Forms Need Validation

Designing inline validation and error handling

Andrew Coyle
4 min readDec 19, 2016

Inline validation is a method to check the validity of input and give feedback before submission. It significantly enhances the usability and user experience of forms. This article explains inline form validation and error handling design techniques.


An example of inline validation

The easy part of inline validation is the validation part. When an entry is validated, it can be communicated with a simple checkmark. Inline errors are more tricky.

Presenting inline errors

Inline errors should be presented with copy explaining the issue and how to fix it.

It can be presented in many ways including:

Above the field

Below the field


As a tool-tip

When should you provide inline validation and errors?

I have distilled five ways to provide inline validation and errors, each with its trade-offs and limitations. It’s important to address problems early and at their source, but it is easy to make matters worse with an inconsiderate approach.

1. When a user clicks into an input

Immediately showing an error when a user clicks into a field is annoying, misleading, and distracting. It is like the form is yelling at you before you say anything. Talk about a bad relationship… However, this approach can be done well by presenting helper text in place of an explicit error until the error is confirmed, or the entry validated.

2. As a user types

This approach annoys the user until the entry is validated. The user is harassed with each entered character, providing more frustration than help. It is like arguing with someone who is talking over you… However, this method provides helpful feedback on password strength and username availability.

3. Once the user reaches the character requirement

This validation method works for inputs with predictable character lengths like Zip codes, phone numbers, CC numbers, etc. However, this can be problematic for internationalization because the format is not always known.

4. When a user leaves the field

Providing feedback when the user leaves the field is probably the best default behavior because validation occurs after the entry is made explicit. However, it can disrupt a user’s flow because it provides feedback after the user has moved on.

5. When a user pauses

This technique provides feedback when a user pauses, mitigating the annoyance of inline errors as a user types and provides feedback when they pause or exit the input.

It is surprising how many forms don’t employ simple inline validation and error handling, and it is even more surprising how often it is poorly implemented. I hope this article helps you design better web form validation. I would love to hear your helpful techniques.

It takes hours of research and attention to create content like this article. Please give it a few claps to motivate me to keep writing. It’s free for you but means a lot to me.

For more:

Find me on Twitter



Andrew Coyle

Formerly @Flexport @Google @Intuit @HeyHealthcare (YC S19)