Articles on: Troubleshooting

WebSocket, firewall, or Cloudflare blocking SimplyPrint (live data, Cloud Slicer)

WebSocket, firewall, or Cloudflare blocking SimplyPrint (live data, Cloud Slicer)


Symptoms this article covers: the panel loads but live printer status never appears, the "Connecting…" banner stays forever, the Cloud Slicer hangs without finishing, file uploads fail, you're on a school / office / enterprise network, or multiple websites are slow at the same time.


These are network problems, not browser problems. The browser is fine - the connection between you and SimplyPrint (or one of its dependencies) is the bottleneck.


What SimplyPrint needs to reach

At minimum, your network has to allow:



The complete list (with ports and reasoning for your IT department) lives at simplyprint.io/hardware-network-requirements. Send that link to your network admin.


30-second test: try mobile data

Turn your phone's mobile hotspot on, connect your computer to it, reload SimplyPrint.


  • Works on hotspot, fails on your normal network: the cause is your network or its firewall.
  • Fails on both: not a network problem.


"Connecting…" forever (WebSocket blocked)

The panel loads but live printer data never appears. The banner at the bottom keeps saying "Connecting…". Almost always: WSS to ws.simplyprint.io is blocked. Common on enterprise and school networks. Ask IT to allow WebSocket traffic to *.simplyprint.io.


See How SimplyPrint sends prints / Gcode to the printer for the WebSocket architecture context.


Cloud Slicer hangs (SSE blocked)

You start a slice and the progress bar stalls. The Cloud Slicer uses SSE over slicing.simplyprint.io, which some restrictive firewalls block as an "unknown protocol". Same fix: allow SSE to *.simplyprint.io.


Browsers time out long requests by themselves, regardless of our generous server-side timeouts.


  • Satellite (Starlink, Viasat): high latency causes intermittent failures
  • Heavily-shared Wi-Fi (dorms, cafes, conferences)
  • VPNs in distant regions (200+ ms added round-trip)


If the panel detects you're on a slow or metered connection, your debug report will show it under network.effectiveType. Hard-wired Ethernet usually helps more than tweaking the browser.


Cloudflare / ISP routing problems

SimplyPrint sits behind Cloudflare, like a large chunk of the internet. A few times a year, certain ISPs in certain regions get re-routed badly through Cloudflare's network and a lot of sites misbehave at once. A well-documented recent example: Deutsche Telekom users in Germany were re-routed through suboptimal Cloudflare paths.


If many of your sites are slow at the same time, check:



Workaround: switch to mobile data (different network path).


Printer-side connectivity

If the panel works fine but a specific printer says "offline", the printer's own network connection is the issue, not yours. See:



Edge case: DevTools "Block request URL"

If you've been debugging in DevTools yourself: the Network tab has a "Block request URL" feature. It's persistent and easy to forget. Close DevTools, reopen, check the blocking list, clear anything leftover.



Updated on: 26/05/2026

Was this article helpful?

Share your feedback

Cancel

Thank you!