Example using Cypress to test Create-React-App site running with custom certificate for domain “my-secure-site”

Read the blog post Cypress Hosts Option

Making certificate

Before testing the site, we need to make local self-signed certificate in the folder “.cert”. On Mac I used the following commands to create a self-signed certificate for domain “my-secure-site”

$ brew install mkcert
$ mkcert -install
$ mkdir .cert
$ mkcert -key-file ./.cert/key.pem -cert-file ./.cert/cert.pem "my-secure-site"

You should now have two text files in the folder .cert: cert.pem and key.pem

Start the local site

Let’s use the `react-scripts to start the site with the .env.development settings (HTTPS, local certificate)

$ npm start

If you open the browser at https://localhost:3000 you will see an error.


The certificate we just made is for domain “my-secure-site”, not for “localhost”. If we click “Proceed” then the browser shows the SSL error while accessing the site.


Hosts file

We created the SSL certificate for domain “my-secure-site”, yet are trying to access “localhost”. We cannot just go to “https://my-secure-site” because the browser does not know that domain “my-secure-site” should map back to our local computer address The DNS system has no record for “my-secure-site”. Instead we need to set in our local networking settings a DNS “helper”, telling the local computer that “my-secure-site” name is at IP address. We can do it via hosts file. On Mac I could edit the /etc/hosts file to add my own record my-secure-site

Then in the browser I can go to https://my-secure-site and see my local React application without any browser errors.


I can avoid messing with the hosts file on the computer and instead specify the local DNS names directly on the cypress.json file. For example, to work with the local HTTPS site:

  "baseUrl": "https://my-secure-site:3000",
  "hosts": {
    "my-secure-site": ""

Note that the “hosts” record only specifies the domain -> IP mapping, the port number is unchanged. With the above cypress.json I can visit the base URL in Cypress without any changes to /etc/hosts file on the machine.


Small print

Author: Gleb Bahmutov <[email protected]> © 2021