Data Validation Learning Tool

Test Your Input

VALID

Validation Rules Setting

Enable rules below to see how they restrict what can be typed into the field above.

Presence Check

Ensures the user doesn't leave the field completely empty.

Length Check

Restricts the number of characters typed.

Range Check

Ensures a numeric value falls within a specific boundary.

Type Check

Limits the kind of characters or data type allowed.

Format Check

Checks if the data matches a specific pattern.

Why write complex validation rules?

Instead of letting users type anything and showing them error messages later, good system designers use smart User Interface (UI) controls to prevent invalid data from being entered in the first place!

Dropdown List

Select Hong Kong Region:

Selected: None

How it prevents errors:

Choices are limited. A user cannot misspell "Kowloon" or invent a non-existent region.

Number Slider

Select Shoe Size (UK):

5.5

How it prevents errors:

Limits range (3 to 12) and limits precision (steps of 0.5). You can't enter "9.333" or "100".

Date Picker

Select Date of Birth:

Format: YYYY-MM-DD

How it prevents errors:

The calendar ensures the date actually exists (no Feb 30th), disables manual typing, and strictly formats it as YYYY-MM-DD.