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Skills

Skills are discoverable instruction packs that extend nca's agent behavior. Each skill is a SKILL.md file that teaches the agent how to handle specific tasks, frameworks, or workflows.

How Skills Work

Skills are not code plugins — they are structured instruction documents that the agent loads into its context when relevant. When a skill is invoked, the agent reads the skill's SKILL.md and follows its instructions.

Skill Discovery

nca looks for skills in configured directories:

[harness]
skill_directories = [".nca/skills", ".claude/skills"]

Default search paths (relative to workspace):

  1. .nca/skills/ — nca-specific skills
  2. .claude/skills/ — compatible with Claude Code skills

Skill Structure

Each skill is a directory containing a SKILL.md file:

.nca/skills/
├── rust-patterns/
│   └── SKILL.md
├── api-design/
│   └── SKILL.md
└── testing/
    └── SKILL.md

Managing Skills

List Skills

nca skills                    # List all discovered skills
nca skills list               # Same
nca skills list --json        # JSON output

Or in interactive mode:

/skills

Install Skills

# Install from a remote source
nca skills add https://github.com/user/skill-repo

# Install specific skills from a source
nca skills add https://github.com/user/skill-repo -s rust-patterns -s testing

# Install globally (available in all workspaces)
nca skills add https://github.com/user/skill-repo --global

Remove Skills

nca skills remove rust-patterns
nca skills remove rust-patterns --global

Update Skills

nca skills update                # Update all skills
nca skills update rust-patterns  # Update a specific skill

Using Skills

Automatic Discovery

The agent's system prompt includes a list of available skills. The agent can choose to invoke relevant skills based on the task.

Explicit Invocation

Ask the agent to use a skill:

Use the rust-patterns skill to review this code.

Or the agent can invoke skills programmatically via the invoke_skill tool.

Slash Command

/skills                    # List available skills

Writing Skills

SKILL.md Format

Create a SKILL.md file in a skill directory:

# Skill Name

Brief description of what this skill does.

## When to Use

Describe when this skill should be activated.

## Instructions

Step-by-step instructions for the agent to follow.

### Step 1: Analysis

Analyze the codebase for...

### Step 2: Implementation

Apply the following patterns...

## Examples

### Before
\`\`\`rust
// problematic code
\`\`\`

### After
\`\`\`rust
// improved code
\`\`\`

Best Practices

  1. Be specific — give clear, actionable instructions the agent can follow
  2. Include examples — show before/after code when applicable
  3. Define scope — explain when the skill should and shouldn't be used
  4. Keep it focused — one skill per concern (don't combine testing and deployment)
  5. Use structured steps — numbered steps help the agent track progress

Skill Directories

Workspace Skills

my-project/.nca/skills/my-skill/SKILL.md

Available only in this workspace. Good for project-specific conventions.

Global Skills

~/.nca/skills/my-skill/SKILL.md

Available in all workspaces. Good for personal coding standards and reusable patterns.

Claude-Compatible Skills

my-project/.claude/skills/my-skill/SKILL.md

nca discovers skills from .claude/skills/ by default, making it compatible with Claude Code skill conventions.

System Prompt Integration

When skills are available, nca adds a skills section to the system prompt listing all discovered skills by name. The agent can then use the invoke_skill tool to load any skill's full instructions on demand.