Can this replace Studio 5000 Logix Emulate or PLCSIM?

For firmware validation, cycle-accurate timing tests, and production commissioning dry-runs: no. Those require vendor firmware running in a VM, and for that use case you need Rockwell Logix Emulate or Siemens PLCSIM. For learning ladder logic, testing control logic offline, teaching PLC programming, or interview prep: yes — this is faster to start, free, and runs in any browser.

Is the PLC simulator free?

Yes. The free tier includes two complete scenarios — Traffic Light and Motor Start/Stop — with no credit card and no trial clock. Upgrade to Basic or Pro when you want access to all 40 scenarios, 18 structured lessons, interview-timer mode, and downloadable certificates.

Can I test my existing Allen-Bradley or Siemens code here?

You can paste Allen-Bradley RSLogix-style or Siemens TIA Portal-style ladder logic into the editor and run it against a scenario. The simulator normalises all three dialects (IEC, AB, Siemens) into a common execution model. It will not run native .ACD or TIA project files — you copy the logic text. For validating production project files against real firmware, use Logix Emulate or PLCSIM.

Does the simulator run cycle-accurate timing?

No. The scan cycle is simulated in the browser, not cycle-accurate to specific hardware. TON, TOF, and TP timers behave correctly relative to the simulated scan, but the absolute timing will not match a real ControlLogix or S7-1500 scan rate. If your application requires cycle-time validation against specific hardware specs, that is a genuine firmware emulator use case.

Is this suitable for learning and interview prep?

Yes — that is the primary use case. Forty auto-graded scenarios cover the machine types that appear in PLC programmer interviews: motor start/stop, conveyor sort, tank fill, PID temperature control, batch sequencing, and more. Six interview tracks with a timed mode and downloadable certificates let you demonstrate competence to a hiring manager without access to vendor hardware.

Can this replace Studio 5000 Logix Emulate or PLCSIM?

For firmware validation, cycle-accurate timing tests, and production commissioning dry-runs: no. Those require vendor firmware in a VM, and for that you need Logix Emulate or PLCSIM. For learning ladder logic, testing control logic offline, teaching, or interview prep: yes — this is faster to start, free, and runs in any browser without a Windows machine or paid license.

Is the PLC simulator free?

Yes. The free tier includes two complete scenarios — Traffic Light and Motor Start/Stop — with no credit card and no trial clock. Upgrade to Basic or Pro for all 40 scenarios, 18 structured lessons, interview-timer mode, and downloadable certificates.

Can I test my existing Allen-Bradley or Siemens code here?

You can paste Allen-Bradley RSLogix-style or Siemens TIA Portal-style logic into the editor and run it against a scenario. The simulator normalises all three dialects into a common execution model. It will not run native .ACD or TIA project files — you copy the logic text. For validating production project files against real firmware, use Logix Emulate or PLCSIM.

Does the simulator run cycle-accurate timing?

No. The scan cycle runs in the browser, not cycle-accurate to specific hardware. TON, TOF, and TP timers behave correctly relative to the simulated scan, but absolute timing will not match a real ControlLogix or S7-1500 scan rate. If your application requires cycle-time validation against specific hardware specs, that is a genuine firmware emulator use case.

Is this suitable for learning and interview prep?

Yes — that is the primary use case. Forty auto-graded scenarios cover the machine types that appear in PLC programmer interviews: motor start/stop, conveyor sort, tank fill, PID temperature control, batch sequencing, and more. Six interview tracks with timed mode and downloadable certificates let you demonstrate competence without access to vendor hardware.

Does it run online without installing anything?

Yes. It is a fully online PLC emulator alternative — the scan cycle, editor, IO table, and machine canvas all run in the browser. There is nothing to download and no Windows requirement, so it works on macOS, Linux, Chromebooks, and locked-down lab machines where a vendor emulator like PLCSIM or Logix Emulate cannot be installed.

How does this compare to OpenPLC, PLC-Fiddle, or CODESYS?

They solve different problems. CODESYS and OpenPLC are full IEC 61131-3 runtimes you install and configure yourself — powerful, but you build your own machines and test logic. PLC-Fiddle is a lightweight browser ladder editor with no graded machines. This platform sits between them: it runs in the browser like PLC-Fiddle, but ships 40 physics-backed machine scenarios with a hidden test harness that grades your logic — built for learning and interview prep rather than configuring a runtime.

PLC Simulator

Free alternative

PLC Emulator — Free, Browser-Based Simulator Alternative

Most ladder logic testing doesn't need a true firmware emulator — a simulator solves the same problem free, in the browser.

Open the simulator →Sign up free

How it feels

Built to build intuition.

A browser tab that behaves like a real PLC bench — without the hardware budget.

Real machine physics

Every scenario simulates real equipment. Tanks fill, motors spin, valves modulate — driven by your actual ladder logic.

Live I/O experimentation

Toggle inputs by hand to see how the PLC responds. No wiring, no hardware — just click and learn.

Certificate-backed interview prep

Pass an interview track and earn a downloadable PDF certificate. Pro users get solution walk-throughs with expert commentary on every scenario.

This is our PLC simulator — equivalent to what most “PLC emulator” searches actually want.

An online PLC emulator alternative that runs entirely in the browser — no Windows, no install, no license key.

The honest distinction

PLC Emulator vs Simulator — What's the Difference?

A PLC emulator runs the actual firmware of a specific controller in a virtual machine. Rockwell's Studio 5000 Logix Emulate, for example, executes real ControlLogix firmware on your Windows PC — cycle-accurate scan times, vendor-identical instruction behaviour, hardware-specific diagnostic codes. Siemens PLCSIM does the same for S7 and S7-1500 firmware inside TIA Portal. These are genuine firmware emulators: the same binary that runs on the physical rack runs inside the VM.

A PLC simulator replicates the behaviour of a PLC without running vendor firmware. It parses your ladder logic or Structured Text into an intermediate representation, schedules a scan cycle, evaluates every rung against an IO table, and drives a software model of the machine. The timing is not cycle-accurate to specific hardware. The instruction set is modelled, not firmware-identical. But for the vast majority of use cases — learning ladder logic, testing control sequences offline, teaching PLC programming to a class, preparing for a technical interview — a simulator gives you everything you need without the Windows dependency, the multi-gigabyte install, or the paid vendor license.

Both a real PLC and a simulator run the same loop: read inputs → execute logic → update outputs → repeat. The simulator runs it in your browser instead of on firmware.

Whether it runs on a real ControlLogix rack, inside Logix Emulate, or in our browser-based simulator, the scan cycle is identical in shape: read every physical and internal input into an image table, solve each rung top-to-bottom and left-to-right, write the results to the output table, then loop. What a true emulator adds is firmware-exact timing for that loop. What a learning simulator gives you is the same logical behaviour with instant feedback — which is precisely what you want when the goal is to understand the logic, not to certify a scan time.

The architecture a PLC emulator reproduces: CPU, input/output modules, and the IO image table. Our simulator models the same structure in software.

A single ladder rung: input contacts in series and parallel feeding an output coil. The simulator solves each rung left to right, exactly as a real PLC scan does.

Our product is a simulator. It runs your ladder logic through a scan cycle, drives a physics model of a real machine, and grades your output against a scripted test harness. It supports IEC 61131-3, Allen-Bradley, and Siemens dialects in the same editor, free, in any browser. For the “I need to test my PLC code without hardware” use case — which is what most people searching for a free PLC emulator online actually want — this is the right tool. We will tell you clearly below when it is not.

Be honest about it

When You Need a True PLC Emulator

There are use cases where only a firmware emulator will do. If any of the following apply to your project, use the vendor tool.

Production code validation for high-reliability systems. Safety-rated or regulatory-certified code must be validated against the exact firmware that runs on the production rack.
Cycle-time tuning against specific hardware. If your application depends on a specific scan rate or instruction execution time, you need firmware running in a VM, not a browser-simulated scan.
Firmware-specific bug reproduction. Hardware-specific edge cases in instruction handling require the actual firmware to reproduce reliably.
Vendor-approved commissioning dry-runs. Some project contracts require a PLCSIM or Logix Emulate acceptance test before site commissioning.

Vendor firmware emulators for these use cases:

Rockwell Studio 5000 Logix Emulate — runs real ControlLogix firmware, Windows-only, approximately $1,500 license. [ESTIMATE — verify current Rockwell pricing]
Siemens PLCSIM — bundled with TIA Portal, Windows-only, TIA Portal license approximately $1,500+. [ESTIMATE — verify current Siemens pricing]
Beckhoff TwinCAT — runtime license required, Windows-only.

The right tool for most cases

When a Simulator Is What You Actually Need

If your goal is any of the following, a simulator — ours in particular — is faster, cheaper, and more accessible than a firmware emulator.

Learning ladder logic or Structured Text from scratch.
Students practising machine control scenarios outside the lab — no admin-locked installs, no per-seat licenses.
Interview preparation — testing your logic against graded scenarios before a technical assessment.
Verifying logic changes offline before a commissioning window, when cycle-accurate timing is not a requirement.
Building a portfolio of working PLC programs to show a hiring manager.
Teaching PLC programming to groups — browser-based means Chromebook-friendly, no IT involvement.
Exploring how industrial control patterns work (interlocks, sequencers, PID loops) without physical hardware.

What you get

Features of Our PLC Simulator (the Emulator Alternative)

Six reasons this simulator covers the same ground as a PLC emulator for learning, teaching, and offline logic development.

Three dialects in one editor

IEC 61131-3 Structured Text, Allen-Bradley RSLogix-style, and Siemens TIA Portal-style. Switch dialect on any scenario without losing your code.

40 auto-graded scenarios

Every scenario ships with a scripted test harness that evaluates correct sequencing, interlock behaviour, and timing windows — then returns pass/fail with a specific failure reason.

Browser-based — any OS

No install, no Windows dependency, no vendor license key. Works on Chrome, Firefox, Safari, Edge — including Chromebooks and macOS.

Free tier, no credit card

Two complete scenarios free with no account required. Not a limited demo — full scan cycle execution, IO table, and physics canvas.

Hidden test cases grade your logic

You see the objective, not the test suite. The grader evaluates your program against scenarios it was not written for — the same pressure as a real interview coding challenge.

Structured Text + ladder editor

Monaco-based editor with syntax highlighting, VAR block support, and the full IEC 61131-3 instruction set: XIC, XIO, OTE, TON, CTU, R_TRIG, PID, and more.

One editor, three dialects — IEC 61131-3, Allen-Bradley, and Siemens

A vendor firmware emulator locks you to one ecosystem — Logix Emulate runs RSLogix/Studio 5000 code, PLCSIM runs TIA Portal code. This simulator instead normalises three dialects into one execution model, so you can write the same control problem in standards-based IEC 61131-3 Structured Text, in Allen-Bradley RSLogix-style ladder, or in Siemens TIA-style ladder, and run all three against the identical graded scenario. That makes it a practical way to learn the patterns that transfer across every vendor, not just one.

The IEC 61131-3 language family. This simulator runs Ladder and Structured Text, the two dialects you meet most often across Allen-Bradley and Siemens.

Write standards-based Structured Text in the Monaco editor — VAR blocks, IF/THEN, and the full instruction set — and run it on the same scan cycle as ladder.

Inputs and outputs are tracked in a live IO table you can watch update every scan, exactly as you would on real hardware.

Comparison

Comparing PLC Emulators and Simulators

An honest side-by-side. Each product listed here does something useful. The differences are in type, cost, and access friction.

Product	Type	License	Install	Scenarios
Studio 5000 Logix Emulate	Firmware emulator	~$1,500 [ESTIMATE]	Windows	Custom
Siemens PLCSIM	Firmware emulator	~$1,500+ with TIA [ESTIMATE]	Windows	Custom
This platform	Simulator	Free tier available	None (browser)	40 pre-built
PLC-Fiddle	Simulator	Free	None (browser)	Minimal
OpenPLC	Simulator / runtime	Free	Linux / Windows	User-built

Pricing estimates are approximate and subject to change. Verify current licensing costs directly with Rockwell Automation and Siemens. This site is not affiliated with or endorsed by any vendor listed in this table.

No download

How to Start the PLC Emulator in Under a Minute

A vendor firmware emulator like Logix Emulate or PLCSIM is a multi-gigabyte Windows install behind a license server. This browser-based simulator skips all of that — there is nothing to download, no Windows requirement, and no key to enter.

1.Open a free scenario such as the Motor Start / Stop or Traffic Light scenario — no account needed to try them.
2.Write your control logic in the editor — ladder rungs or IEC 61131-3 Structured Text — in your chosen dialect.
3.Press Run. The scan cycle starts, the IO table updates live, and the simulated machine reacts on screen.
4.The hidden test harness grades your program and tells you exactly which case passed or failed — iterate until it is green.

The first program most people run: three-wire motor control with seal-in. Build it in ladder, press Run, and watch the contactor latch in the simulated IO table.

Once the basics click, most scenarios add a timing element. The emulator runs the standard IEC 61131-3 timers — TON (on-delay), TOF (off-delay), and TP (pulse) — on the same scan, so a timer's accumulated value advances every cycle exactly as it would on a real controller.

On-delay (TON), off-delay (TOF), and pulse (TP) timers all run on the simulated scan — accurate relative to the scan, though not cycle-accurate to a specific hardware clock.

Start here

Core Scenarios to Try

Six of the 40 scenarios — covering the machine types that appear most often in PLC programmer assessments and on the shop floor. Free-tier scenarios open without an account.

Motor Start / Stop

Three-wire control with seal-in, E-stop, and thermal overload interlock.

Traffic Light

Four-way signal with timer chain and all-red safety interlock phase.

Conveyor Sort

Photo-eye sort station with part counters and reject actuator output.

Tank Fill Station

Level sensors with hysteresis control and latched high-level alarm.

PID Temperature

Closed-loop temperature control with tuning parameters and setpoint ramp.

Batch Mixer

Multi-step sequencer with ingredient timing and agitator interlock.

Showing 6 of 40 scenarios. View all 40 →

FAQ

Common questions about PLC emulators and simulators.

It is a simulator, not a firmware emulator. A true PLC emulator — Rockwell Studio 5000 Logix Emulate or Siemens PLCSIM — runs actual controller firmware in a virtual machine, cycle-accurate and vendor-identical. Our platform simulates the logic layer: your ladder logic executes on a scan cycle, drives a physics model, and returns auto-graded results. For learning, teaching, and most logic-testing use cases, that is exactly what you need.

Try the PLC Simulator

No install. No license. Open the Traffic Light scenario right now without an account, or sign up free to save your progress.

Try the simulator →Sign up free

Rockwell Automation, Studio 5000, and Logix Emulate are trademarks of Rockwell Automation, Inc. Siemens and PLCSIM are trademarks of Siemens AG. Beckhoff and TwinCAT are trademarks of Beckhoff Automation GmbH & Co. KG. This site is not affiliated with or endorsed by any of these companies.