SharePoint Document Issues

Why SharePoint Adds an Underscore to Folder Names & How to Fix It

Chanuka Geekiyanage Oct 16, 2026 869 views

Question details

The user needs to understand why an underscore is being appended to their folder or file names in SharePoint and how to resolve it.

Why SharePoint Adds an Underscore to Folder Names

Product: SharePoint
Device & OS: not provided
Scenario: Creating, uploading, or renaming files and folders within a SharePoint document library or synchronized OneDrive folder.
Observed behavior: SharePoint automatically adds an underscore to the end of a file or folder name if it violates system naming conventions or ends with a restricted string.

Before you start

Verify that you have Edit permissions for the SharePoint document library and temporarily pause OneDrive syncing if you plan to batch-rename multiple affected folders.

Solution 1Recommended

Rename the Folder to Comply with SharePoint Naming Rules

Identify the restricted characters or naming patterns causing the underscore and rename the folder with an acceptable alternative.

SharePoint and OneDrive have strict naming policies to prevent synchronization issues across different operating systems. When you attempt to save a folder using a restricted name (like system-reserved names 'CON' or 'PRN'), or if the name ends with a forbidden string (such as a period, a trailing space, or '_files'), SharePoint automatically intercepts the action. Instead of rejecting the upload entirely, it modifies the name by adding an underscore to make it valid. This behavior cannot be disabled.

Locate the affected folder

Navigate to the SharePoint document library where the folder with the unwanted underscore is currently stored.

Initiate the rename action

Hover over the folder, click the 'Show actions' icon (three dots/ellipsis) next to the folder name, and select 'Rename' from the dropdown menu.

Enter a compliant name

Type a new name ensuring it does not contain restricted characters (e.g., ~, ", #, %, &, *, :, <, >, ?, /, \, {|}) and does not end with a space or a period.

Save the new name

Click 'Save' or press the Enter key. Check the folder to confirm the underscore is no longer being appended.

Rename the Folder to Comply with SharePoint Naming Rules

System Reserved Names: Ensure you are not using names reserved by the Windows operating system, such as AUX, PRN, NUL, CON, COM1-COM9, LPT1-LPT9, or names beginning with `~$`.

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Frequently Asked Questions

What specific characters trigger the automatic underscore in SharePoint?

SharePoint will modify or reject folder names containing characters such as tildes (~), number signs (#), percents (%), ampersands (&), asterisks (*), braces ({ }), backslashes (\), colons (:), angle brackets (< >), question marks (?), slashes (/), pluses (+), pipes (|), and quotation marks (").

Why did SharePoint add an underscore when I didn't use any special characters?

Even if you avoid special characters, SharePoint will append an underscore if your folder name ends with a space or a period, or if you use system-reserved names like 'CON', 'PRN', or 'NUL'.

Is it possible to disable this automatic renaming feature in SharePoint?

No, this is a built-in safety mechanism designed to prevent the creation of invalid file paths that could cause severe synchronization and access errors. You must comply with the naming restrictions to avoid the underscore.

Does this naming restriction apply to both SharePoint and OneDrive?

Yes, because OneDrive for Business is built on SharePoint infrastructure, both platforms share the exact same file and folder naming restrictions and behaviors.

Document & File Issues