Goal Seek answers the backwards question a spreadsheet cannot: you know what the answer should be, and you need to know what to put in. What interest rate makes this payment 1,500? What price makes this margin 30%? How many units make this break even?
Excel has had this since the 1990s. Google Sheets™ has no equivalent anywhere in its menus, so the job falls to add-ons — and the one most people found is rated 2.8 stars across 331 reviews. Its users say the same four things: it throws an error when the panel opens, a simple loan calculation takes over twenty seconds, it never remembers the cells you were already on, and when it fails it does not say why.
So this one is built around those four complaints. The search is a bracketing pass followed by Brent's method, which typically needs eight to twelve recalculations instead of hundreds — and since every recalculation is a round trip to Google's servers, that is the speed. The form opens filled in from the cell you have selected. Every failure names its cause. And if anything goes wrong at any point, your sheet is put back exactly as it was.
One thing it cannot do, said plainly: give you a keyboard shortcut. In Excel you press Alt + A, W, G. Google Workspace™ add-ons are not allowed to bind keys — no add-on can, whatever its listing says. You open the side panel from the right-hand rail.
That is how goal seeking works, in every spreadsheet program: the input cell must hold a plain number, because the search writes numbers into it. If the cell you name contains a formula, this add-on refuses to start rather than destroy it. Excel refuses too. The result is left in the cell when the search succeeds, and the previous value is one click away under Undo.
One permission, the narrowest one there is: “See, edit, create, and delete only the specific Google Sheets™ spreadsheet this application is used in.” It cannot see your Google Drive™, your other files, your mail or your contacts.
Everything runs inside your own Google account, on Google Apps Script™. Nothing from your file is ever sent anywhere: there is no database and no analytics. Without a licence key the add-on makes no network request at all; with a Pro licence it asks our licence server once a day whether that key is still active, sending only the key and a random identifier for the installation. We could not read your spreadsheet if we wanted to.
Free, forever: the search itself with no limit on how often you use it, the optional search range, the undo button, and the full explanation of every failure. Those are safety, and safety is not for sale.
Pro adds capacity, not correctness: running the same goal down a whole table of scenarios, and saving setups you reuse. See Pro.