Validation for prototypes

Craig Abbott
3 min readFeb 19, 2018


A laptop on a desk surrounded by clutter. On the screen is a GOVUK service showing a validation error, which is a red box at the top of the page.

On our Slack channel, validation comes up a lot. Designers often aren’t sure how to make the prototyping kit handle validation. Is it client-side? Is it server-side? How do I edit my routes file?

I made a jQuery plugin a couple of years back. It picked up a data attribute called data-required. It also picked up an error message you passed into data-error. Then, it checked if the input was blank or unchecked. If it was, it would append the error messages and prevent the user from submitting the form.

The plugin went down well. At least, it did, until the GOVUK frontend styles got updated. Since then, a dozen or so people have tried to use the plugin but found it doesn’t work anymore. It’s been sat in my Trello board of to-do’s for the best part of a year.

The thing is, I thought I built the plugin off the back of a user need, and I was happy when people praised my work. But in reality, I think I missed the point. As did everybody that used it.

See, the plugin will throw an error if you don’t fill in a text field or don’t select a radio button. But what are you actually testing here? The whole point of a prototype is to go hand in hand with a given scenario so that you can learn something from it. It’s an experiment, under particular conditions, from which you can draw a conclusion.

When we test validation, we’re testing if users understand what went wrong. Whether the content in the error messages makes sense. To see whether users can fix the problem and progress. Leaving something blank is often so obvious we learn nothing from it at all.

When we test validation, we wan’t to be focussing on the difficult things. The nuances in the policy or process that might make the service behave in a way that the user isn’t anticipating. Is a sort-code and an account number an impossible combination? Does the date of birth make a claimant too old for a particular benefit?

For these scenarios, it’s often easier to force the user to see the error, whether it was their fault or not. The easiest way to do this is to duplicate the page and add the errors to the second one. Hard code them into the HTML. No matter what I do on the first page, I’m always going to hit the second one.

You can pull the information they entered into the first form, and use it to pre-populate the second. You then mess with their input on the field that you’re testing. For example, on the first page they entered an 8 digit account number. But on the second page you play it back 7 digits long. Now, when you throw the error explaining it must be a valid account number, you can see if they understand how to fix it. It’s no longer a binary blank or not blank, you’re actually testing if its valid!

We often over complicate prototypes. I’ve been guilty of this in the past. Sometimes they end up so full of logic they are simply bad production builds. Most of the time putting a blanket catch all on empty fields does nothing but block you from doing demos quickly.

We need to remember to build just enough of a prototype to learn about the user needs for a given scenario.

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