Your first real change

So far you’ve only asked questions. Asking questions is safe — the worst case is a wrong answer you notice later. This page is the first thing you do that leaves a mark.

When Claude wants to change a file, it shows you the change first, as a diff in the preview pane. You click Accept or Reject. The file doesn’t move until you click.

Hold onto that sentence. Everything else about editing follows from it.

Ask for one specific thing

Be specific and small. In the chat:

In notes.md, change the heading from "Untitled" to "Q3 planning".

Claude reads the file, works out the change, and then stops. The preview pane lights up with the before and after: the old line in red, the new line in green.

Read the diff

That pane is now the most important thing on your screen.

 # Meeting notes
-## Untitled
+## Q3 planning

Three lines, and only two of them are changing. The plain line at the top is context — it’s there to show you where in the file you are. The red line is being removed. The green line is being added.

That’s the entire vocabulary. Green adds, red removes, plain lines are just showing you the neighbourhood.

Scanning is not reading

Most people glance at a diff, see roughly the right words in roughly the right colours, and click Accept. That’s nodding, not reading.

Claude can be confidently wrong. It can rename something correctly in five places and miss the sixth. It can make the change you asked for and quietly fix a typo you didn’t mention. The diff shows you all of it.

When a diff runs past ten or fifteen lines, slow down. Go line by line and ask one question: did I ask for this? If the answer is no, Reject is right there, and nothing has happened yet.

Don’t read the summary, read the diff

Claude will usually describe the change in the chat, above the diff — “I’ve updated the heading in notes.md.” That sentence is interpretation. The diff is reality.

Sometimes they match exactly. Sometimes the diff also moved a line, or removed something you didn’t ask about. The summary won’t always mention it.

Read the diff. Every time. The chat message is a hint; the diff is the contract, and it isn’t signed until you click Accept.