PLC Simulator
Free — no install

Ladder Logic Simulator, Free

Write, simulate, and auto-grade ladder logic in any browser. IEC 61131-3, Allen-Bradley, and Siemens dialects — no install, no trial clock.

Try it now — no signupBrowse scenarios →

The short answer

Can you learn ladder logic for free?

Yes — you can learn ladder logic completely free, in a browser, without buying a PLC or installing vendor software. Contacts, coils, seal-in rungs, timers, and counters behave identically in a scan-cycle simulator, and auto-graded test cases tell you whether your program actually works. The free tier here never expires and needs no credit card.

What you cannot skip is deliberate practice: reading a spec, writing the rung, running the grader, and fixing what failed. The six-step path below sequences the free graded scenarios on this site in the order the concepts build — the same order our paid curriculum uses. Reference pages for ladder logic symbols and worked ladder logic examples are free too.

The path

How to learn ladder logic free, in 6 steps

Every scenario linked below is on the free tier and auto-graded. Budget a few short sessions per step and don't move on until the grader shows all tests green.

  1. 1

    Open the editor — no signup

    Wire one normally open contact to one coil and toggle the input while the simulator runs. Feeling the scan cycle respond is the whole lesson.

    Try the editor now →

  2. 2

    Pass your first graded scenario

    Switch → light: one rung, graded against test cases. On our platform this is where everyone starts — about 80% of completed attempts pass it.

    Switch & light scenario →

  3. 3

    Combine contacts: AND, OR, NC

    Series contacts (AND), parallel branches (OR), and normally closed logic — the three moves that make up most real interlocks.

    AND logic scenario → · OR logic · NC contact

  4. 4

    Crack the seal-in (latch) rung

    Motor start-stop with a seal-in branch — the first rung that forces you to think in scan cycles instead of straight lines. Expect to fail it a few times; the grader tells you exactly which test broke.

    Motor start-stop scenario → · Latch basics · Latch with stop

  5. 5

    Add time and count: TON timers, counters

    Delays and part-counting are the backbone of real machine sequences — and where the grader’s timing test cases start to matter.

    TON delay scenario → · Counter scenario

  6. 6

    Capstone: the traffic light sequence

    A full timed sequence combining everything above. Create a free account (no credit card) to save your programs and track which steps you’ve passed.

    Traffic light scenario → · Save progress free

The editor — runs in your browser tab

PLC Simulation Software — Ladder EditorStartStop_NCMotorMotorRung 0001// Motor start-stop seal-inTEST RESULTSTC1 — Start pressed, Stop NC: Motor = ONTC2 — Start released, Motor sealed-in: Motor = ONTC3 — Stop pressed: Motor = OFFTC4 — E-stop (Stop held): Motor stays OFF

Motor start-stop with seal-in — auto-graded test cases show pass/fail per test

Ladder logic symbols the free simulator supports: XIC, XIO, OTE, OTL, OTU contacts and coilsThe core ladder logic symbols side by side: XIC examine-if-closed, XIO examine-if-open, OTE output energize, OTL output latch and OTU output unlatch.XICIfXIOIfOTEEnergizeLOTLLatchUOTUUnlatch
The ladder logic symbols you draw in the free simulator.
A ladder logic rung the free simulator executes and auto-grades each scanA basic ladder logic rung between two power rails: an examine-if-closed contact (XIC) in series driving an output coil (OTE).L1L2] [StartXIC I:0/0LampOTE O:0/0
A complete rung — the simulator runs and grades it rung-by-rung.

What you get

Free tier includes everything you need to start

Free — no credit card
  • Motor start-stop and traffic-light demo — no login required
  • Full ladder editor: XIC, XIO, OTE, OTL, OTU, TON, TOF, CTU, CTD
  • Allen-Bradley tag-style and Siemens-style addressing
  • Auto-graded test cases — pass/fail per test, expected vs. actual output
  • Save progress and unlock extra scenarios with a free account (no credit card)
Pro — full library
  • 170 graded scenarios covering timers, counters, PID, analog I/O, and fault diagnosis
  • Full curriculum with beginner, intermediate, and advanced tracks
  • Certificate of completion for the full scenario track
  • Job-ready interview prep scenarios
See Pro pricing →

How it works

A real simulator, not a toy

The simulator runs a scan-cycle engine in your browser tab — the same read-inputs, execute-program, write-outputs loop a real PLC runs. Your ladder program is compiled to an instruction set that the engine executes rung-by-rung, updating coil states and timer accumulators each scan. Animated I/O indicators update in real time so you can see exactly which contacts are energised at each step.

The auto-grader injects predefined input states and verifies that your outputs match the expected values. Each test case reports the exact mismatch — “Motor output was OFF, expected ON at T=500ms” — so you know which rung to fix. This is qualitatively different from watching a simulation: you get scored feedback on whether your program is actually correct.

Which ladder instructions are supported?

The IEC 61131-3 core set: XIC (normally open contact), XIO (normally closed contact), OTE (output coil), OTL/OTU (set/reset coils), TON, TOF, TP (timers), CTU/CTD (counters), comparison instructions (GT, LT, EQ), and arithmetic blocks. The Allen-Bradley dialect adds tag-based addressing; the Siemens dialect adds absolute and symbolic address styles.

No install, no Java, no ActiveX

The simulator has run entirely in the browser since day one. There is no plugin, no download, and no trial expiry. It works on Chrome, Firefox, Safari, and Edge — on Windows, Mac, Linux, and Chromebook. If you can open this page, you can run the simulator.

PLC scan cycle the free ladder logic simulator runs in your browser tabThe repeating PLC scan cycle: read inputs, execute the ladder logic, update outputs, then housekeeping, looping continuously.1Read Inputs2Execute Logic3Update Outputs4HousekeepingSCANCYCLE
The scan-cycle engine the free simulator runs — read, execute, write, repeat.
Seal-in latching rung you build and auto-grade in the free ladder logic simulatorA seal-in latch rung: a Start contact in parallel with a Hold contact, in series with a normally-closed Stop contact, driving an output coil.StartHold (seal)StopMotor
The seal-in (latch) rung — the first program most learners write.
TON timer the free ladder logic simulator executes and grades with timing test casesA TON on-delay timer: the accumulated time bar ramps up toward the preset value, and the done (DN) bit turns on when the accumulator reaches preset.TONPRE 5000ACCACC ramps to PREPREDNdone bit
TON / TOF / TP timers — supported and graded against timing test cases.

Start your first scenario — free, right now

No credit card. No install. No trial clock. The free tier does not expire.

Try it now — no signupBrowse all scenarios →

From our grading data

What actually happens when people learn ladder logic here

These figures come from our own simulator's aggregate grading logs as of 10 July 2026 — not estimates.

  • 10,272

    auto-graded ladder logic attempts run on the simulator to date.

  • 80%

    of completed graded runs pass the first scenario (switch → light): 2,116 passes out of 2,634 completed runs. Starting really is easy.

  • 19%

    of completed graded runs pass the motor start-stop seal-in scenario (127 of 679). The latch is where ladder logic stops being obvious — plan to iterate.

  • 7 in 10

    recorded first passes happen on the very first graded run (1,493 of 2,149 first-passes reached within ten runs) — instant grading feedback shortens the loop.

“The seal-in rung is where ladder logic clicks. Fewer than one in five completed attempts at motor start-stop pass — not because it's hard, but because it's the first rung where you have to think in scan cycles instead of straight lines. Free practice with instant grading is exactly how you get through that wall.”
— Paul, instructor and creator of PLC Simulation Software
Ladder logic simulator FAQ

Common questions about free ladder logic simulators.

Yes. You can learn ladder logic completely free in a browser — no PLC hardware, no vendor software license, no credit card. Contacts, coils, seal-in rungs, timers, and counters behave identically in a scan-cycle simulator, and auto-graded test cases tell you whether your program actually works. This page lays out a six-step free learning path from your first rung to a timed traffic-light sequence.

Runnable simulator field guide

Free ladder logic simulator tool: test checklist

Direct answer

The learner can predict rung continuity, change inputs, observe outputs and test a start, stop, timer, counter or edge case from a known state.

Written for pLC beginners who want to enter, run and observe a small ladder program without installing vendor engineering software.

System map / 02

NODE 01observable

Scenario setup

The supported instruction subset, I/O tags, scan model, initial state, machine requirement and acceptance checks.

NODE 02observable

I/O and state map

Input state through rung evaluation, internal instruction state and output tags to visible equipment behavior.

NODE 03observable

Normal run

One start-stop and timer program run over repeated scans from a clean reset.

NODE 04observable

Boundary run

Simultaneous commands, edge events, timer boundaries, retained state, reset and unsupported syntax.

NODE 05observable

Injected fault

A contact sense, branch, timer, counter, edge, output-owner or feedback defect.

NODE 06observable

Target check

The accepted behavior recreated and tested in the required target software and controller.

Answer surface / 07

Is this ladder logic simulator free?

The public tool provides a browser-based learning path without a vendor software install; current account and feature limits are shown on the product and pricing pages.

Can an online ladder simulator replace Studio 5000 or TIA Portal?

No. It teaches transferable behavior. Native projects, firmware, communications and target validation require the official toolchain.

Continue the signal path / 08