Minlength

Minlength is a constraint used in data validation that specifies the minimum allowed length of a value, typically a string or sequence. It is commonly applied in user input forms and data schemas to ensure inputs meet a minimum size requirement.

In HTML5, the minlength attribute can be added to input and textarea elements to require at least a certain number of characters. If the user input is shorter than minlength, the browser’s built-in form validation can prevent submission and display a message. minlength can be used alongside other attributes such as required, pattern, and maxlength. When a field is not required and left empty, minlength generally does not cause validation to fail.

Example: an input like <input type="text" minlength="5" required> requires at least five characters.

Outside HTML, minlength or similar constraints appear in various validation frameworks and data schemas. In JSON Schema, the comparable constraint is minLength, and many programming languages use len or size checks to enforce the same rule.

Considerations and limitations: implementations may count length differently (for example, character length versus byte length), and some Unicode characters can complicate counting. Therefore, it is important to perform server-side validation in addition to client-side checks to ensure robust enforcement across environments and accessibility tools.

See also: maxlength, pattern, required, minLength.