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Cannot Launch KDiff3 External Merge Tool from Sourcetree

Matt Erman Nov 01, 2017

I am not sure what the issue is all of a sudden.  It was working a few times, then all of a sudden it no longer will work.  It says it is launching the tool but then nothing happens.  I am unable to effectively resolve conflicts and need this to work properly.  


I updated to 2.3.5 and it still isn't working.  Has anyone else solved this issue?

6 answers

1 accepted

0 votes
Answer accepted
Matt Erman Nov 05, 2017 • edited

To anyone else having this problem do yourself a favor and download GitKraken.  Problem solved.  They apparently know how to use GitMerge and GitDiff properly.

Lee Harrington Dec 03, 2018

This is not a real solution to the issue at hand. It is just using a different product.

Like Brian Boyd likes this
2 votes
Michael Minns Atlassian Team Nov 08, 2017

I use KDiff3 daily and its working for me. Can you provide some more details so we can try and work out the differences?

Can you check the git config settings, does it contain:

mergetool.sourcetree.cmd='C:/Program Files/KDiff3/kdiff3.exe' "$BASE" "$LOCAL" "$REMOTE" -o "$MERGED"

Sourcetree uses that setting by running

 git mergetool -y --tool=Sourcetree {filename}

Does that work from your command line?

Michael Minns Atlassian Team Nov 08, 2017

you can try the diff equivalent as well 


git difftool -y tool=Sourcetree {oldcommithash} -- {filename}

Like ilia lobov likes this
1 vote
Matt Erman Nov 05, 2017 • edited

This is straight up Bullcrap from a "professional" software developer to release something with such a buggy MUST HAVE feature.  How the hell can you release a product that for half the people there is no way to open an external merge/diff tool because sourcetree screws something up that leaves you attempting to go through 50 different posts to try and fix, STILL unsuccessfully I might add...


This is completely unacceptable.  I'm sorry but until Atlassian gets their head out of their ass and fixes this bug that has been in countless versions, including the latest one, I'm done using it.    I've spent 5 hours trying to resolve it, I don't have anymore time to play "find a workaround for my broken features".

1 vote
Piotr Gradkowski Jun 28, 2018

In my case there's a tweak to this issue: I have a merge with a number of conflicts to resolve. I can resolve 1 conflict using kdiff3 (the KDiff3 commands configured as suggested by Joshua Brown). After this one conflict is resolved, I can't resolve any other - KDiff3 doesn't launch, as described above.

Michael Minns Atlassian Team Jul 03, 2018


KDiff will not  trigger if, for example, the file in conflict has been deleted in one side of the merge or I've also seen cases where Sourcetree/Git appears to report a file in conflict but without any changes, possibly just whitespace? In this case KDiff will not trigger either.

We are aware of some of these annoying edge cases and plan to improve them in the future.

Todd Menier Oct 09, 2018

@Michael Minns A file being deleted on one side of the merge is considered an edge case? Took me forever to figure out that this is why KDiff didn't open. But now that I know I'll be on the lookout for it. Thanks.

0 votes
Joshua Brown Nov 09, 2017

Yesterday it wasn't working for me. Today, it magically is. Here are the contents of my .gitconfig file.


[difftool "sourcetree"]
cmd = 'C:/kdiff3/kdiff3.exe' \"$LOCAL\" \"$REMOTE\"
[mergetool "sourcetree"]
cmd = 'C:/kdiff3/kdiff3.exe' \"$BASE\" \"$LOCAL\" \"$REMOTE\" -o \"$MERGED\"

Dwayne Perkins Nov 14, 2018

Your answer helped me because the mergetool setting wasn't in my .gitconfig file.  Putting it in there manually did not help, but it did make me take a 2nd look at the settings in the sourcetree UI.   I did not have the mergetool configured correctly.

Victor Cheung Nov 14, 2018

This helped me too as I am a windows sourcetree user.  

Another problem I had was in the sourcetree options.  Under the "Diff" tab options there are 2 settings, one for "External Diff Tool" and one for "Merge Tool".  I assumed I had to set the "External Diff Tool" because it had the word "External" in it, but it was actually the "Merge Tool" that I had to set in order for it to work.  This should be called "External Merge Tool".  -_-

0 votes
Dwayne Perkins Nov 14, 2018

I was having the same problem.  There are two settings in sourcetree in the Tools->options menu under the Diff tab where you need to set it to Kdiff3: the diff tool and the merge tool.  Ensure that both of them are configured to used Kdiff3.   I failed to notice that my merge tool settings were set to "System Default".   As soon as I fixed this, everything worked normally.

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