Version: 2022.3
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Smart merge

Use the UnityYAMLMerge tool to merge sceneA Scene contains the environments and menus of your game. Think of each unique Scene file as a unique level. In each Scene, you place your environments, obstacles, and decorations, essentially designing and building your game in pieces. More info
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and prefabAn asset type that allows you to store a GameObject complete with components and properties. The prefab acts as a template from which you can create new object instances in the scene. More info
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files in a semantically correct way. The tool can be accessed from the command line and is also available to third-party version controlA system for managing file changes. You can use Unity in conjunction with most common version control tools, including Perforce, Git, Mercurial and PlasticSCM. More info
See in Glossary

Setting up smart merging in Unity

In the Version Control project settings (menu: Edit > Project Settings > Version Control), when you select a third-party version control tool in the Mode field, for example Perforce or PlasticSCM, the Smart Merge is displayed. The menu has the following options:

  • Off: use only the default merge tool set in the preferences with no smart merging.
  • Premerge: enable smart merging, accept clean merges. Unclean merges will create premerged versions of base, theirs and mine versions of the file. Then, use these with the default merge tool.
  • Ask: enable smart merging but when a conflict occurs, show a dialog to let the user resolve it (this is the default setting).

Setting up UnityYAMLMerge for use with third-party tools

The UnityYAMLMerge tool is shipped with the Unity editor; assuming Unity is installed in the standard location, the path to UnityYAMLMerge will be:

C:\Program Files\Unity\Editor\Data\Tools\UnityYAMLMerge.exe


C:\Program Files (x86)\Unity\Editor\Data\Tools\UnityYAMLMerge.exe

…on Windows and


…on Mac OSX (use the Show Package Contents command from the Finder to access this folder).

UnityYAMLMerge is shipped with a default fallback file (called mergespecfile.txt, also in the Tools folder) that specifies how it should proceed with unresolved conflicts or unknown files. This also allows you to use it as the main merge tool for version control systems (such as git) that don’t automatically select merge tools based on file extensions. The most common tools are already listed by default in mergespecfile.txt but you can edit this file to add new tools or change options.

You can run UnityYAMLMerge as a standalone tool from the command line (you can see full usage instructions by running it without any arguments). Setup instructions for common version control systems are given below.


  1. Go to Preferences > Merge.
  2. Select Other application.
  3. Click the Add button.
  4. In the extension field, type .unity.
  5. In the Application field, type the path to the UnityYAMLMerge tool (see above).
  6. In the Arguments field, type merge -p %b %1 %2 %r
  7. Click Save.

Then, follow the same procedure to add the .prefab extension.


Add the following text to your .git or .gitconfig file:

    tool = unityyamlmerge

    [mergetool "unityyamlmerge"]
    trustExitCode = false
    cmd = '<path to UnityYAMLMerge>' merge -p "$BASE" "$REMOTE" "$LOCAL" "$MERGED"


Add the following text to your .hgrc file:

    **.unity = unityyamlmerge
    **.prefab = unityyamlmerge

    unityyamlmerge.executable = <path to UnityYAMLMerge>
    unityyamlmerge.args = merge -p --force $base $other $local $output
    unityyamlmerge.checkprompt = True
    unityyamlmerge.premerge = False
    unityyamlmerge.binary = False


Add the following to your ~/.subversion/config file:

    merge-tool-cmd = <path to UnityYAMLMerge>


  1. Go to Preferences > Diff Viewer > Merge Tool and click the Advanced button.
  2. In the popup, type .unity in the extension field.
  3. In the External Program field type:
    <path to UnityYAMLMerge> merge -p %base %theirs %mine %merged

Then, follow the same procedure to add the .prefab extension.


  1. Go to Preferences > Merge Tools and click the Add button.
  2. Select External merge tool.
  3. Select Use with files that match the following pattern.
  4. Add the .unity extension.
  5. Enter the command:
    <path to UnityYAMLMerge> merge -p "@basefile" "@sourcefile"  "@destinationfile" "@output"

Then, follow the same procedure to add the .prefab extension.


  1. Go to Tools > Options > Diff.
  2. Select Custom in the Merge Tool dropdown.
  3. Type the path to UnityYAMLMerge in the Merge Command field.
  4. Type merge -p $BASE $REMOTE $LOCAL $MERGED in the Arguments field.

Configuring mergerules.txt

To customize how UnityYAMLMerge merges files, configure the mergerules.txt file. This is available in the Editor/Data/Tools folder of your Unity installation. The various configuration options are as follows.


The arrays configuration section tells UnityYAMLMerge to treat the specified path as an array; either as a “set” with a key value, or as a “plain” array without key values. The default for all arrays is to do a hybrid mode and try to match with some known heuristics.

  • <mode> is one of “set” or “plain”

Example (as per default mergerules file)

set *.GameObject.m_Component *.fileID
set *.Prefab.m_Modification.m_Modifications target.fileID target.guid propertyPath
plain *.MeshRenderer.m_Materials
plain *.Renderer.m_Materials


The exclusions configuration section indicates which paths to exclude from merging. If both sides have been modified, they are then treated as a conflict and will show up for user input.

  • <mode> is one of “include”, “exclude”, “includeIfContains”, “excludeIfContains”

Example (as per default mergerules file)

exclude *.MeshRenderer.m_Materials.*
exclude *.SpriteRenderer.m_Materials
exclude *.SpriteRenderer.m_Color
include *.ParticleSystem.InitialModule
exclude *.ParticleSystem.*
exclude *.ParticleSystem.InitialModule.*
#excludeDepend *.MonoBehaviour m_Script ^m_
excludeIfContains *.MonoBehaviour.* x y z
excludeIfContains *.MonoBehaviour.* r g b


The comparisons section takes into account negligible differences between float values to ignore per user settings. When enabled, floating point comparison is done relatively to account for relative error. You can configure comparison in the following ways:

  • “float” <float value to compare> (This sets epsilon to a default value close to machine epsilon)
  • “float” <float value to compare> <relative comparison value and absolute cutoff>
  • “float” <float value to compare> <relative comparison value> <absolute comparison cutoff>

The relative comparison value determines epsilon and how comparison will scale with the size of the floats’ relative error. The absolute comparison cutoff determines at which point float comparison switches from absolute to relative from zero (on a graph).

Note: Comparison values should be between float epsilon (~0.00000011921) and 1.0


float *.Transform.m_LocalPosition.x 0.0000005
float *.Transform.m_LocalPosition.y 0.0000005
float *.Transform.m_LocalPosition.z 0.0000005
float *.Transform.m_LocalRotation.x 0.00005 0.001
float *.Transform.m_LocalRotation.y
float *.Transform.m_LocalRotation.z 0.00005 0.001
float *.Transform.m_LocalRotation.w
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