Command Development

# Command Development for Claude Code

## Overview

Slash commands are frequently-used prompts defined as Markdown files that Claude executes during interactive sessions. Understanding command structure, frontmatter options, and dynamic features enables creating powerful, reusable workflows.

**Key concepts:**
- Markdown file format for commands
- YAML frontmatter for configuration
- Dynamic arguments and file references
- Bash execution for context
- Command organization and namespacing

## Command Basics

### What is a Slash Command?

A slash command is a Markdown file containing a prompt that Claude executes when invoked. Commands provide:
- **Reusability**: Define once, use repeatedly
- **Consistency**: Standardize common workflows
- **Sharing**: Distribute across team or projects
- **Efficiency**: Quick access to complex prompts

### Critical: Commands are Instructions FOR Claude

**Commands are written for agent consumption, not human consumption.**

When a user invokes `/command-name`, the command content becomes Claude's instructions. Write commands as directives TO Claude about what to do, not as messages TO the user.

**Correct approach (instructions for Claude):**
```markdown
Review this code for security vulnerabilities including:
- SQL injection
- XSS attacks
- Authentication issues

Provide specific line numbers and severity ratings.
```

**Incorrect approach (messages to user):**
```markdown
This command will review your code for security issues.
You'll receive a report with vulnerability details.
```

The first example tells Claude what to do. The second tells the user what will happen but doesn't instruct Claude. Always use the first approach.

### Command Locations

**Project commands** (shared with team):
- Location: `.claude/commands/`
- Scope: Available in specific project
- Label: Shown as "(project)" in `/help`
- Use for: Team workflows, project-specific tasks

**Personal commands** (available everywhere):
- Location: `~/.claude/commands/`
- Scope: Available in all projects
- Label: Shown as "(user)" in `/help`
- Use for: Personal workflows, cross-project utilities

**Plugin commands** (bundled with plugins):
- Location: `plugin-name/commands/`
- Scope: Available when plugin installed
- Label: Shown as "(plugin-name)" in `/help`
- Use for: Plugin-specific functionality

## File Format

### Basic Structure

Commands are Markdown files with `.md` extension:

```
.claude/commands/
├── review.md           # /review command
├── test.md             # /test command
└── deploy.md           # /deploy command
```

**Simple command:**
```markdown
Review this code for security vulnerabilities including:
- SQL injection
- XSS attacks
- Authentication bypass
- Insecure data handling
```

No frontmatter needed for basic commands.

### With YAML Frontmatter

Add configuration using YAML frontmatter:

```markdown
---
description: Review code for security issues
allowed-tools: Read, Grep, Bash(git:*)
model: sonnet
---

Review this code for security vulnerabilities...
```

## YAML Frontmatter Fields

### description

**Purpose:** Brief description shown in `/help`
**Type:** String
**Default:** First line of command prompt

```yaml
---
description: Review pull request for code quality
---
```

**Best practice:** Clear, actionable description (under 60 characters)

### allowed-tools

**Purpose:** Specify which tools command can use
**Type:** String or Array
**Default:** Inherits from conversation

```yaml
---
allowed-tools: Read, Write, Edit, Bash(git:*)
---
```

**Patterns:**
- `Read, Write, Edit` - Specific tools
- `Bash(git:*)` - Bash with git commands only
- `*` - All tools (rarely needed)

**Use when:** Command requires specific tool access

### model

**Purpose:** Specify model for command execution
**Type:** String (sonnet, opus, haiku)
**Default:** Inherits from conversation

```yaml
---
model: haiku
---
```

**Use cases:**
- `haiku` - Fast, simple commands
- `sonnet` - Standard workflows
- `opus` - Complex analysis

### argument-hint

**Purpose:** Document expected arguments for autocomplete
**Type:** String
**Default:** None

```yaml
---
argument-hint: [pr-number] [priority] [assignee]
---
```

**Benefits:**
- Helps users understand command arguments
- Improves command discovery
- Documents command interface

### disable-model-invocation

**Purpose:** Prevent SlashCommand tool from programmatically calling command
**Type:** Boolean
**Default:** false

```yaml
---
disable-model-invocation: true
---
```

**Use when:** Command should only be manually invoked

## Dynamic Arguments

### Using $ARGUMENTS

Capture all arguments as single string:

```markdown
---
description: Fix issue by number
argument-hint: [issue-number]
---

Fix issue #$ARGUMENTS following our coding standards and best practices.
```

**Usage:**
```
> /fix-issue 123
> /fix-issue 456
```

**Expands to:**
```
Fix issue #123 following our coding standards...
Fix issue #456 following our coding standards...
```

### Using Positional Arguments

Capture individual arguments with `$1`, `$2`, `$3`, etc.:

```markdown
---
description: Review PR with priority and assignee
argument-hint: [pr-number] [priority] [assignee]
---

Review pull request #$1 with priority level $2.
After review, assign to $3 for follow-up.
```

**Usage:**
```
> /review-pr 123 high alice
```

**Expands to:**
```
Review pull request #123 with priority level high.
After review, assign to alice for follow-up.
```

### Combining Arguments

Mix positional and remaining arguments:

```markdown
Deploy $1 to $2 environment with options: $3
```

**Usage:**
```
> /deploy api staging --force --skip-tests
```

**Expands to:**
```
Deploy api to staging environment with options: --force --skip-tests
```

## File References

### Using @ Syntax

Include file contents in command:

```markdown
---
description: Review specific file
argument-hint: [file-path]
---

Review @$1 for:
- Code quality
- Best practices
- Potential bugs
```

**Usage:**
```
> /review-file src/a