Modify API Response

Navigate to the HTTP Rules section in the Requestly app. Select Add Rule and choose the Modify API Response option. Give it a meaningful name and description.

Choose the resource type for modification:

• REST API: Modify XHR/Fetch requests initiated by web pages.

• GraphQL: Target and modify GraphQL APIs by operation.

• HTML/JS/CSS (Desktop App Only): Modify static files for desktop applications.

Specify the criteria for matching API responses. Define the URL pattern or use response attributes such as status code to identify the target response. Use Source Conditions like:

• URL, Host, or Path with Regex, Contains, Wildcard, or Equals

• Filters for specific webpages, request types, methods, or payloads

If targeting GraphQL APIs, filter queries by their operation name. Add the Payload JSON Key (e.g., operationName) and specify the corresponding Value (e.g., getUsers) to target specific GraphQL operations.

Modify the status code of the response using the dropdown menu. Choose from:

• 2XX for successful responses

• 4XX for client errors

• 5XX for server errors

If left empty, the original status code remains unchanged.

Choose one of the following methods to modify the response data:

• Static Response Modification: Input a static value as the response body.

• Programmatic Modification Script (JavaScript): Use JavaScript to dynamically modify responses. The script provides access to parameters like:

  • method: HTTP Method (GET, POST, etc.)

  • url: Full URL of the request

  • response: Original response body (string)

  • responseType: Content type of the original response

  • requestHeaders: Headers sent with the request

  • responseJSON: Original response parsed as a JSON object

  Example:

  Copyfunction modifyResponse({ responseJSON }) {
      responseJSON.modifiedKey = "modifiedValue";
      return responseJSON;
  }
  

  

  You can tick the “Server this response body without making call to the server” checkbox as the label suggests it will ensure you get the response locally without hitting your API server.

Click Save to store the rule and toggle it ON. This will apply the rule to the defined source conditions.

To ensure the rule is working correctly, click the Test button and enter the URL of the page where you want to apply this rule. This will open the webpage in a new tab, with a widget showing the status of applied rules and logs any debugging information in the SessionBook.