Browser requirements

CircuitSim runs the simulation engine inside your browser rather than on a server. The circuit you build is solved on your own machine, which is why the browser matters more here than on a page that only displays content.

A Chromebook, a lab PC, or a student laptop is enough. Nothing is installed.

With JavaScript turned off, the page is replaced by:

JavaScript Required

CircuitSim needs JavaScript enabled to render circuits and manage user sessions.

Please enable JavaScript in your browser settings, then return to the home page.

There is a dedicated page carrying the same heading and slightly different wording:

CircuitSim depends on JavaScript for rendering circuits and managing user sessions.

If you need help enabling JavaScript, consult your browser's documentation.

Look in your browser's site settings for the entry covering JavaScript and allow it for this site. Corporate and school machines sometimes disable it by policy, in which case an administrator has to change it. Reload the page afterward.

The simulation engine downloads on first use in a page. A blocked or interrupted download shows:

Unable to run the simulation because the SPICE engine failed to load.

The simulation engine did not finish loading within 30 seconds. Check your connection, then try Run again.

Reload the page and press Run again. If it repeats on a managed network, ask whether a proxy or content filter is blocking WebAssembly files.

An engine that loads and then quits mid run reports The simulation engine stopped, with the message The local simulation engine could not continue this attempt. Its steps are to try once more, then to reduce the run duration or result resolution if it repeats. An extremely long transient can exhaust the memory the tab is allowed to use, and shortening the run is the fix.

Ad blockers and strict privacy extensions block the security check on the sign up and log in forms, producing Security verification could not load. Disable content blocking for this site or refresh the page. Allow the site in your blocker, or use a window without extensions.

An outdated browser produces the other variant: This browser cannot complete security verification. Update your browser or try another supported browser. Updating the browser clears it.

Large circuits and long transients use real processor time. Closing other heavy tabs helps, and a machine on battery saver runs noticeably slower. If a run crawls, see The simulation is taking too long.

Try the same address in a private window, then on another network. If a specific machine fails while others work, the cause is usually an extension, a filter, or a browser several versions behind. Open the chat in the bottom right corner with your browser name and version if it still fails.