Match & Replace

The Match & Replace feature allows you to define match & replace rules. These rules can be used to modify requests as they pass through the proxy.

Match & Replace rules can be organized into collections, which allows you to group rules however you see fit. For example, you can create a collection to group User-Agent rules, header rules, etc.

Match & Replace

To create a Match & Replace rule, click on the + icon of the collection where you want to create the rule or New Rule to create it in the Default collection.

When creating a new rule, you can update the following fields:

  • Name: A name for the rule.
  • Strategy: Defines what part of the request to perform the match/replace on, such as request header, response header, request body, request first line, etc.
  • Search as regex: If the Search term is a regex or a simple string match
  • Search term: The term to search for in the defined part of the request or response.
  • Replace term: The term to replace the search term with.

Testing your rule

When you're done updating your rule, you can use the bottom panes to test your rule against a mock request/response.

Click on the Test button and see if your rule works as intended.

Active rules

You can enable or disable individual rules by clicking on the checkbox next to each rule in the tree view.

Enabled rules will be shown in the Active rules section of the page. This section displays the list of the rules that are currently active and will be applied to the requests that pass through the proxy.


The order of the rules in the "Active rules" section determines the order in which they will be applied to the requests and responses.

You can change the order of the rules by dragging and dropping. This allows you to adjust the order to suit your needs, and can be useful when working with multiple rules that may have conflicting or overlapping conditions.


Append a request header with a custom string

Many popular bug bounty programs require a custom header to be sent with your requests. You can do this in Caido using the Match and Replace feature. An example of this for Bugcrowd is to send the word bugcrowd as your User-Agent header.


Request header (Enable Search as Regex)


^(User-Agent: .+)


$1 bugcrowd