Сообщение на телефон is a free Chrome add-on developed by Aleksey Shikhov. It falls under the category of Browsers and specifically the subcategory of Add-ons & Tools. This add-on allows users to send messages to WhatsApp users without adding them to their contact list.

With Сообщение на телефон, users can simply highlight a phone number on a webpage and click "Сообщение в WhatsApp" (Message on WhatsApp). If the number is registered on WhatsApp, a chat with that number will open in the web version of WhatsApp. If the number cannot be highlighted, such as on Avito, users can still use the same action without selecting anything, and they will be prompted to enter the number manually.

This add-on is capable of recognizing any format of phone number, including those with spaces, dashes, and other separators. It also supports different variations of the country code, such as +7, 8, or without any prefix. Additionally, it can recognize phone number formats written using alphanumeric characters.

Сообщение на телефон is a useful tool for Chrome users who frequently use WhatsApp and need to send messages quickly without adding contacts. It simplifies the process by allowing users to directly message phone numbers found on webpages. However, it is important to note that this add-on only works with the web version of WhatsApp and not the mobile app.