Verilog Online Compiler | Free Online Compiler

Code

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

STDIN (optional)

Args (space separated)

Output

What Is the Verilog Online Compiler?

This tool lets you compile and simulate Verilog HDL (Hardware Description Language) code directly in your browser without installing any EDA tools. Whether you are learning digital design concepts or quickly testing a module, this compiler provides instant simulation results.

Verilog is one of the most widely used hardware description languages for designing and verifying digital circuits, from simple logic gates to complex processors and FPGA designs. This online environment uses Icarus Verilog, an open-source Verilog simulation and synthesis tool, to compile and simulate your designs.

All code executes on a remote sandboxed server powered by the Piston API. Your browser sends the Verilog source to the server, which compiles it with Icarus Verilog, runs the simulation, and returns the text output including any $display or $monitor messages.

How It Works

Write your Verilog code in the editor panel. The editor starts with a simple module that prints a message using $display. You can replace it with any valid Verilog design and testbench.
Include a testbench in the same file to drive your design. Use initial blocks with $display statements to observe signal values during simulation.
Click the Run button to send your code to the Piston execution server. The server compiles your Verilog source with Icarus Verilog and runs the simulation.
View the results in the Output panel. You will see all text output from system tasks like $display, $monitor, and $write, along with any compilation errors or warnings.

Step-by-Step Example

Suppose you want to design a simple 2-to-1 multiplexer and verify it with a testbench. Here is how you would do it:

First, type the following code into the editor panel:

module mux2to1(input a, input b, input sel, output y);
    assign y = sel ? b : a;
endmodule

module tb_mux;
    reg a, b, sel;
    wire y;

    mux2to1 uut(.a(a), .b(b), .sel(sel), .y(y));

    initial begin
        $monitor("a=%b b=%b sel=%b | y=%b", a, b, sel, y);
        a = 0; b = 0; sel = 0; #10;
        a = 1; b = 0; sel = 0; #10;
        a = 0; b = 1; sel = 1; #10;
        a = 1; b = 1; sel = 1; #10;
        $finish;
    end
endmodule

Click the Run button. The compiler builds your design and runs the simulation. The Output panel displays the monitored signal values at each time step:

a=0 b=0 sel=0 | y=0
a=1 b=0 sel=0 | y=1
a=0 b=1 sel=1 | y=1
a=1 b=1 sel=1 | y=1

You can verify that when sel=0 the output follows input a, and when sel=1 the output follows input b.

Use Cases

Learning digital design fundamentals. Experiment with combinational logic, sequential circuits, flip-flops, counters, and state machines in a zero-setup environment.
Writing and testing testbenches. Create testbenches with stimulus generation and output verification to validate your designs before moving to an FPGA or ASIC flow.
Practicing for coursework and exams. Students can quickly prototype and test Verilog assignments without needing access to commercial EDA tools.
Prototyping small modules. Test individual modules like ALUs, decoders, encoders, and memory controllers before integrating them into larger designs.
Exploring Verilog syntax. Quickly verify how specific Verilog constructs behave, such as blocking vs non-blocking assignments, generate statements, or parameter usage.

Limitations and Notes

Simulation only. This environment simulates your Verilog code but does not perform synthesis, place-and-route, or generate bitstreams for FPGA programming.
Single file execution. All modules and testbenches must be defined in a single file. Multi-file projects and include directives are not supported.
Limited SystemVerilog support. Icarus Verilog supports some SystemVerilog features, but the full SystemVerilog specification is not available.
No waveform viewer. While $dumpfile and $dumpvars compile, there is no integrated waveform viewer. Use $display and $monitor for text-based output.
No vendor-specific libraries. Xilinx, Intel/Altera, and other vendor-specific primitives and IP cores are not available.
Execution timeout applies. Simulations that run too long are terminated automatically. Make sure to include $finish in your testbench.

Frequently Asked Questions

What Verilog version does this compiler use?

It uses Icarus Verilog provided by the Piston execution engine.

Does this support SystemVerilog?

SystemVerilog support is limited. Icarus Verilog supports some SystemVerilog features but not the full specification.

Can I write testbenches?

Yes, you can write testbenches with initial blocks, $display, $monitor, and $finish to verify your designs.

Does this support synthesis?

No, this is a simulation-only environment. It compiles and simulates your Verilog code but does not perform synthesis for hardware.

Do $display and $monitor work?

Yes, system tasks like $display, $monitor, $write, and $strobe work and their output appears in the output panel.

Can I use always blocks?

Yes, always blocks with sensitivity lists are fully supported for modeling combinational and sequential logic.

Can I instantiate modules?

Yes, you can define multiple modules in a single file and instantiate them to build hierarchical designs.

Can I generate VCD output?

VCD output support is limited. While $dumpfile and $dumpvars compile, the generated VCD files cannot be downloaded or viewed as waveforms in this environment.

Verilog Compiler