1. For 3-way merging, you need to click on the External Merge Tool option instead, which will only be available if there are any unsolved conflicts. If you are not restricted to Sourcetree + Meld, I reckon the Git Extensions + KDiff3 suite could be a good open-sourced alternative also.
2. Diff Command: C: Program Files (x86) Meld Meld.exe. When I right-click on a conflicted file and select 'Resolve Conflicts' 'Open External Merge Tool' I get the dialog for 'Visual Merge in Process' but the merge tool does not open. The path is correct. I am using Sourcetree for Windows, v2.6.10.0.

1. Sourcetree Launch External Merge Tool Disabled
2. Launch External Merge Tool Sourcetree
3. Launch External Merge Tool Sourcetree Mac

To resolve a conflict, right click on a conflicted file in SourceTree, Resolve Conflicts Launch External Merge Tool, resolve conflicts in Visual Studio and finish by clicking Accept Merge. That’s all there is to it. Now if you, like me, like Visual Studio’s merge tool then you’re literally 5 minutes away from linking it to SourceTree.

Sourcetree Launch External Merge Tool Disabled

Edit onlineThe file comparison tool can be integrated with Sourcetree so that you can use it to compare changes. The advantages of doing this include:

• The OxygenCompare Files tool presents the files side-by-side and makes it much easier to determine real changes.
• The OxygenCompare Files tool includes XML comparison algorithms.
• The OxygenCompare Files tool includes various options for configuring the comparison.
• The OxygenCompare Files tool allows you to navigate through changes.

To integrate the Compare Files tool with Sourcetree, follow this procedure, depending on your operating system:

Windows

1. In Sourcetree, go to Tools > Options.
2. Go to the Diff tab.
3. In the External Diff/Merge section, configure the settings as follows:
   • External Diff Tool - Select Custom.
   • Diff Command - Enter the path of the OxygendiffFile.exe file (for example: c:ProgramsOxygen XML Editor 19diffFiles.exe).
   • Arguments - Enter -ext $REMOTE $LOCAL $LOCAL.
   • Merge Tool - Select Custom.
   • Diff Command - Enter the path of the OxygendiffFile.exe file (for example: c:ProgramsOxygen XML Editor 19diffFiles.exe).
   • Arguments - Enter -ext $LOCAL $REMOTE $BASE $MERGED.
4. Click OK.

Launch External Merge Tool Sourcetree

Result: In Sourcetree, you can now compare file changes with the OxygenCompare Files tool by simply selecting External Diff from the contextual menu, Actions menu, or Ctrl+D.

macOS

Launch External Merge Tool Sourcetree Mac

1. In Sourcetree, go to Sourcetree > Preferences.
2. Go to the Diff tab.
3. In the External Diff/Merge section, configure the settings as follows:
   • External Diff Tool - Select Custom.
   • Diff Command - Enter a command-line argument to launch the OxygendiffFiles.sh file (for example: sh '/Applications/Oxygen XML Editor/diffFiles.sh').
   • Arguments - Enter -ext $REMOTE $LOCAL $LOCAL.
   • Merge Tool - Select Custom.
   • Diff Command - Enter a command-line argument to launch the OxygendiffFiles.sh file (for example: sh '/Applications/Oxygen XML Editor/diffFiles.sh').
   • Arguments - Enter -ext $LOCAL $REMOTE $BASE $MERGED.
4. Close the preferences dialog box.

Result: In Sourcetree, you can now compare file changes with the OxygenCompare Files tool by simply selecting External Diff from the contextual menu or Actions menu.