Validation of form inputs takes the form contents as they are submitted. If you want to check the content input for specific rules, this must be done before submitting to The HTML5 standard offers some possibilities to specify input rules directly in the HTML source code of your form:

Mandatory fields

Input fields that are mandatory can be provided with the attribute required for this purpose.

<input type="text" name="Your name" required>

Email inputs

Fields in which email addresses are to be entered should be defined as type 'email'. This allows the web browser to check whether the input is a formally valid address before submitting the form.

<input type="email" name="Your email address">

Number input

Fields for the input of numerical values, can be defined as type number. With the attributes min and max it is additionally possible to limit the allowed value range.

<input type="number" min="18" max="99" name="Your age">