HDLBits
Solve short Verilog circuit problems checked by simulation
HDLBits is a collection of small digital circuit exercises in Verilog. For each problem you write a module in the browser and submit it. The site simulates your circuit against a set of test vectors, compares it with a reference solution, and shows you where the waveforms differ.
Free · No login · Browser · Beginner
About HDLBits
The problems start with wires and gates and move through combinational logic, sequential logic, state machines, reading simulations and writing testbenches. It trains hardware design thinking, which is quite different from writing software. A built-in Icarus Verilog simulator lets you try your own code.
It suits students in a first digital logic course and programmers curious about hardware. It is free and you can practise without an account; logging in saves your progress across browsers.
On Breakpoint since 28 Oct 2026.
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