The Read / Edit / Write Loop

Claude Code never silently rewrites your files from memory. It changes code through a disciplined cycle of three built-in tools: Read, Edit, and Write.

This loop exists for one reason: safety. The model only edits text it has actually loaded, so changes are grounded in the real file on disk, not in a hallucinated version of it.

In this lesson you will learn how each tool behaves, when Claude picks one over another, and the failure modes the exam expects you to recognize.

Claude Code ships with a small, deliberate set of file tools. Each has a sharp purpose:

• Glob — find files by pattern, e.g. **/*.test.tsx
• Grep — search file contents
• Read — load one file into context
• Edit — make a precise, unique-match change
• Write — create a file (or fully replace one)
• Bash — run shell commands

The write loop is the heart of this set: you Read to ground, then Edit or Write to change.