See the PDF, not just the diff.

TeXPRs compiles the LaTeX in a GitHub pull request and shows the PDF before and after, side by side, overlaid, or with every change marked up. No cloning, no checking out branches.

Or swap github.com for texprs.com in any pull request link:

github.com/owner/repo/pull/12
texprs.com/owner/repo/pull/12