Knowledge Base > Licensing > Network requirements for licensing

Network requirements for licensing

Diffblue Cover needs an active internet connection to authorize its use *. It needs to connect to both a Diffblue server and a LicenseSpring server; these servers are accessed on port 443:


To identify individual devices we transfer data about hardware components over this connection. Further details are available in the Privacy Notice.

* (Unless you are using Diffblue Cover Enterprise Edition, in which case please see these separate instructions.)


  1. Check you have an active internet connection at all times when using Diffblue Cover.
  2. Ensure you can access via a web browser; you will automatically receive a confirmation message when this is successful.
  3. Ensure you can access via a web browser, you should see the message “Welcome to the LicenseSpring API”.
  4. Ensure that any Proxy Server settings are correctly setup (see the bottom of this page).
  5. Please speak to your network manager about whitelisting the URLs above, and checking that port 443 is open.
  6. For the Diffblue Cover IntelliJ Plugin, restart IntelliJ.
  7. Try temporarily disabling anti-virus, malware detector or any firewall software.
  8. A detailed logfile is available which shows further diagnostic information about the license check process - please review the logs:

For further help troubleshooting licensing network connection issues, please contact Diffblue Support.

Using a Proxy Server

Diffblue Cover IntelliJ Plugin

Please ensure you have the Proxy Server details configured in the IntelliJ settings page and then restart IntelliJ:

  • Windows and Linux: File | Settings | Appearance and Behavior | System Settings | HTTP Proxy
  • macOS: IntelliJ IDEA | Preferences | Appearance and Behavior | System Settings | HTTP Proxy

Please also see the HTTPS certificate errors information below.

Diffblue Cover CLI

Diffblue Cover CLI utilizes the system Java proxy configurations; these can be set via the environment variable JVM_ARGS which details the proxy server FQDN and port, for example:

JVM_ARGS=" -Dhttps.proxyPort=8080"

As shown in this example:

HTTPS certificate errors

If you have a proxy server that rewrites HTTPS connections and packages them with its own certificate, you may get an L018 output code. The simplest way to fix this is to disable certificate checks. You can do this by setting either the java system property dcover.disable.ssl.license.cert.check or the environment variable DCOVER_DISABLE_SSL_LICENSE_CERT_CHECK to true. In IntelliJ you can add system properties using Help -> Edit custom properties.... This will open a file to which you should add a line such as:


If you are using the CLI, it is usually easier to set the environment variable, for example:


To avoid typing this every time you use the product, you should set this variable in your user profile or startup scripts. For help, please contact Diffblue Support.

Offline Mode and Offline License Activation

Users of the Diffblue Cover Enterprise Edition are not required to maintain an active internet connection. In addition Enterprise users can use the Cover CLI command dcover activate --offline to activate a license while offline. For more details follow the articles here: