Circuit JS vs CircuitLab

CircuitLab and Circuit.js (also known as Falstad Circuit Simulator) both enable electronic circuit simulation in a web browser, but they serve different audiences with different priorities regarding features, cost, and simulation depth.

Circuit.js is a free, open-source circuit simulator originally created by Paul Falstad and now maintained as a community project. Its defining characteristic is the animated visualization of current flow, voltage levels, and signal propagation through circuits. Components light up with color-coded indicators showing instantaneous voltage and current, making it extraordinarily intuitive for understanding how circuits behave. You can literally see electrons flowing through wires, capacitors charging, and signals propagating through logic gates.

CircuitLab is a commercial web-based circuit simulator designed for professional and educational use. It provides a clean schematic editor with a comprehensive component library, SPICE-based simulation engine, and features like DC sweep, AC frequency analysis, transient simulation, and parameter stepping. The interface resembles professional EDA tools like LTspice but runs entirely in the browser with no installation required.

The simulation engines differ in capability. CircuitLab uses a SPICE-derived engine that handles complex analog circuits, operational amplifiers, transistor-level designs, and mixed-signal circuits with professional accuracy. Circuit.js uses a simpler simulation approach that works well for basic analog and digital circuits but may not accurately model complex semiconductor behavior, feedback loops, or high-frequency effects.

For education, Circuit.js is exceptional. The animated current flow visualization makes abstract electrical concepts tangible. Students can build a circuit, adjust component values with sliders, and immediately see how current distribution changes. This real-time visual feedback accelerates learning in ways that numerical simulation output cannot match. Many university courses use Circuit.js specifically for this pedagogical advantage.

CircuitLab targets a broader audience including professional engineers, advanced students, and educators who need accurate simulation results. Its component library includes realistic models for specific transistors, op-amps, and ICs rather than idealized generic components. When you need to verify that a design will work with actual parts before building a prototype, CircuitLab's accuracy matters.

The schematic editor in CircuitLab is more capable for complex designs. It supports hierarchical schematics, subcircuits, custom component creation, and proper schematic annotation. Circuit.js uses a simpler point-and-click interface that works well for small circuits but becomes unwieldy for designs with more than twenty or thirty components.

Collaboration features exist in CircuitLab but not in Circuit.js. CircuitLab allows sharing circuits via links, embedding interactive simulations in web pages, and collaborative editing for team projects. Circuit.js circuits can be shared via URL encoding (the circuit state is encoded in the URL), but there is no real-time collaboration or team features.

Pricing reflects the different models. Circuit.js is completely free with no limitations. CircuitLab offers a free tier with limited saves and a paid subscription (around $10/month for individuals, with educational and team pricing available). For hobbyists and students on a budget, Circuit.js provides unlimited use at no cost.

The component libraries differ in scope. CircuitLab includes hundreds of components with manufacturer-specific models. Circuit.js has a smaller but well-curated library covering common passive components, semiconductors, logic gates, and basic ICs. For most educational and hobbyist circuits, Circuit.js has everything needed. For professional designs requiring specific component models, CircuitLab is necessary.

Export and documentation capabilities favor CircuitLab. It can export publication-quality schematics, generate netlists, and produce simulation reports. Circuit.js can export circuit images and share URLs but lacks formal documentation generation features.

Feature	Circuit JS	CircuitLab
Sugggest Score	—	—
Category	Development	Development
Pricing	Free	Freemium

Product Overview

Circuit JS

Description: Circuit JS is an easy-to-use, interactive circuit simulator and schematic capture tool for the web. It allows users to easily create and simulate circuits using standard components without installing any software.

CircuitLab

Description: CircuitLab is an easy-to-use, online circuit simulator and schematic capture tool. It allows users to easily create, analyze and share circuit designs with drag-and-drop interface and simulated interactive testing.

Key Features Comparison

Circuit JS Features

• Interactive circuit simulator
• Schematic capture tool
• Standard components
• Runs in web browser
• Collaborative editing

CircuitLab Features

• Online circuit simulator
• Drag and drop interface
• Interactive circuit testing
• Circuit sharing and collaboration
• SPICE simulation engine
• Large component library
• Waveform visualization
• Schematic capture
• Version control

Pros & Cons Analysis

Circuit JS

Pros

• Easy to use interface
• No installation required
• Real-time circuit simulation
• Component library
• Shareable circuits

Cons

• Limited component library
• No offline usage
• Collaborative editing can be chaotic

CircuitLab

Pros

• Easy to use interface
• No software installation required
• Real-time circuit simulation
• Component library includes common components
• Can simulate analog and digital circuits
• Waveform analysis tools
• Collaboration features
• Free tier available

Cons

• Limited component library in free tier
• Simulation speed can be slow for large circuits
• No offline access
• No native mobile app
• Lacks some advanced simulation features

Pricing Comparison

Circuit JS

• Free

CircuitLab

• Freemium