Agent Skills: Implement Core Skill Infrastructure & Tiered Discovery #15698

NTaylorMullen · 2025-12-30T00:13:25Z

Summary

This PR implements the foundational infrastructure for Agent Skills in
Gemini CLI. It introduces the core discovery engine, the SkillManager service,
and the initial configuration gates required to support specialized expertise
based on the Agent Skills open standard.

Details

SkillManager Service: A new centralized service in
@google/gemini-cli-core that handles the discovery, parsing, and lifecycle
management of skills.
Tiered Discovery: Implements scanning for SKILL.md files in
~/.gemini/skills (User) and .gemini/skills (Project).
Resolution & Precedence: Establishes logic where project-tier skills
override user-tier skills of the same name.
Feature Gate: Introduces the experimental.skills setting (default
false) and the skills.disabled array for granular control. Renamed
internal flag to skillsSupport for clarity.
Metadata Parsing: Supports the standard SKILL.md format using YAML
frontmatter for skill name and description.
Linting & Quality: Uses debugLogger.debug for discovery tracing to
ensure a clean UI unless explicit debug mode is enabled.

Related Issues

Part of #15327, Fixes #15686

How to Validate

E2E Manual Verification:
- Enable the experimental feature in your settings.json (accessible via
  /settings or by editing ~/.gemini/settings.json):
```
{
  "experimental": {
    "skills": true
  }
}
```
- Create a dummy skill directory at .gemini/skills/text-expert/SKILL.md:
```
---
name: test-expert
description: A test skill for infrastructure validation.
---

# Instructions

You are a text expert.
```
- Build the project locally: npm run build
- Start the CLI with debug logging enabled: npm run start -- --debug (or
  use the VSCode "CLI (Interactive)" launch task with DEBUG=true).
- Expectation: Upon startup, check the debug output (press F12 in
  interactive mode to open the debug drawer). You should see logs confirming
  the SkillManager activity:
  - Discovering skills in: /path/to/project/.gemini/skills
  - Found 1 potential skill files in ...
  - Discovered skill: test-expert at ...

Pre-Merge Checklist

gemini-code-assist · 2025-12-30T00:13:48Z

Summary of Changes

Hello @NTaylorMullen, 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 establishes the foundational infrastructure for Agent Skills in the Gemini CLI. It introduces a new SkillManager service responsible for discovering, parsing, and managing skills from both user and project directories, with a clear precedence hierarchy. The changes also include new configuration settings to enable the experimental feature and control individual skills, providing a robust and extensible framework for integrating specialized agent capabilities.

Highlights

Core Skill Infrastructure: Introduction of the SkillManager service, a foundational component for discovering, parsing, and managing the lifecycle of Agent Skills within the Gemini CLI.
Tiered Skill Discovery: Implementation of a discovery engine that scans for SKILL.md files in both user-level (~/.gemini/skills) and project-level (.gemini/skills) directories, with project-defined skills taking precedence over user-defined ones.
Configuration and Control: New configuration settings have been added: experimental.skills to enable or disable the entire Agent Skills feature, and skills.disabled to provide granular control over individual skills.
Metadata Parsing: Support for parsing SKILL.md files, extracting skill name and description from YAML frontmatter, adhering to the Agent Skills open standard.

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gemini-code-assist

Code Review

This pull request introduces the foundational infrastructure for Agent Skills, including a new "SkillManager" service for discovering and managing skills from "SKILL.md" files, supporting tiered discovery from user and project directories with necessary configuration gates. However, the implementation introduces a critical insecure deserialization vulnerability by using the unsafe "yaml.load()" function on user-controllable "SKILL.md" files, which could allow arbitrary code execution. Additionally, a refactoring of the "SkillManager" is suggested to improve maintainability and correctness by removing redundant logic.

packages/core/src/services/skillManager.ts

github-actions · 2025-12-30T00:18:38Z

Size Change: +112 kB (+0.51%)

Total Size: 22.2 MB

Filename	Size	Change
`./bundle/gemini.js`	22.2 MB	+112 kB (+0.51%)

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}

abhipatel12

Love it! Have a few questions, lmk what you think!

packages/cli/src/config/settingsSchema.ts

packages/core/src/services/skillManager.ts

- Refactor SkillManager to handle tiered discovery internally for explicit precedence - Cache full skill content (including body) during discovery to avoid redundant parsing - Hide experimental skill settings from the dialog - Use debugLogger.log instead of .error for discovery issues to keep CLI footer clean - Centralize and unify frontmatter parsing logic Part of #15327

abhipatel12

LGTM!

packages/core/src/services/skillManager.ts

…mand) (#15699)

- Simplify skillsCommand structure and subcommand routing - Add autocomplete for skill names in enable/disable subcommands - Gate /skills command on experimental.skills setting - Add snapshot tests for SkillsList component - Refactor subcommand actions into helper functions - Rename getSkillContent to getSkill and use it in skillsCommand Part of #15698

abhipatel12

Looks great!

NTaylorMullen requested review from a team as code owners December 30, 2025 00:13

feat(skills): implement foundational infrastructure and feature gate

d707f3d

NTaylorMullen force-pushed the ntm/skills.1 branch from 4f4ae18 to d707f3d Compare December 30, 2025 00:15

gemini-code-assist bot reviewed Dec 30, 2025

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abhipatel12 approved these changes Dec 30, 2025

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NTaylorMullen added 2 commits December 30, 2025 14:32

Agent Skills: Implement Interactive Management Interface (/skills com…

f8a3ea6

…mand) (#15699)

abhipatel12 approved these changes Dec 30, 2025

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Agent Skills: Implement Core Skill Infrastructure & Tiered Discovery #15698

Agent Skills: Implement Core Skill Infrastructure & Tiered Discovery #15698

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Summary

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Related Issues

How to Validate

Pre-Merge Checklist

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