Logits is a place to build digital circuits and see what they do. Put gates on the canvas, connect their pins, and flip a switch. You can follow each signal as it moves through the circuit, down to simulated nanoseconds.
The canvas is the working circuit, not just a drawing of one.
50 built-in element types · 10 categories · 4-valued signals · buses up to 64 bits
| A flexible set of parts | Start with familiar gates, switches, clocks and displays, then add counters, memory, buses, notes or your own reusable subcircuits. |
| Signals move over time | Gates have delays, clocks create edges, and scopes show signal changes beside the circuit. |
| See uncertain signals | Signals can be 0, 1, X (unknown or conflict) or Z (floating). Conflicts and uninitialised outputs stay visible instead of silently turning into zero. |
| Shape your wiring | Draw wires at any angle, add and move bends, and branch directly from an existing wire. Undo a wiring gesture in one step. |
| Get repeatable results | Run the same circuit with the same inputs and get the same waveform each time. |
| Keep your work close | Circuits are JSON documents saved in your browser. Export or import them whenever you like; there is no account or backend. |
| Find help in the app | Each part has its own help, including the pins and settings it supports. |
A signal is never a boolean and never a number bitmask. X gets a marker, not
just a colour. The same rule holds everywhere in the UI, so state is never
communicated by colour alone.
Logits comes with twelve example circuits. Open one to try it out, or import it into a project when you want to make changes. Examples are not autosaved, so you can experiment without worrying about changing the original.
| Example | What it shows |
|---|---|
| Gate sampler | Every basic gate driven by the same two switches |
| Half adder | Two bits in, sum and carry out |
| Full adder | Two half adders and an OR, carry chained |
| 2→1 mux | Select picks which input reaches the output |
| SR latch | Cross-coupled NOR gates that remember a bit |
| Same-instant ordering | Two NOR latches released together: one oscillates, one latches |
| Master-slave flip-flop | Two latches in series, clocked on opposite edges |
| Mod-16 synchronous counter | Counts from 0 to 15, then wraps back to 0 |
| Tri-state bus | Two drivers sharing one net, with Z and X |
| Calculator | Keypad calculator with two four-digit operands and a readout |
| Snake | Snake on a 16×16 matrix, with keyboard, RAM and generated food |
| MNIST digit recognizer | A neural network that recognizes handwritten digits |
| Gesture | Action |
|---|---|
| Wheel / two-finger scroll | Pan · Ctrl/Cmd + wheel or pinch zooms at the pointer |
| Click a palette element, then the canvas | Place it. Click the entry again to arm more copies, and up to 6 land as one undo step |
Ctrl/Cmd + K |
Open the command menu and place at the pointer |
| Click a pin, then a second pin | Wire them. Clicks on empty canvas in between drop bends. Esc cancels |
| Right-click a wire and drag | Branch a new wire from that point |
| Drag a wire, or drag a bend handle | Add or move a bend. Drop a bend on its neighbour to straighten |
Space (tap) / . |
Play–pause / single step |
R · Ctrl+D · Ctrl+Z |
Rotate · duplicate · undo |
Tab, then Enter on a pin |
Start and finish a wire from the keyboard |
Ctrl/Cmd + B · Ctrl/Cmd + J |
Toggle the projects and elements sidebars |
Ctrl/Cmd + G |
Make a subcircuit from the selection |
The full list is in artifacts/07-interaction-spec.md.
Requires Bun. Use bun, not npm or pnpm.
bun install
bun run dev # http://localhost:3000bun run test # vitest, node environment
bun run lint # biome check
bun run build # run this before claiming a change compiles
The app is split into three layers, each with a clear job:
src/lib/contains the circuit model and simulator. It has no browser or React dependencies, so circuits can be simulated in plain Node tests.src/state/handles editing, undo, saving and the running simulation.src/components/draws the editor. Nodes can be reached by keyboard, and all canvas views use the same pan and zoom behavior.
Read artifacts/02-architecture.md before moving a file across a boundary, and the ADRs for why any of it is the way it is.
A definition file under src/lib/nodes/, and one line in
src/lib/nodes/registry.ts. That is the entire change:
export const probeNode = defineNode({
type: "io.probe", // part of the save format, stable forever
title: "Probe",
category: "io",
docs: `A numeric readout of a whole bus, in the radix you choose. …`,
defaultParams: { width: 1, radix: "binary" },
view: "readout", // a name, not a component: this layer can't import React
paramsSchema: [
{ key: "width", label: "Bit width", kind: "int", min: 1, max: 64 },
{ key: "radix", label: "Radix", kind: "select", options: [/* … */] },
],
pins: (params) => [
{ id: "in", name: "IN", direction: "in",
width: intParam(params, "width", 1), side: "left", offset: 2 },
],
size: () => ({ width: 6, height: 4 }),
});The palette, the command menu, the inspector form, the help dialog, the netlist and the simulation all pick it up from there. If you find yourself editing the canvas, the engine or the inspector to make an element work, the abstraction is broken, so fix that instead. Start with artifacts/05-node-authoring-guide.md.
Analog and transistor-level simulation. HDL import/export. Real-time collaboration. Accounts, a backend, a database. Logits is a logic canvas, not a schematic-capture tool and not a teaching platform.
Design docs live in artifacts/ and are the source of truth for
intent; src/ is the source of truth for what exists. Start at
artifacts/README.md; the roadmap
carries the current phase and an honest list of known issues.
Built with Next.js 16, React 19, TypeScript strict, Tailwind v4 and Bun.
Logits is source-available, not open source. It is licensed under the PolyForm Noncommercial License 1.0.0.
In plain terms: use it, study it, fork it, change it and share your changes freely for any noncommercial purpose — personal projects, hobby work, teaching, coursework, research. Build whatever you like on top of it for yourself.
What you may not do is use Logits, or the parts that make it Logits, for a commercial purpose — selling it, hosting it as a paid service, or shipping it inside a product you charge for. That needs written permission; ask.
Contributions are welcome under the same terms: open an issue for a bug or a feature request, or send a pull request. CONTRIBUTING.md has how to get set up, the rules that are load-bearing, and how to add a node. By contributing you agree your contribution is licensed to the project under the licence above.
Found a vulnerability? Please report it privately — see SECURITY.md.