Doublegram Captcha for groups

An open Telegram group attracts spammers quickly. You barely reach a hundred members before links to casinos and "easy income" start flying through the chat. Doublegram Captcha takes over the first line of defense: a newcomer passes a check before getting the right to write. 🛡

Check first, speak later

The scheme is simple. When a new member joins, the bot temporarily restricts their rights and asks them to complete a captcha. Prove you are human and you get access. Fail, and you are removed automatically.

An admin does not have to watch arrivals or ban people by hand. The bot works around the clock while you sleep or do other things.

What the protection is made of

The developers describe several layers that work together:

• Telegram signature. A built-in authenticity check of the user through the messenger itself.
• reCAPTCHA v2. A familiar human-or-bot test that usually runs quietly in the background by analyzing behavior.
• The service's own anti-spam algorithms that filter out suspicious accounts.

The check opens as a mini app inside Telegram, so people do not have to visit outside sites.

Set it up in five steps

1. Add the bot to your group.
2. Make it an administrator.
3. Grant the right to restrict members. Without it the bot cannot mute a newcomer.
4. Open the main menu with /start and choose your options.
5. Ask a friend to join through an invite link and see what the check looks like.

The last step is optional but saves nerves: you instantly see what a new member sees.

A firewall for your group

The bot's second command, /firewall, opens filtering rules. According to the service website, that includes geographic blocking. It helps if your community speaks one language and you regularly get waves of joins from regions you do not care about.

Turn rules on carefully. A filter that is too strict can keep out ordinary people, for example those who connect through a network in another country.

What a captcha cannot do

A captcha guards the door but does not watch what happens inside. If a spammer passes the check by hand, or an account was already in the group, the bot will not stop them. Full moderation needs separate tools: rules, word filters, limits for new members.

Treat Doublegram Captcha as an entrance filter, not as your whole order system. 👍

Who benefits

• Admins of open chats and hobby communities.
• Owners of groups tied to channels with lots of comments.
• People who are regularly hit by fake accounts.

For closed groups where you add people by hand, a captcha is hardly needed. For everyone else it removes most of the junk before the first message.