Fiddler‘s AutoResponder tab allows you to return files from your local disk instead of transmitting the request to the server.

Creating AutoResponder Rules

On the AutoResponder tab, you enter a match rule and an action string, and Fiddler will undertake the action if the request URI matches the match rule.

Tips

• Rules are applied in the order that they appear. Hit the Plus key to promote a rule to earlier in the list. Hit the Minus key to demote a rule to later in the list.
• From the context menu, you can Export a .FARX file which contains a list of rules and actions.
• You can also Import a .SAZ or Import a .FARX file to create rules based on previously captured traffic.
• You can or drag-drop sessions from the Web Sessions list to replay previous responses. You can edit a rule‘s stored response by selecting the rule and hitting Enter.
• You can also drag & drop files from Windows Explorer to automatically generate AutoResponder Rules for those files.

Matching Rules

String Literals

Fiddler will match string literals (case insensitively)

* matches

• http://www.example.com/Path1/query=example
• http://www.example.com/SomethingCompletelyDifferent

EXAMPLE matches

• http://www.**example**.com/Path1/
• http://www.something.com/Path1/query=**Example**

path1/ matches

• http://www.example.com/**Path1/**query=example
• http://www.example.com/returnUrl=**Path1/**OtherPlace

query matches

• http://www.example.com/Path1/q=**Query**
• http://www.example.com/Path1/**query**=hello

NOT: rules for String Literals

Introduced in version 2.3.2.5 similar to the previous, but the rule is applied only if the string does not match

NOT:EXAMPLE matches

• http://www.test.com/Path1/query=test

NOT:path1/ matches

• http://www.example.com/Path2/query=example

NOT:query matches

• http://www.example.com/Path1/q

Exact Match

Fiddler supports an exact, case-sensitive match syntax for expressions which begin with exact

EXACT:http://www.example.com/path matches

• http://www.example.com/path

EXACT:http://www.example.com/path matches

• http://www.example.com/Path (No Match - mismatched case)

EXACT:http://www.example.com/path matches

• http://www.example.com/path/q=Query** (No Match - substring different)

Regular Expressions

Fiddler supports regular expression syntax for expressions which begin with regex. The regular expression will be used to replace the inbound URL with the string in the Actions column. Use .+ to match a sequence of one or more characters, or .* to match zero or more characters. Use ^ at the front of your regex to mean "Start of the URL" and use $ at the tail of the regex to mean "End of the URL."

regex:.+ matches

• http://www.example.com/Path1/query=example

regex:.+.jpg. matches

• http://www.example.com/Path1/query=foo.jpg&bar
• http://www.example.com/Path1/query=example.jpg

regex:.+.jpg$ matches

• http://www.example.com/Path1/query=foo.jpg&bar (No Match - improper ending)
• http://www.example.com/Path1/query=example.jpg

regex:.+.(jpg|gif|bmp)$ matches

• http://www.example.com/Path1/query=foo.bmp&bar (No Match - improper ending)
• http://www.example.com/Path1/query=example.gif
• http://www.example.com/Path1/query=example.Gif (No Match - mismatched case)
• http://www.example.com/Path1/query=example.bmp

regex:(?insx).+.(jpg|gif|bmp)$ matches

• http://www.example.com/Path1/query=foo.bmp&bar (No Match - improper ending)
• http://www.example.com/Path1/query=example.gif
• http://www.example.com/Path1/query=example.Gif
• http://www.example.com/Path1/query=example.bmp

Got a great regular expression to share? Please send it to me using the "Contact" link at the top-right side of this page! You can learn more about regular expressions here.

You can specify regular expression options (like case-sensitivity) by leading the expression with an appropriate declaration. (?insx) works well; it turns on case-insensitivity, requires explicit capture groups, enables single-line syntax, and enables comments after the #character. Learn more on MSDN.

Actions

Beyond simply returning files, the AutoResponder can also perform special actions...

filename

Return contents of filename as the response.

http://targetURL

Return the contents of the targetURL as the response

*redir:http://targetURL

Return a HTTP Redirect to the target URL. Unlike the simple URL rule, this ensures that the client knows where its request is going so proper cookies are sent, etc.

*bpu

Break on request before hitting server. Non-final action.

*bpafter

Send request to server and break on the response. Non-final action.

*delay:####

Delay sending request to the server by #### of milliseconds. Non-final action.

*header:Name=Value

Set the Request header with the given Name to the specfied value. If no header of that name exists, a new header will be created. Non-final action.

*flag:Name=Value

Set the Session Flag with the given Name to the specfied value. If no header of that name exists, a new header will be created. Non-final action.

*CORSPreflightAllow

Returns a response that indicates that CORS is allowed.

*reset

Reset the client connection immediately using a TCP/IP RST to the client.

*drop

Close the client connection immediately without sending a response.

*exit

Stop processing rules at this point.

For rules whose match action is a regular expression, you can use Regular Expression Replacement Group expressions in the Action string to copy content from the Inbound URL to the action string. Learn more...

Rules with Non-final actions will allow the request to match multiple AutoResponder rules. As soon a rule specifying a final action is reached, the matching process exits and no further rules are processed for that session.

Latency

You can optionally induce a delay (latency) before a response is returned. To enable Latency, click the Enable Latency checkbox. Right-click one or more rules and choose Set Latency to set the desired number of milliseconds. If you wish to adjust the existing latency, simply type a plus or minus before the number of milliseconds. For instance, to reduce the latency for all of the selected sessions by 5 milliseconds, enter -5 in the prompt.

AutoResponder Reference