Configure UDFs in Excel Online in Office Online Server

Use user-defined functions (UDFs) in Excel Online in Office Online Server to call custom functions.

User-defined functions (UDFs) in Excel Online enable you to call custom functions written in managed code by using formulas in cells. You can use UDFs to:

  • Call custom mathematical functions.

  • Get data from custom data sources into worksheets.

  • Call web services.

You can install UDF binaries in one of two locations:

  • A local directory. For example:


  • The global assembly cache. For example:

    CompanyName.Hierarchichal.MyUdfNamespace.MyUdfClassName.dll, Version=, Culture=en, PublicKeyToken=e8123117d7ba9ae38

Reference the location when you create a New-OfficeWebAppsExcelUserDefinedFunction definition on the Office Online Server.


Office Online Server does not support UDFs located on network shares.

Enable UDFs on Office Online Server

When an adminstrator creates a new Office Web Apps Server farm by using the New-OfficeWebAppsFarm Windows PowerShell cmdlet, UDF assemblies are disabled by default. The default value of the ExcelUdfsAllowed flag is false.

To enable UDFs, run the following Windows PowerShell command on the Office Online Server, after the Office Web Apps Server farm has been created.

Set-OfficeWebAppsFarm - ExcelUdfsAllowed:$true

Create UDF definitions on Office Online Server

After you enable UDFs, you need to create a definition for the binary that contains the UDFs. To create a definition for your UDF binary on the Office Online Server, use the New-OfficeWebAppsExcelUserDefinedFunction cmdlet. This cmdlet includes the following parameters:

  • Assembly

  • AssemblyLocation

  • Enable (set to False by default)

  • Description

The following examples show how create the UDF definitions.

New-OfficeWebAppsExcelUserDefinedFunction -Assembly c:\myudf.dll -AssemblyLocation LocalFile -Enable:$true -Description "My Server UDFs"

New-OfficeWebAppsExcelUserDefinedFunction -Assembly "CompanyName.Hierarchichal.MyUdfNamespace.MyUdfClassName.dll, Version=, Culture=en, PublicKeyToken=e8123117d7ba9ae38" -AssemblyLocation GAC -Enable:$true -Description "My GAC Server UDFs"

After you create the new UDF reference, run iisreset on the server to pick up the reference immediately.

Additional Office Online Server UDF Windows PowerShell commands

Use the following Windows PowerShell cmdlets to work with UDFs:

  • Get-OfficeWebAppsExcelUserDefinedFunction (no required parameters) - Returns a list of UDF definitions that are configured on the Office Online Server.

  • Set- OfficeWebAppsExcelUserDefinedFunction (Identity parameter required) - Sets properties on existing UDF definitions.

  • Remove-OfficeWebAppsExcelUserDefinedFunction (Identity parameter required) - Removes existing UDF definitions.

UDF sample

The following files provide a sample workbook that uses a UDF and the UDF binary:

See also