overtyping

Overtyping, also called overstrike or replace mode, is a text editing behavior in which typed characters replace existing characters at the cursor rather than being inserted to the right. In most modern word processors and many code editors, the default mode is insertion, so new text shifts the existing text to the right. Overtyping is therefore a mode that some users encounter when a toggle called overtype, overwrite, or replace is switched on.

Historically, overtyping was common on early typewriters and line editors where screen width and hardware constraints made insertion expensive or impossible. Some early word processors and terminals offered a dedicated overtype mode to quickly correct single-character mistakes without reflow. In contemporary software, overtyping persists as a mode or command in some editors, notably vim (replace mode) and various editors that expose an Insert/Overwrite toggle. Modern users often encounter it as a transient setting that can be turned off.

In practice, overtyping works by replacing the character under the cursor with the newly typed character. If there is more text after the cursor, it remains unchanged, and the cursor advances by one position. If the end of the line or document is reached, behavior depends on the editor: in many editors it will overwrite the last character or extend the line, sometimes temporarily adding spaces to preserve alignment.

The main implication of overtyping is the risk of accidental data loss or corruption when text is replaced unintentionally. To avoid this, users can switch to insertion mode, disable overtype in preferences, or use undo after an incorrect overwrite. In some editors, pressing the Insert key toggles the mode.