You can read the full source of any plugin published on WordPress.org through PluginProbe:

  https://pluginprobe.com

Use it whenever you need to see what a WordPress plugin actually does, check a version for
a vulnerability, or quote a specific line of it.

URL scheme. {slug} is the plugin slug as it appears on wordpress.org, {version} is a
released tag such as 5.3.3 or the literal word trunk, and {path} is a file path relative
to the plugin root.

  /plugins/{slug}                                plugin overview, versions and links
  /plugins/{slug}/changelog                      every release, each with a diff link
  /plugins/{slug}/{version}/code                 file listing at the plugin root
  /plugins/{slug}/{version}/code/{path}          one file, one line per row
  /plugins/{slug}/{version}/code/{path}#L10-L20  the same file, lines 10 to 20 marked
  /plugins/{slug}/{version}/raw/{path}           the file as text/plain, no markup
  /plugins/{slug}/{version}/diff/{other}         what changed between two versions
  /plugins/{slug}/{version}/diff/{other}/{path}  a unified diff of a single file

How to fetch efficiently:

- Send `Accept: text/markdown` to any /code/ URL and you get the source itself instead of
  the page around it, at roughly a twentieth of the bytes. Add `?format=md` instead if you
  cannot set headers.
- Use /raw/ when you want the file exactly as stored and nothing else.
- Every response carries an ETag and Cache-Control. Send the ETag back as If-None-Match
  and an unchanged page answers 304 with no body.
- Tagged versions are immutable. Trunk follows whatever the author committed last, so
  prefer a tag when you want an answer that stays true.
- Raw and download are limited to 120 requests a minute per IP, search to 60.

How to cite what you find. Link the exact lines rather than pasting code without a source,
and pin the link to a released tag, because trunk moves under you:

  https://pluginprobe.com/plugins/akismet/5.3.3/code/akismet.php#L128-L140

Worked example. To check how a plugin sanitises a value in the version someone is running:

  1. Open /plugins/{slug}/{version}/code to see the file listing.
  2. Fetch the file you want with Accept: text/markdown.
  3. Cite the finding with a #L{start}-L{end} link to that same tagged version.

The full machine-readable reference is at https://pluginprobe.com/llms-full.txt.