g3/docs/skills.md

Agent Skills Guide

Last updated: February 2025
Source of truth: crates/g3-core/src/skills/, skills/

Purpose

This document describes g3's Agent Skills system - a mechanism for extending agent capabilities through portable skill packages. Skills allow g3 to learn new abilities without code changes.

Overview

g3 implements the Agent Skills specification, an open format for portable skill packages. Each skill is a directory containing:

• SKILL.md - Skill definition with YAML frontmatter and instructions
• scripts/ (optional) - Executable scripts the skill can use
• references/ (optional) - Additional documentation
• assets/ (optional) - Templates, data files, etc.

At startup, g3 discovers skills from multiple locations and injects a summary into the system prompt. When the agent needs a skill, it reads the full SKILL.md using the read_file tool.

Quick Start

Using Existing Skills

Skills are automatically discovered. To see available skills, check the system prompt or look in:

# Global skills (shared across all projects)
ls ~/.g3/skills/

# Workspace skills (project-specific)
ls .g3/skills/

# Repo skills (checked into git)
ls skills/

Creating a New Skill

1. Create a skill directory:

   mkdir -p skills/my-skill
   

2. Create SKILL.md with frontmatter:

   ---
   name: my-skill
   description: Brief description of what this skill does and when to use it.
   license: MIT
   compatibility: Any requirements (e.g., "Requires Python 3.8+")
   ---
   
   # My Skill
   
   Detailed instructions for the agent...
   

3. The skill is now available to g3.

SKILL.md Format

Frontmatter (Required)

The YAML frontmatter between --- markers defines skill metadata:

---
name: skill-name          # Required: 1-64 chars, lowercase + hyphens only
description: What it does # Required: 1-1024 chars, when to use this skill
license: Apache-2.0       # Optional: SPDX license identifier
compatibility: Requires X # Optional: Environment requirements (max 500 chars)
metadata:                 # Optional: Arbitrary key-value pairs
  author: your-org
  version: "1.0"
---

Name validation rules:

• 1-64 characters
• Lowercase letters, numbers, and hyphens only
• Must start with a letter
• No consecutive hyphens

Body (Instructions)

After the frontmatter, write detailed instructions for the agent:

# Skill Title

## Quick Start
How to use this skill in the simplest case.

## Detailed Usage
Step-by-step instructions, examples, edge cases.

## Troubleshooting
Common issues and solutions.

Best practices:

• Keep the description concise (it's shown in the skill summary)
• Put detailed instructions in the body (only loaded when needed)
• Include concrete examples
• Document error handling

Discovery Priority

Skills are discovered from multiple locations. Higher priority sources override lower ones:

Priority	Location	Use Case
1 (lowest)	Embedded	Core skills compiled into binary
2	~/.g3/skills/	Global user skills
3	Config extra_paths	Organization-wide skills
4	.g3/skills/	Workspace-local customizations
5 (highest)	skills/	Repo skills (checked into git)

Override behavior: If the same skill name exists in multiple locations, the highest priority version wins. This allows:

• Customizing embedded skills per-project
• Testing skill changes without modifying global installs
• Sharing skills across an organization via config paths

Configuration

Skills can be configured in ~/.config/g3/config.toml or ./g3.toml:

[skills]
enabled = true                    # Default: true
extra_paths = [                   # Additional skill directories
  "/org/shared/skills",
  "~/my-skills"
]

To disable skills entirely:

[skills]
enabled = false

Embedded Skills

Core skills are embedded into the g3 binary at compile time, ensuring they work anywhere without external files.

Currently Embedded Skills

Skill	Description
research	Web-based research via scout agent with browser automation

How Embedding Works

Embedded skills use Rust's include_str! macro to compile SKILL.md and scripts into the binary:

// Currently empty - skills can be added here as needed
static EMBEDDED_SKILLS: &[EmbeddedSkill] = &[
    // Example of how to add an embedded skill:
    // EmbeddedSkill {
    //     name: "example-skill",
    //     skill_md: include_str!("../../../../skills/example-skill/SKILL.md"),
    // },
];

Script Extraction

Embedded scripts are extracted to .g3/bin/ on first use:

1. First run: Script is written to .g3/bin/<script-name>
2. Permissions: Made executable (chmod 755 on Unix)
3. Version tracking: Content hash stored in .g3/bin/<script-name>.version
4. Updates: Re-extracted automatically when embedded version changes

This ensures:

• Scripts are always available, even in fresh workspaces
• Updates propagate automatically when g3 is upgraded
• No manual installation required

Creating Skills with Scripts

Skills can include executable scripts for complex operations:

Script Location

Place scripts in the skill directory:

skills/my-skill/
├── SKILL.md
├── my-script.sh        # Bash script
├── helper.py           # Python script
└── scripts/
    └── complex-tool    # Subdirectory also works

Referencing Scripts

In SKILL.md, reference scripts relative to the skill directory:

## Usage

Run the helper script:
```bash
shell("skills/my-skill/my-script.sh arg1 arg2")

### Embedding Scripts

To embed scripts in the binary (for core skills), add them to `embedded.rs`:

```rust
EmbeddedSkill {
    name: "my-skill",
    skill_md: include_str!("../../../../skills/my-skill/SKILL.md"),
    scripts: &[
        ("my-script", include_str!("../../../../skills/my-skill/my-script.sh")),
    ],
},

Context Budget

Each skill adds approximately 50-100 tokens to the system prompt (name + description + path). The full SKILL.md body is only loaded when the agent reads it.

Recommendations:

• Keep descriptions under 200 characters
• Put detailed instructions in the body, not the description
• Avoid creating many small skills; consolidate related functionality

Troubleshooting

Skill Not Discovered

1. Check the skill directory exists and contains SKILL.md
2. Verify the frontmatter is valid YAML
3. Ensure name and description fields are present
4. Check for syntax errors in the YAML (use a YAML validator)

Skill Overridden Unexpectedly

Skills with the same name are overridden by higher-priority sources. Check:

• skills/ (repo) overrides everything
• .g3/skills/ (workspace) overrides global and embedded
• ~/.g3/skills/ (global) overrides embedded only

Embedded Script Not Found

If .g3/bin/<script> doesn't exist:

1. The skill may not have been used yet (extraction is lazy)
2. Check permissions on .g3/bin/ directory
3. Try deleting .g3/bin/<script>.version to force re-extraction

Adding a New Embedded Skill

To add a new skill to the g3 binary:

1. Create the skill in skills/<name>/:

   skills/new-skill/
   ├── SKILL.md
   └── optional-script.sh
   

2. Add to crates/g3-core/src/skills/embedded.rs:

   EmbeddedSkill {
       name: "new-skill",
       skill_md: include_str!("../../../../skills/new-skill/SKILL.md"),
       scripts: &[
           ("optional-script", include_str!("../../../../skills/new-skill/optional-script.sh")),
       ],
   },
   

3. Rebuild g3:

   cargo build --release
   

See Also

• Agent Skills Specification - The open standard
• Architecture: Skills System - Internal implementation
• README: Agent Skills - Quick overview