See what changed in a file

Agents: claude, codex, opencode · On: phone, desktop

The open file is marked with what has changed since the last commit: new lines are highlighted, and lines that were taken out stand where they used to be.

Why you would use it

The agent has edited a file and you want to read the result in context, not as a patch. The marks show the change against the file as it is now, so the lines around it are the real ones.

How to use it

Open a file from the explorer.
The marks are already on, if the file has changed.
Tap the diff button in the viewer head (#viewer-diff, "Show changes since the last commit") to turn the marks off, and again to turn them back on.

What you see

Added lines are highlighted on the line itself.
Removed lines are inserted above the line they were taken out from, with − in the number column instead of a number. Lines removed past the end of the file stand after the last line.
Removed lines are coloured as code in the file's language, lexed as their own run.
An untracked file is marked new on every line.
With the marks off, the file reads as plain text; the button's pressed state (aria-pressed) follows.

Options and settings

Option	Default	What it changes
`#viewer-diff`	on	Marks on or off. Kept for the session and applied to the next file you open, not stored

Limits and known gaps

The comparison is with the last commit (HEAD), including staged and unstaged edits. It is not "what this turn changed" — for that, see turn-changes.
In a repository with no commit yet, everything counts as added.
Outside a git repository there are no marks at all.
A removed line cannot be commented on: it is not a line of the file as it is now, so tapping it does nothing.
The added lines are not sent over the wire — the viewer already holds the file as it is now and only needs to know which of its lines are new.
The diff button shows on every file, even one with nothing changed in it. fillViewer() sets hidden on it, but .icon-btn in public/styles.css carries display: inline-flex, which wins over the hidden attribute. On a file with no marks, tapping it changes nothing on screen.