EEsim is a circuit simulator based on ngspice and it runs inside the browser using WebAssembly technology. The input is spice based netlist, and the output is results of the analysis that you're doing in the simulations. You are able to plot and view the results directly in the browser using high-performance WebGL plotting library webgl-plot, or download the data in CSV format for further analysis. Notice that your netlist and results are processed locally and always remain inside your browser and are never uploaded to network. The focus of this implementation is rapid analysis, sharing circuits ideas and results in VLSI and chip-design communities.