Why Http request with Fiddler is blazing fast

Question

I wrote a multithread program in c# that crawls a web site, but when I started Fiddler in the background request completed 12x faster, it is really strange for me and when I

Answer 1

Can you show some sample code so people can confirm this? Otherwise it'll become wild guessing.

My best guess: Fiddler uses keepalive which will save the trouble of opening the connection over and over again. You can confirm this by disabling both Reuse client connections and Reuse connections to servers: if it's then as slow as usual (or slower), the benefit is gained from keeping the connection alive.