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Reviewing Diffs

Using the Diff Viewer

Diffs can be reviewed in the Review Board diff viewer by clicking View Diff on the review request action bar.

Parts of the Diff Viewer

When you load the Diff Viewer, the page is divided into several parts:

  1. The review request box (for reference).
  2. The current diff revision and revision selector (if more than one revision of the diff has been uploaded).
  3. The file listing.
  4. The side-by-side diff for each file.

Depending on the number of files modified, the diff viewer may be split across multiple pages. You can jump to the pages using the paginator above or below the diffs.

The File Index

Changed in version 2.0.

The file index is a list of all the files which are shown on the current page. There are several parts to this display:

  • On the left is a graph which shows the ratio of added/changed/deleted lines. The thickness of this graph indicates what percentage of the file has been altered.
  • The name of the file. This can be clicked to jump directly to the diff for that file.
  • Whether the file was renamed, and the old filename if so.
  • Indications for deleted or binary files.
  • A list of clickable chunk dots, color-coded to represent add/change/delete.

Viewing Other Diff Revisions

Changed in version 2.0: The diff revision selector used to use two rows of revisions that could be clicked to jump to various revisions or interdiffs. Please see older versions of the user manual if you’re running a version of Review Board prior to 2.0.

Every public revision of a diff that was posted is available for review. The diff revision selector allows you to look at previous versions of the change. To browse old revisions, set the handle on the left to orig (meaning the original version of the file) and the handle on the right to the revision you want to look at.

This is sometimes useful when you’re in the middle of a review of a particular diff, go away for a bit, and then come back to discover that a new diff revision has been uploaded. In this case, a warning box will appear telling you that you have additional comments on an older revision, with a helpful link to jump back to that revision.


The diff viewer also allows you to do comparisons between diff revisions (called interdiffs). In other words, it lets you see what changes the developer has made since the previous version of the diff you looked at, which is very useful for large changes which require several iterations of review.

To view an interdiff between two diff revisions, set the two handles to the revisions you want to compare.


Due to the way that the diff viewer works, if a newer diff is based on a newer revision of a file, you may see other changes made to that file between those revisions that has nothing to do with the review itself.

If you’re a developer posting code and you want to sync your source tree, it’s best to try to keep as many revisions of your change based on the same revision of the source tree as possible, in order to minimize the impact of this on your reviewers.

Diff Viewer Features

Side-by-side Diffs

Diffs are displayed using a side-by-side format. This means that the old version of the file is displayed on the left, and the new version of the file is displayed on the right. The differences between the two versions are highlighted using colors: green for added lines, red for removed lines, and yellow for changed lines.

Moved Line Indicators

If you move one or more lines of code within a file, instead of just showing those lines as deleted from one location and added to another, Review Board will detect that the lines have been moved and show an indicator. These indicators can be clicked to jump to the other end of the move.


Indentation Change Indicators

New in version 2.0.

Historically, Review Board would show lines that differed only in their indentation as being equal. This is nice in most cases, but can hide important information, especially in languages like Python where the indentation is crucial to the meaning of the code.

Review Board will now show indentation changes with small indicators at the beginning of the line. Dedents will be shown on the left-hand side of the diff, and indents will be shown on the right.


Intra-line Change Highlighting

Edits which change only one or two characters in a long line can be difficult to read, so when the original and new lines are very similar, Review Board will highlight which characters changed. This is shown with a slightly darker yellow background.

Commenting on Lines

To comment on a line on a diff, simply click the line number. A comment dialog will appear giving you a text entry for writing your comment. When you’re done, you can click Save to save the comment.

Furthermore you can assign a comment to multiple code lines. This option is especially useful to provide additional code context to discussions as all commented code will appear on the review request page.

To create a multiple line comment click and drag on the beginning line number down the column until you’ve selected all the lines needed for your comment.


Comments support rich text using the Markdown language. See Using Markdown for more information.

The diff comment dialog supports issue tracking. See the section on Issue Tracking for more information.

After saving a comment, a green comment flag will appear next to the first line in your selection, indicating that you have an unpublished comment. Click the line number or comment flag to pop open the comment box for your existing comment again.

Reading Existing Comments

Any existing comments will show up as blue clickable comment flags along the left-hand side of the diff viewer. Each comment flag corresponds to a line containing a comment.

If you move the mouse cursor over the comment flag, a tooltip will appear showing a summary of the comments made.

If you click on the comment flag or the line number, the comment dialog will appear, along with a blue side panel on the left showing those existing comments. You can still write new comments in the green area of the comment box.



It’s important to note that this is not the place to reply to those comments. When you add a comment from the diff viewer, it’s creating a new top-level review (akin to a new thread). If you want to reply to existing comments, you can do so from the Reviews page. The Reply link here is a shortcut to jump directly to the relevant comment on the Reviews page.

The view here is meant to be used only as a reference to see if other people have already said what you plan to say.

Keyboard Shortcuts

There are many keyboard shortcuts for navigating around the diff viewer:

  • Previous file: a, A, K, P:, <, or m
  • Next file: f, F, J, N, >
  • Previous change: s, S, k, p, ,
  • Next change: d, D, j, n, .
  • Previous comment: [, x
  • Next comment: ], c
  • Add comment to selected block: r, R