In Level 3 you got comfortable asking Claude about code — what does this do, where is that defined, why is it written this way. This level is the next move: asking Claude to change code.
When Claude wants to change a file, it proposes the change first as a visual diff in the preview pane. You see it. You click Accept or Reject. The file doesn’t move until you accept.
That single rule is the foundation of every later lesson in this level. Hold onto it.
What an edit actually looks like
You ask for something specific, right in the chat:
Claude reads the file, figures out the change, and then pauses — it shows you the change in the preview pane. Not a paragraph describing the change, but the actual line-by-line difference between what’s there now and what it wants to put there, with the old in red and the new in green. That difference is called a diff, and the next lesson is all about reading one.
You either Accept it or you Reject it. Nothing touches the file until you click.
Tourist vs collaborator
In Level 3 you were a tourist. You walked around a codebase asking questions. Nothing you said could break anything — the worst that could happen was a wrong answer.
This level is different. You’re now editing real files. The blast radius is real.
But notice what isn’t different: Claude still doesn’t change anything without your approval. That gate is always there — now it’s a button you click, not a guess you make. The work changes; the trust model doesn’t.
About the permission prompt
You’ll see the permission prompt (from Lesson 1.6) every time Claude wants to write to a file in this level. For now: read what it shows you, click Accept if it looks right, move on.
Level 5 is the whole story of when to widen that gate, when to keep it narrow, and what to never allow without thinking. For this level, default mode. One change at a time. Accept once.
What’s next
Claude is going to show you diffs constantly from here on. The next lesson is the actual reading — what the green and red lines mean, what context lines are, and why scanning a diff is not the same as reading one.