How to Modify Response Status Code in Charles Proxy

Kanishk Rawat

September 23, 2024

5MIN READ

Learn to modify response status code in Charles Proxy and see why Requestly provides a simpler, more efficient solution for managing HTTP requests and responses

Introduction

During local development you might want to override http status code for various reasons like simulating error codes for testingetc.

“Rewrite Response Status” comes handy in such cases where you want to overwrite HTTP status from request and responses without making any changes to your codebase.

Rewrite Response Status tool can also be used to

Mocking Server Downtime or Maintenance
Simulating Unauthorized Access

Setting up Rewrite Response Status in Charles Proxy is little complex. You can follow the steps below to configure Rewrite Response Status tool with ease.

A Browser Extension, that just needs you to fill 2 fields and doesn’t have VPN issues, is also explained later in this post. You can also use that in place of Charles Proxy.

How to Configure Charles Proxy’s Rewrite Tool to Modify Response Status code

Open Charles Proxy and make sure the proxy is turned on and capturing traffic.
Go to the top menu and click on Tools.
In the dropdown, choose Rewrite.

This will open the rewrite settings window Here check Enable rewrite box and click Add.

Rename the rule to your liking and add a location to which the rule should be applied to

Protocol: Here you can select your site’s protocol http or https.
Host: Here you can enter the host/domain that you want to apply the rule to.
Port: You can specify the port on which your site is running.
Path: Define the path if you want the rule to apply only to specific paths on the host.
Query: Here you can define the query parameters that should be targeted.

Now Save the location and click on add in the actions section

Type: The type tells Charles what to modify. Here we have to select the type of rule we want to use Response Staus.
Where : Decide whether to apply the change on the request the response, or both. Since we want to allow CORS we will modify only the response.
Match: You need to tell Charles when to apply the rule. This is done by matching specific text in the request URL or we can select Match whole value.
Replace: Once a match is found, Charles replaces the text you’ve specified. For example, in this case, we want to replace the status code to 404.

After saving this you should be able to see the rule and its modifications.

Now visit the site you selected and you can check in the network tab that the status codes of requests are changed to 404.

I hope you are able to configure Rewrite Response status tool, if you are facing issues in setup of SSL read about SSL setup on Charles Proxy official documentation.

Due to this complicated setup process of Charles Proxy and issues with VPN we, at Requestly, came up with a smart solution. We developed a Browser Extension that can sit inside the browser and use browser’s APIs to intercept and modify your network requests and responses.

Modify API Response rule in Requestly

Requestly is designed differently so it doesn’t need any SSL configuration and hence works seamlessly with your VPNs. Rewrite Response status is simplified as “Modify Response” in Requestly. With just 2 inputs i.e. source URL matching condition, Header value.

There are more advanced rules in Requestly & other features to help you test the working of the rule along with details of how to use this rule are explained below.

Overview of Configuration Options

Options: Here, you can choose between static data or dynamic (JavaScript) data for modifying the response body.
Status Code: This setting allows you to define the status code that should be returned when specific conditions are met.
Source Condition: This condition enables filtering or modifying requests based on their source. In the example, the source is set to a URL containing google.com, meaning only requests containing this URL will be affected.
Filter out Condition: This enables further filtering by defining exceptions or specific rules that exclude certain requests. This makes sure only targeted requests are affected, ignoring the ones that don’t match the conditions.

Steps to Configure Requestly’s Modify Response rule to modify response status code

Install Requestly Extension: Download and install Requestly’s browser extension.
Open Requestly Dashboard: Visit app.requestly.io and log in.
Click on the Rules tab and then New Rule .
Select Modify API Response as the rule type.
Specify the URL or URL pattern in the Source Condition.
In the Modify API Response section, enter 404 in the Response Status Code field
Name your rule and click Save.

After saving the rule, you can test it. If you’d rather not set it up manually, we’ve created a shared rule for modifying response Body. You can import it by clicking the button below.

Or create your own Rule by following the guide below

The app requires the Requestly Chrome extension to function properly. If you don't have it installed, you'll be prompted to install the extension

Interactive Guide

Check out this interactive and easy explanation of how to create this rule

Migrate from Charles proxy

If you already have a Charles Proxy setup and want to give Requestly a try, You can import these tool settings in Requestly in just few clicks

Requestly currently supports following tools that you can import from Charles Proxy:

Rewrite
Map Local
Map Remote
No Caching
Block lists
Block Cookies

Steps to import

In Charles Proxy, go to the top menu bar and select Tools > Import/Export Settings.

In the popup window that appears, switch to the Export tab. Under the Tools section, select the tools you want to export and click the Export button at the bottom right.

Open the Requestly dashboard. If you don’t have any existing rules, you’ll see an Import settings from Charles Proxy .

You can also open it from https://app.requestly.io/import-settings-from-charles

Upload or drag your exported Charles .xml file into Requestly.

Once the import is successful, your Charles Proxy settings will be converted into Requestly rules.

Conclusion

I hope you have got a clear understanding of both the Rewrite Response Status tool in Charles Proxy and how Requestly can achieve the same results with greater ease. While Charles Proxy effectively handles the task, Requestly offers a modern, simple and efficient experience.

Since Requestly operates directly from your browser and leverages built-in browser APIs, there’s no need for complex SSL configurations, eliminating the VPN issues often encountered with Charles Proxy. Plus, you don’t need to switch between different tools — everything you need is right in your browser.

Love for Requestly is reflected in its 4.4 ⭐ rating from over 1,200 users on the Chrome Web Store. Requestly is being used by 200K+ developers across the world.

Happy Debugging!!!

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Kanishk Rawat

Kanishk Rawat, a tech enthusiast since childhood, has mastered programming through dedication. Whether solo or in a team, he thrives on challenges, crafting innovative solutions .