How to test an API running on localhost from outside localhost?

4 min readSep 17, 2017

In this blog post we will teach you how to test an API running on localhost from outside localhost. This is useful if you are in the process of developing an API and want to interact with it from Apibot.

Before we get started you will need two things:

Ngrok (download free)
A working REST API running on localhost

What is ngrok?

Ngrok is a free command line tool that allows you to expose a service running on your local machine to the internet. Make sure you download and put ngrok somewhere in your path e.g. /usr/local/bin/ngrok.

Run your web service

For the purpose of this example I will be running a simple Rails app that I found somewhere in the internet. If you want to follow along with this tutorial but don’t know what to run, you can run something simple like an HTTP echo server.

Application in development on http://0.0.0.0:**3000**

After having installed ngrok, run the following command to expose your server to the internet:

ngrok http <port number>

Replace <port number> with the port number where your server is running. After running the ngrok command you will notice that your terminal screen looks something like this:

Tunnel Status                 online
Update                        update available (version 2.2.8, Ctrl-U to update)
Version                       2.0.25/2.1.18
Region                        United States (us)
Web Interface                 http://127.0.0.1:4040
Forwarding                    http://8ddae8ce.ngrok.io -> localhost:3000
Forwarding                    https://8ddae8ce.ngrok.io -> localhost:3000

Take note of the https://*.ngrok.io URL. Whenever you make an HTTP request to this URL it will be redirected to your localhost.

The ngrok UI

You will also notice that ngrok is displaying another URL

Web Interface                 http://127.0.0.1:4040

Open that link on your browser. This is a realtime mini-dashboard that displays useful information about your ngrok connection as well as a history of HTTP requests sent to ngrok.

Now that we have everything setup, let’s start testing our API.

Testing the API

Now that we have an API running and exposed via ngrok to the web, we can use Apibot to test some of its endpoints. For the purpose of this blog post we will create a simple graph which sends an HTTP request to authenticate with the API.

Step #1: Creating a graph

Start Apibot, authenticate and then click on the ‘create a new graph’ button. This will create an empty graph. Graphs in Apibot are analogous to “tests” or “workflows”.

Step #2: The Config

We now need to create a config node. The config node makes it possible to define variables which can later be accessed from other nodes.

Add a config node to the graph and enter the following property:

key: root, value: https://<subdomain>.ngrok.io

Make sure you replace <subdomain> with your ngrok subdomain.

Step #3: The HTTP request

Add an HTTP request and fill in the required arguments. This will of course depend on the API you are communicating with.

The most important thing to notice here is that in the url field I entered ${root}/login. When a graph is executed, ${root} will be replaced with whatever you defined the root variable to be, which in our case is the ngrok URL.

Step #4: Running the graph

Click the run button. This will send the HTTP request to the ngrok URL. If you open the ngrok UI (normally running on http://127.0.0.1:4040) you will see your request.