Formaster by Lu4nScr1pt1ng

Formaster lets you click through a form once, mapping each field to a data generator, and then fill that same form automatically from then on.

Click "Map fields on this page", click each input, hit Finish. Each mapped field gets a generator: built-in ones for CPF, CNPJ, RG, passport, phone numbers, postal codes, city/state/street (Brazil or US), birthdates, passwords, credit cards, or just a fixed value. Most of these have their own options too, like masking, character length, or which country's data to use.

If the built-ins aren't enough, write your own generator in JavaScript. It runs in a sandboxed interpreter with no access to the page or the browser, and can read values from earlier fields in the same run (so a "confirm password" field can just copy whatever "password" generated).

Mappings are saved per site as a script, matched by URL. You can edit them as a normal form or as raw JSON, export/import them, and run them again from the toolbar icon whenever the page matches.

There's also a Playground page bundled with the extension, a demo form with every field type, so you can try mapping and generators without needing a real site.

Nothing is sent anywhere. Everything stays in the browser's local storage.