# Diff tool support

> Understand the diff tools that Unity supports, and how to set up a custom revision tool.

You can use the [**Revision Control Diff/Merge** setting](/engine/6000.7/manual/unity-editor/editor-settings-reference/preferences/external-tools.md) to set an installed diff tool as the default revision tool. You can also use this setting to define a custom revision tool with specific layouts.

If you want to change the diff tool that Unity uses, open the [Preferences](/engine/6000.7/manual/unity-editor/editor-settings-reference/preferences.md) window, and navigate to the **External Tools** section. Select your preferred tool from the **Revision Control Diff/Merge** dropdown list.

## Set up a custom revision tool

To set up a custom revision tool, follow these steps:

1. Open the [Preferences](/engine/6000.7/manual/unity-editor/editor-settings-reference/preferences.md) window, and navigate to the **External Tools** section.
2. In the **Revision Control Diff/Merge** dropdown list, select **Custom Tool**.
3. Enter the path to the custom tool's installation folder. On macOS, this should point to the *Contents / MacOS* folder in the tool's installation folder.
4. Enter the arguments for two-way diffs, three-way diffs, and merges.

To specify file layout in the revision tool, use these arguments:

| **Property**   | **Function**                       |
| -------------- | ---------------------------------- |
| `#LTITLE`      | Left title                         |
| `#RTITLE`      | Right title                        |
| `#ATITLE`      | Ancestor title                     |
| `#LEFT`        | Left file                          |
| `#RIGHT`       | Right file                         |
| `#ANCESTOR`    | Ancestor file                      |
| `#OUTPUT`      | Output file                        |
| `#ABSLEFT`     | Absolute path to the left file     |
| `#ABSRIGHT`    | Absolute path to the right file    |
| `#ABSANCESTOR` | Absolute path to the ancestor file |
| `#ABSOUTPUT`   | Absolute path to the output file   |

Examples:


**SourceGear DiffMerge:**
![](/api/media?file=/engine/6000.7/media/images/SourceGearDiffMerge.png)


**P4Merge:**
![](/api/media?file=/engine/6000.7/media/images/P4DiffMerge.png)

## Additional resources

* [Preferences reference](/engine/6000.7/manual/unity-editor/editor-settings-reference/preferences.md)
* [Version control integrations](/engine/6000.7/manual/get-started/project-configuration/version-control/versioncontrolintegration.md)