PLC Simulator
IEC 61131-3 compliant

Ladder Diagram Simulator — Free & IEC-Compliant

Draw contact/coil rungs and execute them against virtual inputs and outputs. IEC 61131-3 notation throughout — NO contacts, NC contacts, TON, CTU, R_TRIG — all in your browser with no install.

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See the actual product

Watch a real PLC program run in the browser.

This is recorded from the working simulator—not a conceptual mockup. See the editor, live I/O and industrial scenario respond together before you create an account.

Free PLC Simulator — program a PLC in your browser

What the footage proves

Program the real simulator

Write ladder or structured text, run the scan, toggle live I/O and see the machine state respond.

Learn inside industrial scenarios

Practice motors, tanks, conveyors, alarms and interlocks instead of watching a decorative animation.

Get a guided next step

Use checks, explanations and structured learning paths to move from a first rung to job-relevant control work.

Run your first PLC program free →

No install. No card. Start with a working circuit.

A ladder diagram simulating a motor start-stop seal-in. No install. Watch contacts pass power, timer accumulators tick, and outputs energise in real time.

Ladder diagram 101

What is a ladder diagram simulator?

A ladder diagram simulator is software that lets you draw contact/coil rungs and execute them against virtual inputs and outputs, so you can verify the program without real hardware. You define your variables, wire up the rungs, press Run, and watch the IO image update scan by scan — exactly as it would on a physical PLC.

Paper and textbook exercises teach you ladder diagram syntax. A simulator teaches you to read runtime behavior — why a seal-in rung stays energised after the START button is released, how a TON timer accumulates elapsed time on every scan, and where race conditions can appear when two rungs write to the same coil in different orders. That understanding is what separates someone who has studied a diagram from someone who can actually commission one.

Traditional ladder diagram tools — CoDeSys, Siemens TIA Portal, Allen-Bradley Studio 5000, Festo FluidSIM — are desktop installs tied to specific operating systems, hardware dongles, or expensive licenses. A browser-based simulator removes every one of those constraints. If you can open a URL, you can run a ladder diagram.

Instruction set

What ladder diagram notation is covered?

Every instruction below is implemented to the IEC 61131-3 specification. Contact and coil symbols use IEC notation; AB and Siemens aliases are mapped to the same execution primitives under the hood.

Contacts
  • -| |- normally open (NO)
  • -|/|- normally closed (NC)
  • -|P|- rising edge (R_TRIG)
  • -|N|- falling edge (F_TRIG)
Coils
  • -( )- standard output coil
  • -(S)- set (latch)
  • -(R)- reset (unlatch)
  • -(/)- negated output
Timers
  • TON — on-delay
  • TOF — off-delay
  • TP — pulse timer
Counters
  • CTU — count up
  • CTD — count down
  • CTUD — up/down
Compare
  • EQ, NE (equality)
  • GT, GE, LT, LE (relational)
Math
  • ADD, SUB, MUL, DIV, MOD
Flow Control
  • JMP / LBL (program flow)
  • Nested rungs (parallel branches)
Advanced
  • PID function block
  • Comparison blocks on analog tags
Dialect support

Three dialects of ladder diagrams supported

Ladder diagram conventions vary by PLC vendor. A Siemens technician writes contacts as --| |-- and refers to the program as a "ladder diagram" per IEC 61131-3. An Allen-Bradley technician calls the same thing "ladder logic" and names contacts XIC and XIO. The underlying scan-cycle model is identical; only the notation and instruction mnemonics differ.

This simulator lets you switch dialects on any scenario without rewriting your program. The execution engine is the same — you are learning the same concepts regardless of which syntax you use.

IEC 61131-3Default

The international standard. Contact symbols -| |-, coil symbols -( )-, timer and counter names TON / CTU. Preferred by Siemens, Beckhoff, CODESYS, and European academic curricula.

Allen-BradleySupported

Rockwell Automation / Studio 5000 style. Contacts named XIC and XIO, coils named OTE / OTL / OTU. Dominant in North American manufacturing. The dialect most US PLC job listings specify.

Siemens TIA PortalSupported

Siemens-specific syntax for LAD (Ladder) programs. Contact and coil symbols follow IEC conventions but use Siemens data types, addressing, and function block signatures.

Practice scenarios

Ladder diagram scenarios to practise with

Each scenario loads a machine simulation and a set of auto-graded objectives. Write your ladder diagram, press Run, and the test harness tells you which objectives pass and which fail. No manual marking.

Motor Start-Stop

The canonical three-wire seal-in circuit. A START push-button latches the motor contactor through its own auxiliary contact. An E-stop and thermal overload on normally-closed contacts break the rung. The foundational ladder diagram every technician must know.

BeginnerSafetyCoils

Traffic Light

Sequential timing with TON timers. Green, amber, red phases driven entirely by timer .Q outputs and reset logic. Add a pedestrian walk-request input and watch the IEC 61131-3 rung structure handle event priority.

BeginnerTimersSequencing

Conveyor Sort

Sensor-based diverter logic. A photoelectric sensor detects item presence; a compare instruction checks a tag count; a solenoid diverter fires on the correct items. Introduces conditional branching inside a ladder diagram.

IntermediateCompareSensors

Tank Fill

Analog level comparison using IEC compare instructions (GE, LE) against a simulated 4–20 mA level transmitter. Level high and level low switch points drive fill and drain valves. A realistic SCADA-style ladder diagram in the browser.

IntermediateAnalogCompare

Elevator

State-machine control across multiple floors. Floor-call and direction bits drive a sequencer through IDLE, MOVING, and DOOR states. One of the more complex ladder diagrams in the set — good preparation for multi-step machine control interviews.

AdvancedState MachineSequencing

E-Stop Reset

IEC 61131-3 safety circuit topology. Latching fault bits, monitored reset push-button, and a guard that prevents auto-restart after an E-stop. The ladder diagram structure here follows the reasoning examiners expect in functional safety discussions.

IntermediateSafetyIEC 62061
Comparison

Comparing ladder diagram simulators

Most ladder diagram tools are either expensive, Windows-only, or both. Here is an honest comparison of the options available.

ToolCostPlatformStandardScenarios
FluidSIM~€200Desktop (Windows)Festo-specific—
LogixPro$200+Desktop (Windows)Allen-Bradley only~10
CoDeSysFree to €€€Desktop (Win/Mac)IEC 61131-3None built-in
PLC-FiddleFreeBrowserLimitedLimited
PLC Simulator (this)Free / ProBrowser (any OS)IEC 61131-3 + AB + Siemens140 published
FAQ

Ladder diagram simulator — frequently asked.

Yes. Run the guided first program without an account, then create a free account for 32 practice scenarios and beginner labs. Pro unlocks all 170 published scenarios, guided paths, solutions, quizzes and 6 interview tracks.

Related: PLC ladder logic simulator · PLC simulator · PLC programming simulator · PLC training · draw the control wiring diagram (CircuitDiagramMaker)

Open the ladder diagram simulator.

No install. No license. Start with a guided switch-to-light program, then continue through 10 free beginner PLC labs and a resumable skill path.

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Runnable simulator field guide

Ladder diagram simulator: test checklist

Direct answer

The user can build a rung from a written requirement, predict continuity, run it and connect the output state to an observable I/O or machine result.

Written for pLC beginners and technicians who want to draw contacts, coils, branches, timers and counters and observe the evaluated result.

System map / 02

NODE 01observable

Scenario setup

The required inputs, state, outputs, feedback, stop priority and restart policy.

NODE 02observable

I/O and state map

Diagram symbols and tags through scan evaluation to output and machine behavior.

NODE 03observable

Normal run

A seal-in, interlock, timer and counter pattern executed from a clean state.

NODE 04observable

Boundary run

Parallel paths, inverted logic, simultaneous events, timer boundaries, retentive state and restart.

NODE 05observable

Injected fault

A duplicate coil, missing branch, wrong contact sense or stale feedback signal.

NODE 06observable

Target check

Tested behavior documented and recreated in the selected vendor environment.

Continue the signal path / 08

Real ladder diagram simulator footage

See this exact skill in the working simulator.

Watch the real browser product respond to the task on this page, then try the same practical workflow yourself. No slides, concept mockups, install, or credit card.

Try this in the browser
Ladder Diagram Simulator — Drag, Name, Run and Test

Core PLC simulator path

Choose the right starting point, then run a real task

Compare the product scope, open the no-install workbench, study the instruction behavior and progress into structured practice.