HTTP Toolkit for Performance Engineers

In this blog post, we are going to deep-dive into the HTTP Toolkit and its features. As a performance engineer, it is our responsibility to learn various tools and technologies. Based on the issue, you need to leverage the right tool to fix the problems, just like plumbers. Let us see HTTP Toolkit for Performance Engineers.

What is HTTP Toolkit?

It is an open-source tool to debug, test, intercept HTTP(S) requests. It can intercept: desktop browsers such as Chrome, Firefox, Edge etc., Android apps, Python, Java, Ruby, and all terminal-based apps, and Electron apps.

If you are interested to learn about MITM, you can check my below YouTube series.

MITM YouTube Playlist

How to install HTTP Toolkit?

HTTP Toolkit works on Windows, Mac and Linux. Head to website and download the relevant package to install it.

Download - HTTP Toolkit for Performance Engineers
Download – HTTP Toolkit for Performance Engineers

After successful installation, you can launch HTTP Toolkit. Below is the user interface of HTTP Toolkit.

HTTP Toolkit Interface

First Interception using HTTP Toolkit

Let us intercept HTTP traffic in the HTTP Toolkit. In this example, let us use the Firefox browser to intercept traffic. HTTP Toolkit intercepts HTTP and HTTPS traffic. The HTTP Toolkit acts as a proxy between the client and server and captures the traffic. Once the requests have been captured, you can view, modify, and deep-dive into it.

  • Launch HTTP Toolkit
  • Click on Intercept
  • Click on Firefox as shown below.
Intercept Traffic
Intercept Traffic

This will launch Firefox and open automatically as shown below. If you are getting below message, then the HTTP Toolkit is working fine.

Testing the proxy
Testing the proxy

Now, it is time to record our business actions in the browser. For demonstration purpose, let us use web app.

Once the app is launched, perform the below transactions.

  • Login
  • Send $10 to Alice
  • Deposit $10 to External Account
  • Sign out

Once the recording is done, you can close the Firefox window.

Congratulations! You have intercepted the traffic on HTTP Toolkit.

Viewing the intercepted traffic

To view the intercepted traffic, go back to HTTP Toolkit, click on View. In right side, you can see the list of HTTP requests in a table format.

View HTTP Requests
View HTTP Requests

To view more details about the HTTP request, click on the row. On the right side, you can view the selected request, response, and body as shown below.

View HTTP Request and Response
View HTTP Request and Response

Features such as performance and cURL are paid.

Filter the traffic

As you aware, HTTP Toolkit captures all the traffic between the client and server. We need to remove the noises from the captured traffic. HTTP Toolkit comes with filtering.

At the bottom, you can filter out using various tags such as status code, method, hostname, headers and more.

e.g. if we want to filter only bank of anthos traffic, we could enter the following filter.


It supports multiple filters as well.

Rewriting the intercepted traffic

HTTP Toolkit supports rewriting the HTTP requests, responses and mocking. This will help us to test various parameters for debugging purpose.

To demonstrate the rewrite, let us redirect from to

If you are launching a bank of anthos app, it will throw the response of

As we are using the free version, we are kind of limited in terms of rewrite options.

First, we need to create a rule by going to Mock tab.

Click on Add a new rule to rewrite requests and responses.

Create a rule

Configure the below rule and hit Save button.

Save a rule

The above rule pauses the interception if the URL is We need to edit the request/response manually to resume.

Go to Intercept and launch the Firefox browser.

Then, open app.

The browser will not open bank of anthos website. If you go to HTTP Toolkit, it will prompt you to take the action as shown below.

Pause the capture
Pause the capture

To rewrite the response, edit the URL to and then click on Resume.


Now, if you switch back to Firefox browser, you can see the response, instead of bank of anthos response.

Rewrite response
Rewrite response

Also, in the HTTP Toolkit response body as well, you can see the response.

Validate the response

Congratulations! You have learned how to capture, intercept, and modify the request/response using HTTP Toolkit.


The HTTP Toolkit is a great utility for debugging, test, intercepting traffic. It has a simple user interface, easy to learn and supports various technologies and platforms. If you want to become a power user, you need to subscribe to the pro features. Alternatively, you can use MITMProxy, which can be ideal for your use.

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