Can I run Verilog online without installing a simulator?

Yes. CompileBytes compiles your Verilog with iverilog and simulates it with vvp on the server, so nothing has to be installed locally. Testbench output from $display and $monitor is shown in the console.

Which Verilog simulator and version are used?

Icarus Verilog 13.0, an open-source simulator, invoked with the -g2012 flag. That covers Verilog-2005 plus the SystemVerilog subset Icarus supports, such as logic, always_ff and always_comb.

Why does my simulation run until it times out?

A design with a free-running clock, such as always #5 clk = ~clk, never stops on its own. Add $finish to your initial block, for example #100 $finish;, so the simulator exits once the interesting part of the run is over.

How do I read input from stdin in Verilog?

Standard input is file descriptor 32'h8000_0000 in Verilog. Read it with $fscanf(32'h8000_0000, "%d", n) or $fgets(line, 32'h8000_0000). Whatever you type into the stdin box is supplied to the simulation.

Can I view waveforms?

The playground shows text output. $dumpfile and $dumpvars still write a VCD file inside the sandbox, but there is no waveform viewer yet, so print the signals you care about with $monitor or $display instead.

Online Verilog Compiler & Simulator

1 file

Tap Run to execute

main.v · output appears here

main.v

Press Run to execute

Output streams here as your program runs.

Verilog 13.0Readymain.vLn 1, Col 1Spaces: 4UTF-8

About the Verilog playground

Verilog is the hardware description language used to design and verify digital circuits, from a single flip-flop to a full processor. Instead of describing steps for a CPU to execute, a Verilog module describes hardware: wires, registers and the always blocks that update them on a clock edge. CompileBytes runs your code with Icarus Verilog 13.0, compiling it with iverilog and simulating it with vvp, so testbench output from $display and $monitor appears in the console instantly.

The playground accepts Verilog-2005 and the SystemVerilog subset Icarus supports with the -g2012 flag, including logic, always_ff and always_comb. Put your top-level module in main.v, add more .v files from the file explorer for separate modules, and end the simulation with $finish so the run completes. Because the simulator runs on the server, there is nothing to install: it works for learning the language, checking a testbench before synthesis, or trying a design idea in the browser.

13.0Verilog runtime

main.ventry file

projectworkspace

stdinprogram input

How it works

Write

main.v is the entry point. Add helper files from the explorer and import them into your project.

Give it input

Use the Input panel to pipe standard input to your program when it needs data.

Run

Run sends your code to a fresh hosted runtime and streams the result into the output panel.

Keep or share

Your draft stays in this browser, and Share creates a separate snapshot link.

External resources

Hello, World

module main;
    initial begin
        $display("Hello, World!");
        $finish;
    end
endmodule

A clocked counter

module main;
    reg clk = 0;
    reg [3:0] count = 0;

    always #5 clk = ~clk;
    always @(posedge clk) count <= count + 1;

    initial begin
        $monitor("t=%0t count=%0d", $time, count);
        #50 $finish;
    end
endmodule

A module and its testbench

module adder (
    input  [3:0] a,
    input  [3:0] b,
    output [4:0] sum
);
    assign sum = a + b;
endmodule

module main;
    reg [3:0] a, b;
    wire [4:0] sum;
    adder dut (
        .a  (a),
        .b  (b),
        .sum(sum)
    );

    initial begin
        a = 4'd7;
        b = 4'd9;
        #1 $display("%0d + %0d = %0d", a, b, sum);
        a = 4'd15;
        b = 4'd1;
        #1 $display("%0d + %0d = %0d", a, b, sum);
        $finish;
    end
endmodule

Number formats and bit operations

module main;
    reg [7:0] x = 8'b1010_1100;
    initial begin
        $display("bin=%b hex=%h dec=%0d", x, x, x);
        $display("shift left: %b", x << 2);
        $display("inverted:   %b", ~x);
        $display("and mask:   %b", x & 8'h0F);
        $finish;
    end
endmodule

A for loop

module main;
    integer i;
    initial begin
        for (i = 1; i <= 5; i = i + 1) $display("%0d squared is %0d", i, i * i);
        $finish;
    end
endmodule

Case statement (a tiny ALU)

module main;
    reg [1:0] op;
    reg [7:0] a = 12, b = 5, r;
    integer k;
    initial begin
        for (k = 0; k < 4; k = k + 1) begin
            op = k[1:0];
            case (op)
                2'b00:   r = a + b;
                2'b01:   r = a - b;
                2'b10:   r = a & b;
                default: r = a | b;
            endcase
            $display("op=%b result=%0d", op, r);
        end
        $finish;
    end
endmodule

Functions and tasks

module main;
    function [7:0] double(input [7:0] n);
        double = n * 2;
    endfunction

    task show(input [7:0] n);
        $display("value %0d, doubled %0d", n, double(n));
    endtask

    initial begin
        show(21);
        show(100);
        $finish;
    end
endmodule

Reading input

module main;
    integer stdin, n, ok;
    initial begin
        stdin = 32'h8000_0000;
        ok = $fscanf(stdin, "%d", n);
        $display("Doubled: %0d", n * 2);
        $finish;
    end
endmodule

Editor guide

The editor uses Monaco, the engine behind VS Code, with language-aware editing tools and familiar keyboard controls.

Getting started

Type or paste your code into the editor, then click Run (or press Ctrl/Cmd + Enter) to execute it.

Output streams into the console panel, including runtime errors, exit status, and execution time.

Nothing to install and no account to create — code runs in an isolated hosted runtime.

A full-featured code editor

Language-aware autocomplete and IntelliSense suggestions where the editor has a matching language service

Syntax highlighting, with native compiler and runtime errors shown in the console

Bracket matching, auto-indentation, code folding, and a minimap

Multi-cursor editing plus find & replace (Ctrl/Cmd + F)

Full undo/redo history and copy to clipboard

Built on Monaco — the same editor that powers VS Code

Running & testing your code

Run on demand with Run or Ctrl/Cmd + Enter, or turn on Auto-run in the editor settings to execute after each typing pause

Stop long-running or infinite programs at any time

A real console shows standard output, errors, exit status, and execution time

Program input

Pass standard input (stdin) to your program from the Input panel — one value per line

Make it yours

Switch between light and dark themes

Adjust font size and other editor settings

Toggle side-by-side or top/bottom layouts

Enter distraction-free fullscreen mode

Share & save

Generate a shareable link to your exact code in one click — no login needed

Your work autosaves to your browser, so you can pick up where you left off

Copy the active file to your clipboard

Handy keyboard shortcuts

Run code: Ctrl/Cmd + Enter

Find & replace: Ctrl/Cmd + F

Open the full shortcut list from the keyboard icon in the toolbar

Verilog project files

Verilog is one of 24 linked-project compilers. Run always starts main.v; selecting a helper tab changes what you edit, not the entry file.

All source tabs are submitted together so main.v can use sibling files.

Linked-project languages (24): Node.js, TypeScript, Deno, Python, C, Go, Dart, Swift, Rust, Ruby, PHP, Java, Kotlin, C++, C#, Nim, Crystal, Haxe, Zig, Scala, D, Verilog, Bun, Objective-C.

Single-file scratchpads (46): Matplotlib, NumPy, pandas, Haskell, Clojure, Perl, Lua, Tcl, jq, Raku, Elixir, Bash, Zsh, Nushell, R, Assembly (NASM), Julia, Octave, Groovy, PowerShell, Visual Basic .NET, Odin, Pascal, Lisp, Erlang, CoffeeScript, COBOL, BASIC, V, Racket, OCaml, Prolog, AWK, Emacs Lisp, Emojicode, Forth, F#, Fortran, Assembly (NASM64), Solidity, Mojo, Ada, WASM (WAT), Gleam, Shell Script (sh), Scheme. Their extra project files are not submitted to the runtime.

Download

Download project exports every Verilog tab and a README in one ZIP archive.

Every shortcut, searchable:

Verilog

Verilog Playground

Write

Give it input

Run

Keep or share

Run

Editing

Navigation

Selection

Terminal