Pass a value when a user starts the bot

Pass a short start parameter into your Telegram bot, read it in BJS, and validate it before using it as a command or referral value.

Use a Telegram start link when a user should arrive with a short value, such as a campaign or product code:

Example · Example 1

https://t.me/YOUR_BOT_USERNAME?start=summer_2026

Replace YOUR_BOT_USERNAME with your bot's username. The /start command receives the supplied value as BJS params.

Read a known campaign value

Create /start, leave Wait for answer off, and use this BJS:

Read a known campaign value · Example 2

if (params === "summer_2026") {
  Bot.sendMessage("Welcome to our summer campaign. Send /help to continue.");
} else {
  Bot.sendMessage("Welcome! Send /help to continue.");
}

Create /help with your next steps. Test a plain /start, the campaign link, and a link containing an unknown value. The unknown value should take the normal welcome path.

Parameter rules

Telegram start parameters support letters, digits, _, and -, with a maximum of 64 characters. See Telegram's deep-linking specification.

Treat the value as user-controlled input. It can be edited or reused; receiving a value is not proof of identity, payment, or permission. Keep credentials out of start links and chat responses. Use an explicit allowlist of supported values when the link selects an action.

For referral handling and attribution, use the referral library guide instead of granting a reward merely because a parameter was present.

If params is empty

Check that the link uses ?start=, that the user completed Telegram's start action, and that you are reading the value in the /start execution. A later command does not automatically inherit the original link parameter. Pass it through options when calling the next handler; save a property only if a future independent message needs the value.