A social network built around the text-message envelope
In 2006, a phone text was not simply a short email. SMS—the system that carries text messages between mobile phones—typically allowed 160 characters in one message. Twitter’s early design had to fit into that small envelope if people were to post from basic phones, not just from a web browser.
That made the character limit a practical product constraint. A post sent by text had to leave room for the service to identify the account sending it. Twitter set aside 20 characters for that information, leaving 140 for the message itself.
Why not split longer posts into several texts?
SMS can handle longer messages by breaking them into pieces, but that adds friction: the phone and network must divide the text, send the parts, and reassemble them. Depending on the device or carrier, a long message could also be delivered as multiple messages. Keeping each post within one SMS made the basic interaction simpler and more predictable.
The limit also shaped what Twitter felt like. A thought had to fit in a compact burst; extra context often meant editing, replying, or sending another post. The constraint was not just a number on a screen—it reflected the communication channel Twitter was designed to work through.
