Fiddler CLI Command Reference

This article lists the built-in commands of the Fiddler CLI and shows how to use them.

Commands are case-insensitive. Arguments are positional—pass values directly after the command name, without option names.

Commands

Any other command name is forwarded to the OnCliCommand handler of the active script. For details, see Custom CLI Commands.

Capture and Application Commands

start and stop

The start command enables the Fiddler Everywhere system proxy and starts capturing traffic. The stop command disables the system proxy.

fiddler-cli start

Proxy enabled.

If the proxy is already in the requested state, the CLI reports Proxy is already enabled. or Proxy is already disabled.. If Fiddler Everywhere cannot change the proxy state, the command fails with the proxy_unavailable error.

status

The status command reports the sign-in, proxy, and scripting state of Fiddler Everywhere. It doesn't require a signed-in user.

fiddler-cli status

The output contains the following values (True or False):

show and hide

The show command shows and focuses the Fiddler Everywhere main window. The hide command hides it. Use show after starting Fiddler Everywhere with the --hidden option.

fiddler-cli --hidden start
fiddler-cli show

Session Commands

clear and cls

The clear command (or its alias cls) deletes the completed sessions from the Live Traffic list. Sessions that are still in progress are kept. After the command completes, Fiddler Everywhere also clears the session selection in the Live Traffic list.

fiddler-cli clear

Cleared 42 completed live session(s); active sessions were kept.

dump

The dump command exports the live sessions to a SAZ file and then clears the exported sessions. The CLI creates a uniquely named file, for example, fiddler-cli-dump-20250101-093000123-<id>.saz, so running the command repeatedly never overwrites previous exports.

• When you omit the directory, the CLI saves the file to your Desktop.
• A relative directory is resolved from the current working directory of the terminal.
• The directory must already exist. Otherwise, the command fails with the invalid_arguments error.
• Fiddler Everywhere clears the exported sessions only after the export succeeds. If the export fails, the sessions remain in the Live Traffic list.

The command prints the full path to the created file:

Live sessions exported to '/Users/<user>/Desktop/fiddler-cli-dump-20250101-093000123-....saz' and cleared.
path: /Users/<user>/Desktop/fiddler-cli-dump-20250101-093000123-....saz

If there are no live sessions, the CLI prints No live sessions to dump..

The following examples export the sessions to a specific directory:

# Windows PowerShell
fiddler-cli dump C:\captures
fiddler-cli dump "$env:USERPROFILE\My Captures"
fiddler-cli dump .\captures

:: Windows Command Prompt
fiddler-cli dump C:\captures
fiddler-cli dump "%USERPROFILE%\My Captures"
fiddler-cli dump .\captures

# macOS and Linux
fiddler-cli dump ~/captures
fiddler-cli dump "$HOME/My Captures"
fiddler-cli dump ./captures

You can open the exported SAZ files in Fiddler Everywhere. For more information, see Exporting and Importing Sessions.

Only one clear, cls, or dump command can run at a time. If you run another one while the previous command is still in progress, the CLI reports the operation_in_progress error.

Breakpoint Commands

Breakpoint commands pause matching sessions so that you can inspect and modify them in Fiddler Everywhere before they continue. For more information about breakpoints, see Breakpoints.

Each breakpoint command holds a single value. Running the command again with a new value replaces the previous one. Running the command without a value clears that breakpoint. For example:

fiddler-cli bpu example.com/api   # Break on requests to example.com/api
fiddler-cli bpu example.com/auth  # Replace the URL condition
fiddler-cli bpu                   # Clear the URL breakpoint

The text and method values that you pass to the breakpoint commands are case-sensitive. For example, fiddler-cli bpu /API/ doesn't match the /api/ URLs, and fiddler-cli bpm POST doesn't match requests that use a lowercase method value.

The g command (or its alias go) resumes all sessions that are currently paused at a breakpoint:

Resumed 3 paused session(s).

Example: Debugging an API Call

The following flow pauses the responses of failing API calls, lets you inspect them, and then cleans up:

1. Start capturing and set a response breakpoint for server errors:

   sh

   fiddler-cli start
   fiddler-cli bps 500

2. Reproduce the problem in your application. Fiddler Everywhere pauses each response with status code 500 so that you can inspect or modify it in the Live Traffic list.

3. Resume the paused sessions:

   sh

   fiddler-cli go

4. Clear the breakpoint and export the captured sessions for later analysis:

   sh

   fiddler-cli bps
   fiddler-cli dump

Temporary Rule Commands

The urlreplace and overridehost commands create temporary rules that modify the captured traffic. The temporary rules and the breakpoints that you set through the CLI behave as follows:

• They are stored in memory and are lost when you close Fiddler Everywhere.
• They apply even when the Rules switch in the Rules tab is off.
• They are evaluated before the rules defined in the Rules tab and take priority over them.
• They don't appear in, and don't change, the rules saved in the Rules tab.

urlreplace

The urlreplace <find> <replace> command replaces the find text with the replace text in the URL of each future request that contains find. The match is case-sensitive.

# Send production API calls to a staging server
fiddler-cli urlreplace api.example.com api.staging.example.com

The CLI holds a single URL replacement. Running the command with new values replaces the previous replacement. To remove the text from URLs, pass an empty string as the replacement value:

fiddler-cli urlreplace "/v2/" ""

To clear the URL replacement, run the command without values:

fiddler-cli urlreplace

overridehost

The overridehost <host> <target> command routes the requests for host to target. Both values must be a hostname, an IP address, or a host:port pair.

# Route example.com to a local development server
fiddler-cli overridehost example.com localhost:5000

Unlike urlreplace, you can add multiple host overrides—each call adds a new mapping. For HTTPS requests, Fiddler Everywhere ignores the certificate name mismatch that the redirection causes.

To clear all host overrides added through the CLI, run the command without values:

fiddler-cli overridehost

Cleared 2 Fiddler CLI host override(s).

See Also

• Fiddler CLI
• Custom CLI Commands
• Modifying Traffic with Rules
• Exporting and Importing Sessions