for both. Without them the bot cannot mute or remove a member.

Yes. The check, the 5-minute window and your own welcome text are free. Pro is optional, 150 Stars one time for one group.

How to Stop Spam Bots Joining a Telegram Group with a Captcha

A public Telegram group attracts accounts that join, post a link and leave. Most of them are scripts. They do not read the welcome message, and they do not answer a question. A check that asks the new member to do one thing before they can write stops a large part of them, at no cost to real people.

Telegram itself gives you invite links with admin approval, slow mode and the default permissions of members. None of these checks a new member on its own: approval needs an admin every time, and slow mode only spaces the posts. @GroupGateProBot adds the missing step. It mutes each new member, posts a card with one button, I'm human, and removes the member if the button is not tapped in time.

This guide shows how to set it up, what a new member sees, and what the check does not do.

Keep reading

Steps

Add the bot to the group as an admin. Use the button on this page. It asks for the two rights the bot needs: Ban users and Delete messages. Without them the bot cannot mute or remove a member. You can also add @GroupGateProBot from its profile and set the rights yourself.
Send /gate in the group. The bot answers with the status of the check, which should read on, and the time a new member has to tap. Only group admins can use the command. /gate off switches the check off and /gate on switches it on again.
Write your welcome text with /welcome. Send /welcome followed by your text, 500 characters at most. {name} becomes the name of the new member. For example: /welcome Hello {name}, tap the button to start chatting. Your own welcome text is free. Without it the bot uses a default text.
Watch what a new member sees. When someone joins, the bot mutes them and posts the welcome card with one button, I'm human. Only that member can tap it, and a tap lifts the mute at once. Another member who taps gets a note that the button is not for them.
Test with a second account. Join the group from another account. Check that the card appears, that you cannot write before the tap, and that you can write after it. Leave the second account without tapping once, to see the removal.
Decide on Pro for the link filter. A tap proves very little about a person who is determined to spam, so a spammer who taps may post a link right away. The link filter, part of Pro, deletes links and @-mentions from members who joined less than 24 hours ago. Switch it with /links on or /links off.

Good to know

Each new member has 5 minutes to tap the button, or 10 minutes with Pro. With no tap the member is removed with a ban of 60 seconds, which lets them join again. It is not a permanent ban.
This is a button check, not a puzzle. A script that clicks buttons passes it, and so does a human spammer. The check works against accounts that join and never act, and it adds a pause before anyone can post.
Pro is per group and optional: 150 Telegram Stars, one time. It gives a 10-minute tap window, one button of your own with up to 40 characters of text instead of the button of the bot, and the link filter.
The link filter bans and mutes nobody and admins are exempt. It deletes a message only when it holds a link or an @-mention and the author joined less than 24 hours ago. It is the only part of the bot that looks at message text, and it does not store the text.
The bot works in groups with topics. The card appears in the topic where the join message shows. If that topic is closed, the bot unmutes the new member instead of leaving them stuck.
Members who were already in the group before you added the bot are not checked.

Add to a group See GroupGateProBot About the bot

FAQ

Does Telegram have a captcha for new group members?: No check of this kind comes with the group. You get invite links with admin approval, slow mode and default permissions, but none of them tests a new member on its own. A bot such as @GroupGateProBot adds the test.
What happens to a member who does not tap?: After 5 minutes, or 10 with Pro, the bot removes the member with a ban of 60 seconds and deletes the card. The member can join again later.
Which admin rights does the bot need?: Ban users and Delete messages. The add button on this page asks for both. Without them the bot cannot mute or remove a member.
Is it free?: Yes. The check, the 5-minute window and your own welcome text are free. Pro is optional, 150 Stars one time for one group.

Related guides

Related bots

GroupGateProBot — Mutes each new member until they tap a button, and removes accounts that never tap.
AnonInboxProBot — A personal link where strangers write to you anonymously; you reply and can block.
AnonSayProBot — Post anonymously into a Telegram group through the bot.
JoinApproveProBot — Approves every join request at once and sends each new member one welcome message.

Curious what the Pro features cost? See pricing.