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Open Model Lab

Circuit Builder

Build a live circuit and explain what it is doing.

Free-build, inspect live values, and keep the three-panel bench in view.

Start

Guided mode

Ready to check

Complete a battery-resistor loop

Build one closed path: battery -> resistor -> back to battery.

Workspace

Drag parts, rotate them in the inspector, and pan the canvas by dragging empty space.

Zoom out from the current centered workspace view. Shortcut: minus. Ctrl/Cmd plus wheel zooms around the pointer.Zoom in on the current centered workspace view. Shortcut: plus. Ctrl/Cmd plus wheel zooms around the pointer.Workspace is already at the default zoom and pan. Shortcut: 0.Add at least one component before fitting the workspace view.Add at least one component before clearing the workspace.
Local draftLocal saves work without sign-in. Sign in and upgrade to Supporter for cross-device account saves.
View
78% zoom0 parts0 wiresPan by dragging empty space32 px snap grid

Start with a source and one load

Click a palette item to add it here, then connect terminals with the wire tool.

Example: battery -> resistor -> back to the battery for a complete loop.

Add parts

Open the component library, add parts, or switch to the wire tool before using save and export tools.

Inspector

Component details, live readouts, warnings, and graph panels move here on smaller screens.

Inspector

Select a part to inspect it

The inspector explains what each symbol means, which properties you can edit, and how the part is behaving inside the current circuit.

1. Add a source and one load.

2. Use the wire tool to connect terminals.

3. Select a part for edits and live readouts.

The current circuit solves cleanly. Select a component to see its local explanation and computed values.

Environment

25 C35%

Ambient-linked thermistors follow temperature and ambient-linked LDRs follow light intensity. Manual mode ignores these sliders.

Status and tools

Nothing selectedEmpty workspaceSolver readySelect modeNo history yetLocal draft
No undo step is available yet. Shortcut: Ctrl or Command plus Z.No redo step is available yet. Shortcut: Ctrl or Command plus Y, or Ctrl or Command plus Shift plus Z.
Select a component before rotating. Shortcut: R.Select a component or wire before deleting. Shortcut: Delete or Backspace.

Diagram export stays disabled until the workspace contains at least one component. JSON state export still works for an empty workspace.

Select mode is active. Click parts or wires to inspect, move, rotate, or delete them.

Shortcuts: W starts wiring, +/- zooms, Ctrl/Cmd+wheel zooms around pointer, F fits, 0 resets view, Ctrl/Cmd+Z undoes, Ctrl/Cmd+Y redoes.

Save and reopen circuits

Named local saves live here. Autosave draft recovery stays separate and only protects against accidental loss.

Save locally keeps reusable browser-only circuits here. Account saves stay in the account section below, and autosave draft recovery stays reserved for accidental refresh loss.

0 local
No named saved circuits yet. Use Save locally to keep a reusable circuit here. Autosave drafts stay separate and are only for recovery after accidental loss.

Account saved circuits

Account saves are cross-device named circuits for eligible signed-in users. They stay separate from local browser saves and the autosave recovery draft.

Supporter

Account-saved circuits

Account-backed saved circuits reopen your custom builds across devices while local saves and autosave recovery remain available in this browser.

Sign in only if you want to save and sync the same core learning progress across devices later. Supporter checkout stays separate.

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Solver notes and model assumptions

This v1 builder prefers an explicit, teachable DC steady-state model over perfect electronics fidelity.

Batteries are ideal voltage sources. Resistors, bulbs, thermistors, LDRs, meters, closed switches, and intact fuses are linear or near-linear elements in the steady-state solve.
Capacitors are treated as open circuits after settling. Diodes use a simplified threshold model, bulbs are resistive loads, and fuses trip instantly once the steady-state current exceeds their rating.
Wires collapse terminals into shared nodes, so branch currents and voltage drops come from the same graph-based circuit solve instead of separate per-widget math.
SVG and JSON export both use the same document model, so future formats can reuse this pipeline without changing the builder state shape.