SharePoint Document Issues

How to Validate File Size and Extensions in SharePoint Forms

Maira Mehtab Sep 22, 2026 869 views

Question details

The user wants to know how to validate or restrict file sizes and extensions when uploading files to out-of-the-box (OOB) list forms in SharePoint Online.

Product: SharePoint Online
Device & OS: not provided
Scenario: Monitoring or restricting document uploads in SharePoint based on file size and specific file extensions.
Observed behavior: The traditional method using Remote Event Receiver add-ins is no longer supported due to retirement, requiring alternative approaches to monitor or validate files.

Before you start

Ensure you have at least Site Member or Owner permissions to edit the document library views and column settings in your SharePoint Online environment.

Solution 1Recommended

Use Default Name and File Size Columns

Enable the built-in Name and File size columns in your document library view to manually monitor and review uploaded files without requiring custom code.

Since Microsoft has officially retired the Remote Event Receiver add-in for SharePoint Online, you can no longer use it for out-of-the-box custom file validation. The most straightforward workaround to monitor uploads is leveraging SharePoint's default list view settings.

Access Column Settings

Navigate to your SharePoint document library. Click on the 'Add a column' option at the end of the column headers.

Open View Settings

Scroll down in the dropdown menu and select 'Show or hide columns' to open the advanced view settings pane on the right side of the screen.

Enable Required Columns

Check the boxes for the default 'Name (linked to document with edit menu)' column to view extensions, and the 'File size' column to track the size of uploaded documents.

Apply Changes

Click the 'Apply' button to save the view. You can now easily review the extensions and sizes of all uploaded files in the library.

Manual Monitoring: This method does not block uploads automatically but allows administrators to filter, sort, and visually audit files that do not meet internal size or extension policies.

Solution 2

Implement Custom Validation with Power Apps or SPFx

If you require strict, automated rules to block unsupported file types or large files, you must build a custom solution using modern SharePoint development frameworks.

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Frequently Asked Questions

Why can't I use Remote Event Receivers for file validation in SharePoint Online?

Microsoft has officially retired the Remote Event Receiver add-in for SharePoint Online. This means it is no longer a supported option for out-of-the-box form validation, and you must adopt modern development practices like Power Apps or SharePoint Framework (SPFx).

Can I automatically block users from uploading files larger than a specific size in a document library?

Without custom development, SharePoint Online does not natively allow you to set custom maximum file size rules on a per-library basis. You must either use Power Apps to enforce logic on custom forms or rely on the default 'File size' column to audit uploads manually.

How do I make file extensions visible for all documents in a SharePoint library?

You can display file extensions by modifying the library view. Click 'Add a column', select 'Show or hide columns', and enable the default 'Name (linked to document with edit menu)' column, which renders the exact file name including its extension.

Document & File Issues