Like HDLBits, but you wire the circuits by hand
HDLBits is a collection of small digital circuit design exercises with an online judge, made by Henry Wong, who spent seven years as a teaching assistant in digital logic and computer organization courses during his Ph.D. at the University of Toronto. You solve each problem by writing a Verilog module in the browser, and it is checked by simulating it with a set of test vectors against a reference solution, with immediate feedback. The problems run from the Verilog language itself through combinational and sequential logic to reading simulations and writing testbenches, and an account is optional, needed only to track your progress. If that is what brought you here, digiwleea is a free, in-browser alternative with a different angle: you build a computer from the transistor up.
What HDLBits is good at
It is excellent practice for anyone learning Verilog for a digital design course or an FPGA project: short, focused problems, a real simulator behind every check, instant feedback on where your circuit differs from the reference, and a page for running your own simulations with Icarus Verilog. It shares its home, 01xz.net, with the CPUlator computer system simulator. (digiwleea is an independent project, not affiliated with HDLBits.)
How digiwleea is different
HDLBits teaches digital design through a hardware description language: you describe the circuit as text and a simulator checks it. digiwleea teaches it by building: you wire the circuit on a canvas, starting from CMOS transistors, and watch every wire change as it runs, then compose gates into adders, an ALU, registers, RAM and control logic, ending with an 8-bit CPU, in a guided 40+ level course with an AI tutor (Wleea). A finished circuit can be exported as VHDL, and the free Verilog lessons describe the same circuits in code, but digiwleea does not check Verilog that you write. HDLBits is the better pick for learning Verilog and practicing for HDL coursework; digiwleea is the better pick for building the intuition for what that Verilog turns into, and the two work well together.
| HDLBits | digiwleea | |
|---|---|---|
| You describe circuits as | Verilog modules | Gates and wires on a canvas |
| Checked by | Simulation against a reference, with test vectors | The real simulator: truth tables and clocked timelines |
| Topics | Verilog, combinational and sequential logic, simulations, testbenches | Transistors, gates, arithmetic, memory, an 8-bit CPU |
| HDL | Verilog is the whole point | VHDL export, plus free Verilog lessons |
| Runs in | The browser | The browser |
| AI tutor | No | Yes (Wleea) |
No sign-up is needed to start: open the lab and place your first transistor, or read the free theory course. The account (and the AI tutor) are optional.
See for yourself: build a logic gate from transistors in the simulator, then follow the path from sand to an 8-bit CPU.
Open the digiwleea lab →Frequently asked
Is digiwleea a good HDLBits alternative?
Yes, if you want to understand digital logic from the ground up. digiwleea is a free, in-browser simulator with a guided 40+ level course where you build every gate from CMOS transistors and work up to a real 8-bit CPU, with an AI tutor to help.
Is digiwleea free?
The sandbox lab and the first act of the course are free and need no sign-up. An optional account adds the AI tutor and cross-device sync; the full course and expanded AI tutoring are included in the monthly or annual Premium subscription.
Do I need to install anything?
No. digiwleea runs entirely in your browser, on desktop or mobile, and works offline once loaded.