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Agent Not Connecting

If you've already tried the browser permissions fix and the universal fix and the agent still won't connect, this page covers less common causes.

How the Connection Works​

The Cirkit Create Agent runs a local web server on your computer, listening on ports 8991–9000. When you open Cirkit Designer in your browser, it sends requests to http://localhost:8991/info through http://localhost:9000/info to find the agent. If any port responds, the connection is established via WebSocket.

Possible Causes​

Firewall or Antivirus Blocking Localhost Connections​

Some security software (especially on school or corporate computers) blocks applications from listening on local ports or blocks the browser from connecting to localhost.

What to check:

  • Temporarily disable your firewall/antivirus and see if the agent connects
  • If it does, add an exception for the Cirkit Create Agent (ports 8991–9000 on localhost)
  • On school-managed computers, you may need to ask your IT administrator to whitelist the agent

Port Conflict​

Another application may be using ports 8991–9000, preventing the agent from starting its server.

What to check:

Windows (Command Prompt as Administrator):

netstat -ano | findstr "8991 8992 8993 8994 8995 8996 8997 8998 8999 9000"

Mac/Linux (Terminal):

lsof -i :8991-9000

If another application is using these ports, close it or reconfigure it to use a different port range.

Browser Extensions Interfering​

Some browser extensions (ad blockers, privacy extensions, or network-related extensions) can block requests to localhost.

What to try:

  1. Open Cirkit Designer in an incognito/private window (most extensions are disabled by default in incognito)
  2. If the agent connects in incognito, one of your extensions is the cause
  3. Disable extensions one at a time to identify the culprit

HTTPS Certificate Issues​

The agent uses self-signed certificates for secure localhost connections. If these certificates are corrupted or expired, the connection may fail.

What to try:

  1. Close the agent
  2. Delete the certificates directory:
    • Mac: ~/.arduino-create/
    • Windows: %APPDATA%\ArduinoCreateAgent\
  3. Look for a cert.pem and key.pem file and delete them
  4. Restart the agent — it will regenerate the certificates automatically

Getting Further Help​

If none of the above resolves your issue, reach out on the Cirkit Designer Discord with the following information:

  • Your operating system (Windows/Mac/Linux) and version
  • Your browser and version
  • Whether the agent icon appears in your system tray/menu bar
  • Any error messages you see in Cirkit Designer