SourceTree - external diff tool doesn't launch and conflicts disappear


I am using SourceTree with Xcode's FileMerge. This has always worked fine. Today, when I right click->resolve using external diff tool, I get a window for a second showing that the launch is happening, and then nothing and the conflict disappears as though resolved. This is really bad as I am unable to merge changes.

Going into preferences, I tried to change the diff tool, but I can't click on any of the values - everything seems to be locked.


12 answers

I had the same problem, it turns out it was an Xcode problem

Run: sudo xcode-select -s /Applications/


This worked for me

This worked for me

Yes that worked for me, using FileMerge

I have no idea what this command is doing, but it fixed my problem. Thank you.

Super! this works for me.

Worked for me running SourceTree 2.7.6 (177) and Xcode 9.4.1.

Thanks, solved by run that magic command.

  • When the diff tool is not (correctly) configured, it behaves the way you described. (not very informative...)
  • In Tools\Options\General, you need to enable "Allow SourceTree to modify your global config files" at the top before you can change the Diff settings.
  • If you have the Diff / Merge tools set to "System default" (this is the default setting), it seems to never work.

So I think what you need to do is:

  1. enable the "Allow..." option
  2. change the diff tool to explicitly specify the right tool with the right cmd options

This is still not working for me. THe external diff tool does not launch!

Thanks. It work perfect

In Mac, I had to go to SourceTree/Preferences/General


This did not work for me. That option is checked, Diff/Merge tool is set explicitly to FileMerge (which is what it was using before it abruptly stopped working), and as recommended in another answer here, I have it set to Embedded Git rather than System Git, but none of that helped at all.

It used to work fine, and then suddenly stopped working a while back, without my having changed any configuration options whatsoever. I'm guessing it was when SourceTree automatically updated itself or something... But anyway, none of the answers in this post have helped for me.

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Tested with Sourcetree v2.7.1 and DiffMerge v4.2.1 (with command line tools) on MacOS v10.13.3:

1. Open Sourcetree prefs and select `Diff` tab

2. Set `Visual Diff Tool` menu to `Custom`

3. Set `Diff command` field to: /usr/local/bin/diffmerge

4. Set `Arguments` field to: $LOCAL $REMOTE

5. Close prefs, select External Diff (or cmd-D) and observe DiffMerg launches.


More info here:

You can do the same for "Merge Command" too.

Merge Command:



--merge --result="$MERGED" "$LOCAL" "$BASE" "$REMOTE"
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I found changing to the Embedded Git rather than System Git fixed the problem.

this resolved my issue as well

this resolved my issue as well. I had tried with DiffMerge & Beyond Compare. Switching to System Git fixed it for me

This resolved my Issue.

None of these worked for me either. Using latest SourceTree with Beyond compare. It doesn't happen on every file. I don't know what the common factor is on the files that it does happen with. 



So it turns out the two files I was just trying to merge, the difference was that the file was no longer existent on the remote server. Rather than do something about the merge to show it was deleted, it just hung forever.

This was the right answer. Files no longer exist on remote server. 

Same problem here. I had to accept the user agreement in the terminal before it would launch from SourceTree. Running 'sudo opendiff' worked for me.

 This was it for me

Hi Yair,

I had the same problem.

As Balazs said, it was because the "System default" was selected for the merge tool. Download a tool and set it as your resolving tool.

If none of these things work, try running `opendiff` in the Terminal. 

It there's an error like below you need to do one of two things: 

  • Install XCode
  • Install another diff program

As of writing SourceTree supports the following programs:

  • Araxis Merge
  • Beyond Compare
  • BBEdit
  • DiffFork
  • DiffMerge
  • Changes
  • FileMerge
  • Kaleidoscope
  • KDiff3
  • P4Merge
  • TextWrangler



I had same problem.

  1. open your git global config file.
  2. check syntax error.

then I can fix the problem.

I think this is sourcetree bug.

Yup, the path to diffmerge had part of it duplicated. Fixing it did the trick. Thanks!

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The fix is yet to arrove but there's a workaround at

As a workaround I changed the name of my external diff app from




Thus my diff command becomes


with arguments


Even when I edited the .gitconfig diff tool path and fixed it by removing portion of the path, each time I'd restart DiffMerge, it would reappear.


So, here's the workaround.

1. Symlink DiffMerge to another location (so it's not auto-detected as DiffMerge)

ln -s /Application/ /Applications/

2. Then select a custom diff and merge tool arguments.

Diff command arguments:

--nosplash "$LOCAL" "$REMOTE"

Merge tool arguments:

--merge --result="$MERGED" "$LOCAL" "$BASE" "$REMOTE"

Screen Shot 2018-11-07 at 7.03.22 PM.png

After this, SourceTree will no longer mangle the path at startup because it doesn't think it's DiffMerge anymore.

Nothing above works anymore for diffmerge. Is there going to be a fix in next release or shall we just try any and every solution?

I just posted a reply above that works as off SourceTree v3.0

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