For running clang-format there is: scripts/run_clang_format.sh.

Are you aware that something like this would also wok:
(constructing a CurlHolder() is compatibly expensive)

Wasn't aware of that - it feels a bit wrong to do as well but i can see how that would have been easier 😅

I'll get into the tests & docs :)

Running the clang-format script i get following changed files:

On branch muxelplexer/getcontent
Your branch is up to date with 'origin-mux/muxelplexer/getcontent'.

Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
        modified:   cpr/connection_pool.cpp
        modified:   test/abstractServer.hpp
        modified:   test/connection_pool_tests.cpp
        modified:   test/proxy_tests.cpp

Can add the formatting of those into this MR but none of them should belong to my changes.