Most pages on GitHub support keyboard shortcuts. To see the shortcuts, just click ? on any GitHub page.
So, if you are looking at a specific commit, you will see several keyboard shortcuts available (in the Browsing Commits section), including: p for parent commit . So, when you are on a specific commit, press p and you will go to the previous (parent) commit. Unfortunately, I do not see a shortcut to go to the next (child) commit.
Also note that all commit pages have links to a parent located near the top of the page (look for txt "1 parent" with a short SHA that will be a link to the parent commit).
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