Mode error
A mistake caused by doing the right action in the wrong interface mode, like typing with Caps Lock on or drawing with the wrong tool active.
See it
What it is
A mode error happens when the same input means different things in different interface states and the user acts as if the other state were active. Typing with Caps Lock on is the everyday version; drawing on the wrong layer or clicking with a crop tool still selected can waste much more than a line of text. Vim makes the trap explicit with normal and insert modes, and even fluent users still type a whole sentence in normal mode and watch it execute as a string of commands. Larry Tesler spent a career fighting exactly this: his slogan was 'Don't Mode Me In' and his car's license plate read NOMODES.
Avoid persistent modes when a temporary action or explicit command will do. When modes are necessary, make the active one impossible to miss, change the pointer or surrounding controls with it, show what the next action will do, and provide a fast route back to the neutral state.
The gotcha is a tiny toolbar highlight that asks peripheral vision to protect the work. People focus on the canvas, not the mode switch. Put status near the action area, reset one-shot tools after use where that matches expectations, and make unintended results immediately undoable.
Ask AI for it
Reduce mode errors in this editor. Keep the active tool visible beside the canvas, mark its toolbar button with aria-pressed='true', update the CSS cursor to match the tool, and show a one-line preview of what the next click will do. Let Escape return to the neutral Select tool, reset single-use tools immediately after they run, and never reuse the same keyboard shortcut for different actions without an equally visible mode label. Record each edit in the Command pattern so Ctrl+Z and Cmd+Z can reverse an action performed in the wrong mode.