How to Prefill a Signup Form With User Information - SMASHSEND

> **Availability:** field prefilling is rolling out. The URL format below is the one it will use, so links you build now keep working once it is live. If you already know who someone is, you should not make them type it again. You can pass values into a SmashSend form through the URL, and the matching fields are filled in before the person sees the form. ## The URL format Add a query parameter for each field you want to fill. The parameter name is the **field key**, which you can find next to each field in the form builder. ```https://form.smashsend.com/f/YOUR_FORM_KEY?email=jane@acme.com&name=Jane``` Anything you do not pass is simply left blank. The person can still edit a prefilled field before submitting. ## Encode your values Query strings cannot contain raw spaces, ampersands or plus signs, so URL-encode every value you interpolate. In JavaScript: ```const url = new URL("https://form.smashsend.com/f/YOUR_FORM_KEY"); url.searchParams.set("email", user.email);url.searchParams.set("name", user.fullName); // searchParams.set encodes for you, so spaces and symbols are safe.window.location.href = url.toString();``` ## Prefill from an email Inside a SmashSend email you can build the link with contact properties, so each recipient gets their own prefilled form: ```<a href="https://form.smashsend.com/f/YOUR_FORM_KEY?email={{contact.email}}">  Complete your details</a>``` ## Reserved parameters Two parameter names are reserved and are not treated as fields: -   `ref` tracks who referred this signup. It is set automatically on the share links your referrers get, so do not overwrite it.-   `password` unlocks a password-protected form. If one of your own fields uses a reserved key, rename the field key in the builder to avoid the clash. ## A word on trust Anything in a URL can be edited by the person opening it, so treat prefilled values as a convenience rather than as verified data. If you need to be certain who submitted a form, confirm it on your side, or turn on double opt-in so the email address has to be verified. ## Have questions? If you get stuck, email [support@smashsend.com](mailto:support@smashsend.com) or [contact us](https://smashsend.com/contact).