FreeCircuitSim

FreeCircuitSim is a free online electronic circuit simulator that runs entirely in the browser. There is nothing to install, no account to create, and no paid tier — every feature is available to everyone.

The simulator is built on CircuitJS1, the open-source engine originally created by Paul Falstad and ported to the browser by Iain Sharp, released under the GPL v2 licence.

Features:

• Real-time simulation with animated current flow, so you can watch charge move through a circuit as it runs
• Built-in oscilloscope for viewing voltage and current waveforms
• 50+ component types including resistors, capacitors, inductors, diodes, transistors, op-amps, 555 timers, logic gates, transformers and AVR8 microcontrollers
• 360+ ready-to-run example circuits that load in a single click, organised by category — basics, filters, op-amps, digital logic, power converters and oscillators
• 24 written guides covering everything from Ohm's Law to op-amp filters, each with a live simulation embedded in the page
• 7 step-by-step guided builds with wiring diagrams, calculations and common mistakes explained
• Circuits are shareable by URL and can be saved to your browser's local storage
• An AI circuit explainer that turns a circuit description into a plain-English explanation

Who it is for:

Electronics students, hobbyists, makers and educators who want to build and test circuits without installing software or creating an account. It is commonly used as a replacement for Multisim Live, which was retired in September 2026, and as a browser-based alternative to desktop tools like LTspice and Proteus.

What it is not:

FreeCircuitSim is not a full SPICE package. It does not offer Monte Carlo analysis, detailed noise analysis, or a manufacturer parts library. For professional analog design work, a dedicated SPICE tool remains the better choice. FreeCircuitSim is built for learning and rapid experimentation.