Fiddler Ideas

The free web debugging proxy for any browser, system or platform.

400 Bad Request


#!/usr/bin/env python3
from urllib.request import urlopen

# with fiddler open
# no problem, see the slash
resp = urlopen("")

# with fiddler open
# raises 400 Bad Request
resp = urlopen("")

# with fiddler close
# no problem
resp = urlopen("")


see wireshark.png



v5.0.20181.14850 for .NET 4.6.1
64-bit AMD64, VM: 47.0mb, WS: 87.0mb
.NET 4.6.2 WinNT 10.0.17134.0

  • Guest
  • Jun 1 2018
  • Under review
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  • Eric Lawrence commented
    5 Jun, 2018 04:03pm

    In Fiddler, you should have received a HTTP protocol warning noting that URLs require a trailing slash after the hostname (meaning, a non-empty path component). Per the HTTP specification, clients should be adding such a slash (Python apparently does not) and servers absolutely need to be treating such requests equivalently whether the slash is present or not.