errors

A dialog that interrupts the flow to demand acknowledgement or confirmation of a consequential action before anything else can continue.

A modal that stops an action part way through to ask whether you meant it, naming the consequence in its confirm button rather than saying OK.

The line attached to a field that says what went wrong and what to do about it, announced to assistive technology the moment it appears.

Content moving after it has already been painted, usually because something arriving late took space that was never reserved for it.

Persisting the reader's work continuously without a save action, usually with a quiet status line reporting when the last save happened.

A review screen listing everything the reader entered, with a change link beside each answer, shown before the submission is final.

Offering a corrected spelling for a query that returned little or nothing, either as a suggestion to accept or as a substitution the reader can undo.

The whole screen a site serves instead of the page that was asked for: what happened, in the reader's words, and the shortest way back to something that works.

A block at the top of a failed form listing every problem as links that move focus to the field that caused it.

A page that looks finished at a point where content actually continues, so the reader stops scrolling and never sees the rest.

Accepting whatever shape the reader types and normalising it afterwards, instead of rejecting input that differs only in spacing or punctuation.

Checking a field as the reader fills or leaves it and showing the verdict beside that field, rather than saving every complaint for the submit button.

What a search or filtered list shows when nothing matched, naming the query, explaining why, and offering a way to loosen the constraints.

A burst of repeated clicks on one spot, the shape frustration takes when a control answers nothing, and the analytics signal that goes looking for it.

Overriding the browser's scrolling so a wheel turn advances a scripted sequence instead of moving the page by the distance the reader asked for.

Removing an item from view but keeping it recoverable in a trash or archive for a period, so deletion is reversible without a confirmation step.

Guarding a destructive action by making the reader type the name of the thing being destroyed before the confirm button becomes usable.

Letting an action run immediately and offering to reverse it afterwards, instead of stopping to ask whether the reader really meant it.

Warning the reader that edits will be lost before a navigation or close is allowed to proceed, and offering to save or discard first.

A stray click the browser emits after a touch has already been handled, landing on whatever moved under the finger in the meantime.

Requiring a press to be held for a moment before a destructive action commits, with progress shown so the wait is understood as deliberate.

Physically shaking a device to trigger undo or redo, an accelerometer gesture Apple defines system wide for reversing a recent edit.

A hover style that stays applied on a touch device after a tap, because there is no pointer to leave and clear the state.

Visible stutter in motion caused by frames arriving late or not at all, so an animation that should be continuous reads as juddering.

Reading a geometric value after writing to the DOM in the same frame, forcing the browser to lay out synchronously over and over and stalling the animation that caused it.

A short lateral wobble used to reject an input, borrowed from the head shake and read as no rather than as an error message.

A bold or italic the browser fakes by smearing or shearing the regular weight, because the real style was never loaded.

The empty rectangle a font renders when it has no glyph for a character, named for the block of bean curd it resembles.

The moment a page paints in the wrong theme before the stored preference is applied, showing a light flash to a reader who chose dark.

The small fixed set of colours a product reserves for outcome, typically success, warning, danger and info, so meaning is consistent wherever it appears.

Naming the field that failed and saying what went wrong in text, rather than only outlining the input in red.

An element hidden from assistive technology that is still in the tab sequence, so keyboard focus lands on something a screen reader refuses to describe.

The programmatic mark that a field's value failed validation, paired with a pointer to the message that explains it.

A place keyboard focus can enter but not leave by keyboard alone, stranding anyone who is not using a pointer.

A focusable control placed inside another control, such as a button inside a link or a checkbox inside a clickable row, which garbles the announcement and can leave the inner control unreachable.

Activating a control on pointer release rather than press, so someone who lands on the wrong target can slide off and abort.

Using tabindex values above zero to force an order, which yanks those elements to the front of the whole page sequence and is almost always a bug.

A warning before a session or form expires with a simple way to extend it, so a slower reader does not lose their work silently.