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KB: Control Which Altium Designer Version Opens from Altium 365 Web

Created: April 24, 2026 | Updated: April 24, 2026
A365 A365
When opening a project from the Altium 365 Web interface, Windows controls which installed Altium Designer version is launched, which can result in an unexpected version opening on systems with multiple Altium Designer installations. The Altium 365 Web UI uses a Windows protocol handler (DXP) to start the desktop application, and the specific executable that is launched is defined by a registry association rather than by browser settings or Altium 365 preferences. By updating the registry entry for the DXP protocol to reference a specific X2.exe executable, users can control which Altium Designer version opens when launching projects directly from Altium 365 Web. This procedure applies to Windows systems only.

Solution Details

Unexpected Altium Designer version opens

When selecting Open Project in Altium Designer in the Altium 365 Web UI, the project may open in an unintended version of Altium Designer. This issue is most commonly observed on Window systems where multiple versions of Altium Designer are installed in parallel.

Altium 365 web interface showing a schematic view open in the browser, with project navigation on the left, SCH view selected, and an Open Project in Altium Designer button to launch the same project in the desktop application.
Opening the Project in Altium Designer from the Altium A365 Web UI
Windows File Explorer showing the Program Files\Altium directory with multiple installed Altium Designer versions listed as folders.
Example with multiple parallel installations of different versions of Altium Designer

DXP protocol controls launched executable

The Altium 365 Web UI uses a custom Windows URL/protocol handler named DXP to open projects in the local desktop application. Windows resolves this handler through a registry association that specifies the exact X2.exe executable to run. As a result, the version of Altium Designer that launches is controlled entirely by this registry entry, not by browser settings or Altium 365 preferences.

Redirect the protocol to the intended version

The resolution is to update the Windows registry entry for the DXP protocol so that it points to the X2.exe executable of the desired Altium Designer version. 

Modify the registry command for DXP handler

  1. Open the Windows Registry Editor (administrator privileges are required).
  2. Navigate to:
    Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Classes\DXP\shell\open\command
  3. Locate and edit the (Default) value.
  4. Set the value data to the full path of the intended X2.exe executable, followed by "%1".
  5. Click OK to save the change.
  6. Return to the Altium 365 Web UI and click Open Project in Altium Designer to verify that the correct version launches.

Use the following syntax:

Name: (Default)
Type: REG_SZ
Data: "<Path to desired version of X2.exe>" "%1"

Example:

"C:\Program Files\Altium\AD26.5.0\X2.exe" "%1"
Windows Registry Editor showing the key HKEY_LOCAL_MACHINE\SOFTWARE\Classes\DXP\shell\open\command, with the Default value pointing to an Altium Designer executable path, indicating which installed version launches DXP files.
Editing the Registry to specify which version of Altium Designer should be launched from A365 Web UI

Additional Notes

  • Editing registry keys under HKEY_LOCAL_MACHINE requires administrator access.
  • Before making any changes, it is recommended to back up the Windows registry to allow recovery if an incorrect modification prevents Altium Designer from launching correctly.

References

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