Address autocomplete

An address is the worst-shaped thing a form ever asks for. It has a different number of parts in every country, the parts are named differently, and half of them are ambiguous to the person who lives there. Address autocomplete replaces the interrogation with a single lookup: type a few characters of a street or a postcode, pick a real address out of the suggestions, and the structured fields fill themselves in. Seven decisions become one, and the one that remains is the only one the reader is actually qualified to make.

The machinery is a combobox over an address database, which is worth saying plainly because it means the pattern inherits a solved accessibility problem rather than a new one: a text input, a listbox of suggestions, arrow keys, an active option, and a chosen value announced when it lands. Mention autocomplete is the same machinery aimed at people instead of places, and the difference between them is entirely in what the query is matched against. What address autocomplete adds on top is the fan-out: one selection writes several fields, so the reader has to be able to see what was written and correct it.

That last part is where implementations fail. A lookup that swallows the address into an opaque token leaves anyone with a flat number, a new build, a farm, or a business park with no way to finish, because the database is always a little behind the world. Keep the structured fields on screen after the fill, keep them editable, and keep a plain “enter it manually” path within reach rather than behind an apology. The GOV.UK Design System is unusually blunt about this: a lookup is an optimisation over the manual fields, not a replacement for them.

Two details buy most of the remaining quality. Wait until the query has enough in it to be worth answering, so one character does not return a thousand streets, and say what the field wants before anything has been typed. And reserve the room the suggestion list will take, so opening it never shoves the rest of the form down the page under someone who is mid-sentence.