Using data validation in Proton Sheets

Data validation in Proton Sheets lets you control what people can enter into a cell by setting specific rules — like allowing only numbers, dropdown options, or checkboxes. It helps keep data accurate, consistent, and error-free across the team, especially when multiple people are working in the same sheet.

This guide shows you how to apply validation rules and use them effectively across your spreadsheet.

• Set up data validation
• Common validation types and use cases
• Example
• What happens when invalid data is entered?
• What next?

Set up data validation

1. Select the cell(s) where you want to apply rules.
2. Go to Data → Data validation.

3. Click Add rule.
4. In the Apply to range field, you’ll see the cell or range you’ve selected, such as =Sheet1!A1:A10. You can type a different range manually, an entire column — like =Sheet1!B:B — or add more ranges.
5. Under Validation rules, you’ll see a list of options depending on the type of data you want to allow. Once you select one, the rule will be immediately applied.

Common validation types and use cases

Each validation type applies different rules depending on the kind of data — like text, numbers, or checkboxes — and helps prevent errors before they happen.

Here are some common examples:

• Dropdown provides a predefined list of options, such as Yes, No, Maybe). It’s useful for status fields, responses, or categories.
• Checkbox turns each cell into a clickable checkbox (TRUE/FALSE). It’s useful for to-do lists, approvals, or completed tasks.
• Number allows only numbers that meet specific conditions, such as greater than, less than, or between. For example, you can allow ratings between 1 and 5.
• Is not empty requires that something (anything) be entered in the cell. It prevents users from skipping required fields like “Client name” or “Due date”.
• Custom formula allows you to use formulas like =ISNUMBER(A2) or =A2>0 to build advanced rules.

Example

You want to apply data validation in a project task tracker. Each row represents a task, with columns like Task name, Owner, Due date, Status, Priority, and Completed. Here’s what you can set up:

• For the Owner column, apply a Dropdown rule with the following options: Alice, Bob, John, Tim, and Diana.
• For the Status column, set a Dropdown rule with the following values: Not started, In progress, Blocked, and Completed.
• For the Priority column, apply a Dropdown rule with the following values: 1, 2, 3, 4, and 5.
• And for the Completed column, set a Checkbox rule.

What happens when invalid data is entered?

If you enter a value that doesn’t meet the validation rule, the cell will show an error icon. When you hover over it, you’ll see a message like Invalid: The cell’s contents violate its validation rules.

What next?

If you’re new to Proton Sheets, check out our getting started guide to learn the basics.