Reading & Editing Files

File manipulation is the core of what Claude Code does. Understanding how it reads and writes files will make you a much more effective user.

How Claude Reads Files

Claude has several tools for understanding your codebase:

Read Tool

Reads a specific file by path. Claude uses this when it knows exactly which file to look at.

> What's in my package.json?

Claude will call Read("package.json") and show you the contents.

Glob Tool

Finds files matching a pattern. Used when Claude needs to discover files.

> Find all TypeScript files in the src directory

Claude calls Glob("src/**/*.ts") to find matches.

Grep Tool

Searches file contents with regex. Used when Claude needs to find specific code.

> Where is the database connection configured?

Claude might call Grep("database|connection|DB_HOST") across your project.

How Claude Edits Files

Write Tool

Creates new files or completely replaces existing ones.

> Create a new utils/helpers.ts file with a slugify function

Edit Tool

Makes targeted changes to existing files. This is the most common editing operation — Claude identifies the exact string to replace and swaps it.

> Change the primary color from blue to red in the CSS

Claude will:

1. Read the file
2. Find the exact line(s) to change
3. Show you the diff
4. Apply the change on your approval

The @ Symbol

You can reference files directly with @:

> Look at @src/components/Header.tsx and make the nav responsive

This is a hint to Claude about which file to focus on. It’s especially useful when:

• Your project is large and you want to direct attention
• The file name is ambiguous
• You want Claude to read it before you ask your question

Best Practices

Let Claude Read First

Don’t ask Claude to modify code it hasn’t seen. Always let it read the current state:

# Good
> Read @src/api/auth.ts and then add rate limiting to the login endpoint

# Less good
> Add rate limiting to the login endpoint in src/api/auth.ts

The second version works, but Claude will read it anyway — being explicit sets clearer expectations.

Review Diffs Carefully

Claude’s Edit tool shows you exactly what’s changing. Take a moment to review:

• Is it changing the right file?
• Is the replacement correct?
• Are there side effects?

Use Multi-File Operations

Claude can work across multiple files in a single response:

> Rename the "users" API endpoint to "members" across all files

Claude will grep for references, then edit each file in sequence.

Exercise

1. Create a new project directory
2. Ask Claude to create a simple Express.js API with two endpoints
3. Ask Claude to add a third endpoint
4. Ask Claude to refactor the routes into a separate file
5. Watch how it reads, creates, and edits files throughout