What does the 'X-DevTools-Emulate-Network-Conditions-Client-Id' header key represent?

Question

I see this key in requests occasionally when I have devtools open, but not always.

Answer 1

It's a header that Chrome devtools uses internally to let chrome know they're emulating a slow network/device. Chrome, in turn, should however not send this header in actual network requests. It appears this did happen in the past though (maybe even present).

See the bug here: https://bugs.chromium.org/p/chromium/issues/detail?id=395966