Invalid input is an admirably brief error message. It tells you that something has displeased the form while revealing almost nothing about how to restore the relationship.
We can do better.
Form validation should help someone finish a task correctly. That means explaining the requirement, identifying the problem and providing a workable route back. The red border is useful supporting cast, but it shouldn’t have to deliver the entire scene.
Start by asking whether the rule needs to exist
Say someone is sending an inquiry through a fictional service website. They enter a phone number with spaces. The form expects a different format and rejects it after submission.
First, ask whether the restriction is necessary. Can the application accept common formatting and normalize it safely? A rule that exists only because the developer’s first test value had no spaces may be creating work for everybody else.
If a format genuinely matters, show an understandable example before the error occurs. Keep the field label visible and connect any instructions appropriately for assistive technology.
Sandrina Pereira’s accessible-validation guidance explains why a visible message alone isn’t enough.1 A screen-reader user needs to discover which field is invalid and understand its associated explanation too.
Slow pages and outdated forms were holding Office Accomplice back. See how the redesign fixed both.
Point out problems at a helpful moment
Timing matters as well. An email field can look incomplete while somebody is still typing an email address. Announcing an error after the first letter is like interrupting a sentence to point out that it hasn’t ended yet.
Choose validation timing according to the task and check the experience with actual input. On submission, help the person locate the errors. For a longer form, an understandable error summary with routes to affected fields may help, alongside the field-level messages.
Keep the person’s work and explain the next step
Preserve the answers that are safe and appropriate to retain. Clearing an entire inquiry because one value needs attention is a surprisingly thorough punishment for a minor misunderstanding.
The message itself should explain what happened and what to do next. A phone field that needs an area code can say so. A request that failed because the service is unavailable should not accuse the person’s phone number.
That distinction also affects recovery. Correcting input and trying again after a temporary system failure are different actions. Staff may need a way to investigate the latter without asking the customer to reconstruct everything.
Baymard’s form-design work provides established context for clear labels, manageable layouts and helpful feedback.3 Don’t borrow a later conversion statistic to justify a particular fix. Watch whether people can complete the relevant form.
Related read: Does this really need a popup?
Test the route back to a finished form
I’d test the awkward route deliberately: submit a missing value, fix it by keyboard, submit again and confirm that the successful result is clear. Repeat with the relevant assistive-technology checks.
It helps to look beyond the field too. Kate Kaplan’s distinction between user flows and wider journeys reminds us that the person may be trying to arrange a service, not simply pass a validation test.2 The confirmation and follow-up need to support that larger purpose.
We can be friendly without making an error message perform stand-up. Plain wording, preserved effort and a clear next step are often the warmest choices.
Let the person know what needs attention and help them continue. The form is there to receive an inquiry, not award a certificate in guessing its preferred punctuation.