HTML Form Validation Tester - check native attributes live.
Paste an HTML form snippet to see which native validation attributes it uses, then test them in a live preview. The checklist reads required, type=email, minlength and pattern on every field. Everything runs in your browser, so nothing is sent anywhere.
Edit the snippet and the checklist and preview update as you type. Scripts in the snippet never run.
Copyable examples
Load one into the editor or copy it into your own page.
required + type=email catches empty and malformed addresses.
required, minlength and a pattern for a phone number.
pattern and minlength enforce a format before the form submits.
Native validation checklist
Supported checks: required, type=email, type=url, type=number, minlength, maxlength, pattern, min and max.
Live preview
Preview only. Submitting here does not send any data.
What does native HTML form validation check?
Native validation is the browser checking a field before the form submits. It needs no JavaScript: the rules live in the HTML attributes. If a field fails, the browser shows its own message and stops the submit until the value is valid.
Native browser validation vs JavaScript validation
Native validation is the first layer and costs nothing: add the attributes and the browser enforces them, including on mobile keyboards and with built-in error messages. JavaScript validation is the second layer. Use it for rules a single attribute cannot express, such as matching two email fields, showing a custom message or validating as the visitor types.
Neither layer replaces server-side validation. A visitor can edit the HTML or post straight to your endpoint, so validate again on the server. For the JavaScript side, read how to validate an HTML form with JavaScript and test patterns with the email regex tester.
HTML form validation FAQ
What does native HTML form validation check?
The browser checks the attributes on each field before the form submits. required blocks an empty value, type=email rejects a malformed address, minlength and maxlength check the number of characters, and pattern tests the value against a regular expression. The browser shows its own message and stops the submit until the field is valid.
What is the difference between native browser validation and JavaScript validation?
Native validation is built into the browser and needs no script: add required, type=email, minlength or pattern and the browser enforces them. JavaScript validation runs your own code, so it can handle cross-field rules, custom messages and live feedback. Native validation is the first layer; JavaScript adds rules the attributes cannot express.
Does native validation replace server-side validation?
No. A visitor can disable JavaScript, edit the HTML or post directly to your endpoint, so the server must validate every submission again. Native and JavaScript validation are for user experience; server-side validation is the security boundary.
Which validation attributes does this tester support?
The checklist reads required, type=email, type=url, type=number, minlength, maxlength, pattern, min and max. The live preview renders the same fields so you can submit it and see the browser's native messages.
Is my form snippet sent anywhere?
No. The snippet is parsed and previewed entirely in your browser. It is never uploaded, stored or sent to splitforms or any other server, and scripts inside the snippet never run.
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