Level 3: Builder — Automate Repetition with Custom Skills

Typing the same instructions every time is inefficient. Having to type “Please review this code. Consider bugs, performance, and type definitions…” every time you want a code review is the Level 2 way of working. With custom slash commands, a single /review executes those instructions.

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How Custom Slash Commands Work

In Claude Code, you can create your own slash commands by placing Markdown files in the .claude/commands/ folder.

your-project/
├── .claude/
│   ├── settings.json
│   └── commands/
│       ├── review.md      → callable with /review
│       └── changelog.md   → callable with /changelog
└── CLAUDE.md

The contents of the Markdown file become the command’s instructions. The filename becomes the command name (review.md → /review).

Command Example 1: /review (Code Review)

.claude/commands/review.md:

# Code Review

Check the current diff (git diff) and review from the following perspectives:

1. **Potential bugs** — null references, boundary errors, missing exception handling
2. **Performance** — N+1 queries, unnecessary loops, memory leaks
3. **Type consistency** — missing type definitions, implicit type conversions
4. **Security** — SQL injection, authentication, input validation

## Output Format

List issues in the format "Severity (High/Medium/Low): filename — description."
If there are no issues, respond with "Review complete: no issues."

How to invoke:

/review

Command Example 2: /changelog (Release Note Generation)

.claude/commands/changelog.md:

# Release Note Generation

Check the recent commit history with `git log --oneline` and generate release notes in the following format.

## Output Format

```markdown
## [Version] - YYYY-MM-DD

### New Features
- [Summarize feat commits]

### Bug Fixes
- [Summarize fix commits]

### Other
- [Summarize chore/refactor/docs commits]

Constraints

• Rephrase commit messages in terms that non-engineers can also understand
• Group internal refactoring and CI changes under “Other”

How to invoke:

/changelog

## Receiving Arguments with $ARGUMENTS

When you want to pass arguments to a command, use `$ARGUMENTS` inside the Markdown file.

`.claude/commands/fix.md`:

```markdown
# Bug Fix

Please fix the following bug:

$ARGUMENTS

## Steps

1. First write a test case that reproduces the bug
2. Confirm the test fails
3. Fix the bug
4. Confirm the test passes
5. Update related documentation and comments

How to invoke:

/fix GET /users/{id} returns 500 when user does not exist

“GET /users/{id} returns 500 when user does not exist” is passed into the $ARGUMENTS placeholder.

Regular Instructions vs. Custom Skills

Item	Regular instructions	Custom skills
How to invoke	Type out text every time	A single /command-name
Consistency	Tends to vary between sessions	Same instructions executed every time
Team sharing	Difficult	Git-manage .claude/commands/ and everyone can use them
Passing arguments	Write an explanation every time	Just append after $ARGUMENTS

By managing the .claude/commands/ folder with git, the whole team can use the same commands.

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Hands-On Tutorial

If you want to learn by doing, check out the tutorial.

Hands-on tutorial for this level →

Next Level

Level 4: Context Engineer — Design Memory and Context

See the references for the external specifications and background sources used on this page.[1][2]

References

1. Anthropic, Claude Code documentation
2. Anthropic, Claude API documentation