feat(extensions): add support for custom themes in extensions by spencer426 · Pull Request #17327 · google-gemini/gemini-cli

spencer426 · 2026-01-22T18:45:18Z

Summary

This PR introduces support for extensions to contribute custom themes to Gemini CLI. With this change, extensions can include a themes property
in their gemini-extension.json file. These themes will be automatically discovered, loaded, and made available for users to select from in the
theme dialog.

Details

To enable this functionality, the ExtensionManager has been updated to handle the registration and unregistration of themes as extensions are
activated or deactivated. The ThemeManager was refactored to manage themes from multiple origins—user settings, extensions, and direct file
paths—while ensuring proper namespacing to prevent any naming conflicts.

As a result, the ThemeDialog has been streamlined to source its list of themes directly from the ThemeManager. Additionally, the CustomTheme
interface has been relocated to @google/gemini-cli-core, making it accessible to extension developers.

Related Issues

Fixes #16192

How to Validate

Create a new extension and, in its gemini-extension.json file, add a themes property with at least one custom theme. For example:

{
  "name": "my-custom-theme-extension",
  "version": "0.0.1",
  "themes": [
    {
      "name": "My-Awesome-Theme",
      "type": "custom",
      "text": {
        "primary": "#FF00FF"
      }
    }
  ]
}

Install the extension in Gemini CLI using gemini extensions link PATH_TO_EXTENSION.
Launch gemini and open the theme selection dialog using /theme.
Confirm that the new theme (e.g., my-theme-extension: My-Awesome-Theme) is listed.
Select the theme and verify that its styles are correctly applied.
Uninstall the extension.
Re-open the theme selection dialog and ensure the theme has been removed from the list.

Pre-Merge Checklist

gemini-code-assist · 2026-01-22T18:45:38Z

Summary of Changes

Hello @spencer426, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a significant enhancement to the Gemini CLI by enabling extensions to provide their own custom themes. This allows for greater personalization and integration within the CLI ecosystem. The core changes involve updating the extension and theme management systems to seamlessly handle these new theme contributions, ensuring they are correctly loaded, displayed, and managed without conflicts, ultimately enriching the user experience with more diverse visual options.

Highlights

Extension Theme Support: Extensions can now contribute custom themes to the Gemini CLI by including a 'themes' property in their 'gemini-extension.json' file.
Automated Theme Management: The ExtensionManager automatically discovers, registers, and unregisters these themes as extensions are activated or deactivated.
Refactored ThemeManager: The ThemeManager has been updated to manage themes from various origins (user settings, extensions, file paths) with proper namespacing to prevent conflicts.
Streamlined ThemeDialog: The ThemeDialog now directly sources all available themes from the ThemeManager, simplifying its logic and consolidating theme display.
CustomTheme Interface Relocation: The 'CustomTheme' interface has been moved to '@google/gemini-cli-core', making it readily accessible for extension developers.

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Code Review

The pull request introduces support for custom themes in extensions, allowing extensions to contribute themes that are automatically discovered and managed by the CLI. The ExtensionManager and ThemeManager have been updated to handle the registration and unregistration of these themes, including proper namespacing to prevent conflicts. The ThemeDialog has been streamlined to source themes directly from the ThemeManager, and the CustomTheme interface has been moved to @google/gemini-cli-core for broader accessibility. Tests have been added to cover the new theme loading functionality.

Overall, the changes are well-structured and implement the new feature effectively. However, there are a couple of areas that could be improved for better adherence to best practices and test maintainability, specifically regarding the use of synchronous file system operations in tests and proper cleanup of environment variables to ensure test isolation.

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+const tempHomeDir = fs.mkdtempSync(
+  path.join(fs.realpathSync('/tmp'), 'gemini-cli-test-'),


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+const tempHomeDir = fs.mkdtempSync(
+  path.join(fs.realpathSync('/tmp'), 'gemini-cli-test-'),
+);
+process.env['GEMINI_CLI_HOME'] = tempHomeDir;


github-actions · 2026-01-22T19:29:16Z

Size Change: +3.55 kB (+0.02%)

Total Size: 23.5 MB

Filename	Size	Change
`./bundle/gemini.js`	23.5 MB	+3.55 kB (+0.02%)

ℹ️ View Unchanged

Filename	Size
`./bundle/sandbox-macos-permissive-closed.sb`	1.03 kB
`./bundle/sandbox-macos-permissive-open.sb`	890 B
`./bundle/sandbox-macos-permissive-proxied.sb`	1.31 kB
`./bundle/sandbox-macos-restrictive-closed.sb`	3.29 kB
`./bundle/sandbox-macos-restrictive-open.sb`	3.36 kB
`./bundle/sandbox-macos-restrictive-proxied.sb`	3.56 kB

_{compressed-size-action}

This change introduces the ability for extensions to define and register custom themes. Extensions can now include a property in their file, and these themes will be loaded and made available to the user. Fixes #16192

jacob314 · 2026-01-22T20:32:53Z

-    return a.label.localeCompare(b.label);
-  });
+    })
+    .sort((a, b) => {


why did this change?

We are now merging built-in themes with extension-provided themes, the list is no longer guaranteed to be in order. This sort ensures alphabetical list regardless of the source.

jacob314 · 2026-01-22T20:34:07Z

+      return;
+    }
+
+    debugLogger.log(


log this as debug or do not log. this is a bit spammy to log for all users.

Done, deleted.

jacob314 · 2026-01-22T20:37:28Z

-        this.activeTheme,
-      );
+      const isCustom =
+        [...this.settingsThemes.values()].includes(this.activeTheme) ||


there are a bunch of dupe checks searching all 3 lists. please simplify by adding a helper that returns a list of all custom themes.

Done, created a private _getAllCustomThemes() helper to consolidate custom themes.

jacob314 · 2026-01-22T20:39:05Z

  overrides?: Record<string, AgentOverride>;
 }

+export interface CustomTheme {


Is this now duplicated in package/cli and package/core? Please simplify so we only have one class defining a theme.
is there a reason this has to be in packages/core not packages/cli?

Done, removed the duplicate CustomTheme interface from packages/cli/src/ui/themes/theme.ts, redirecting all imports within packages/cli to @google/gemini-cli-core.

Thanks for addressing this! Moving the CustomTheme interface to @google/gemini-cli-core and updating the imports in packages/cli is a great way to centralize the definition and avoid duplication. This improves maintainability and ensures a single source of truth for theme definitions across the project.

jacob314 · 2026-01-22T20:39:58Z

+    }
+  }
+
+  protected override async stopExtension(extension: GeminiCLIExtension) {


please add a test verifying that stopping an extension with a theme causes the theme to change back to the default theme if that custom theme was in use.

Added a "Should revert to default theme when extension is stopped" spec in packages/cli/src/config/extension-manager-themes.spec.ts

jacob314

Done with a round of review comments. Overall looks promising!

jw408 · 2026-01-23T06:30:45Z

@spencer426 CI is failing due to an unused import. I think the fix is to remove
GEMINI_MODEL_ALIAS_AUTO from line 16 of packages/cli/src/config/settingsSchema.ts

The test in was failing because the provided to was missing the method. This commit adds the missing with a mocked method to the to correctly reflect the interface expected by .

spencer426 · 2026-01-23T16:50:40Z

@jw408 Thanks the issue with GEMINI_MODEL_ALIAS_AUTO has been resolved!

jacob314 · 2026-01-23T22:21:06Z

+  "version": "1.0.0",
+  "themes": [
+    {
+      "name": "My-Awesome-Theme",


Can you make this theme reasonable. For example, do a shades of green theme where everything is green. Will be clearer than this one where all that changes is the primary color is different which is odd but not really recognizable.

Makes sense, I updated the example.

jacob314 · 2026-01-23T22:22:41Z

+    ```
+
+    Alternatively, you can set it through the UI by running `gemini` and then
+    pressing `t`.


this is not correct. pressing t does not change the theme. Please update to the correct shortcut.

jacob314

Restarting extensions causes the current custom theme to be lost. You can reproduce by the theme stopping being purple after triggering a restart loading your example theme. Approved after that is resolved.

The other feedback is the custom themes don't seem consistent with the UI from the other themes. To remedy I would swap the order so "My Awesome Theme" shows up before the name of the extension it is from. E.g.
My Awesome theme (extension-name)
where extension name could be de-emphasized. That way they will read like other extensions but you can still see the source.

Approved after these comments are addressed.

Addresses feedback on the custom themes feature: - Fixes an issue where the active custom theme from an extension would be lost upon extension reload. is now more resilient and re-finds themes by name after they are re-registered. - Improves the display format of extension-provided themes in the theme selection dialog. The format is now with the extension name de-emphasized, making it consistent with other UI elements. - Updates the theme example to be more comprehensive ('shades of green') and corrects the instructions in the README, including the now-accurate slash command. - Removes unnecessary whitespace from the interface in .

Corrected a flawed assertion in that was checking for the default theme before the extension was disabled. It now correctly checks for the extension theme's name, resolving the test failure. This also includes the automatic update to NOTICES.txt due to preflight.

spencer426 · 2026-01-26T21:13:29Z

Restarting extensions causes the current custom theme to be lost. You can reproduce by the theme stopping being purple after triggering a restart loading your example theme. Approved after that is resolved.

The other feedback is the custom themes don't seem consistent with the UI from the other themes. To remedy I would swap the order so "My Awesome Theme" shows up before the name of the extension it is from. E.g. My Awesome theme (extension-name) where extension name could be de-emphasized. That way they will read like other extensions but you can still see the source.
Approved after these comments are addressed.

Updated and updated the pr to include the new example theme.

jacob314

…-gemini#17327)

spencer426 requested a review from a team as a code owner January 22, 2026 18:45

gemini-code-assist Bot reviewed Jan 22, 2026

View reviewed changes

gemini-cli Bot added priority/p2 Important but can be addressed in a future release. area/extensions Issues related to Gemini CLI extensions capability labels Jan 22, 2026

spencer426 force-pushed the feature/custom-themes branch from dd08323 to 5976610 Compare January 22, 2026 19:26

feat(extensions): add support for custom themes in extensions

dd57de4

This change introduces the ability for extensions to define and register custom themes. Extensions can now include a property in their file, and these themes will be loaded and made available to the user. Fixes #16192

spencer426 force-pushed the feature/custom-themes branch from 5976610 to dd57de4 Compare January 22, 2026 19:42

Merge branch 'main' into feature/custom-themes

e1ea92e

jacob314 reviewed Jan 22, 2026

View reviewed changes

spencer426 force-pushed the feature/custom-themes branch 2 times, most recently from b0baf23 to 1306f54 Compare January 23, 2026 02:19

feat: address code review comments for custom themes

92bad52

spencer426 force-pushed the feature/custom-themes branch from 1306f54 to 92bad52 Compare January 23, 2026 02:25

Merge branch 'main' into feature/custom-themes

6a09428

gemini-cli Bot added the help wanted We will accept PRs from all issues marked as "help wanted". Thanks for your support! label Jan 23, 2026

fix(cli): correct mock config for extension theme tests

c9ec1c4

The test in was failing because the provided to was missing the method. This commit adds the missing with a mocked method to the to correctly reflect the interface expected by .

spencer426 force-pushed the feature/custom-themes branch from fafe035 to c9ec1c4 Compare January 23, 2026 16:24

Merge branch 'main' into feature/custom-themes

5f204d9

spencer426 added 2 commits January 23, 2026 12:20

Merge branch 'main' into feature/custom-themes

7f3ad14

Merge branch 'main' into feature/custom-themes

33dd1e1

jacob314 reviewed Jan 23, 2026

View reviewed changes

Comment thread packages/cli/src/ui/themes/theme.ts Outdated

jacob314 reviewed Jan 23, 2026

View reviewed changes

spencer426 added 5 commits January 26, 2026 13:01

Merge branch 'main' into feature/custom-themes

d1ab25e

Merge branch 'main' into feature/custom-themes

e660329

spencer426 added 3 commits January 27, 2026 09:05

Merge branch 'main' into feature/custom-themes

127e02f

Merge branch 'main' into feature/custom-themes

3d4eafe

Merge branch 'main' into feature/custom-themes

0e7a796

jacob314 approved these changes Jan 28, 2026

View reviewed changes

spencer426 added this pull request to the merge queue Jan 28, 2026

Merged via the queue into main with commit beaa134 Jan 28, 2026
25 checks passed

spencer426 deleted the feature/custom-themes branch January 28, 2026 19:10

sidwan02 pushed a commit to sidwan02/gemini-cli-gemma that referenced this pull request Feb 6, 2026

feat(extensions): add support for custom themes in extensions (google…

1770019

…-gemini#17327)

jacob314 mentioned this pull request Feb 16, 2026

Add Support for Gruvbox Theme #19091

Closed

jackwotherspoon mentioned this pull request Feb 16, 2026

docs: custom themes in extensions #19219

Merged

kuishou68 pushed a commit to iOfficeAI/gemini-cli-pro that referenced this pull request Feb 27, 2026

feat(extensions): add support for custom themes in extensions (google…

5a43762

…-gemini#17327)

cocosheng-g pushed a commit that referenced this pull request May 6, 2026

feat(extensions): add support for custom themes in extensions (#17327)

c6f2add

sripasg added the size/l A large sized PR label Jun 2, 2026

		const tempHomeDir = fs.mkdtempSync(
		path.join(fs.realpathSync('/tmp'), 'gemini-cli-test-'),

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