PLC Simulator
PLC-Fiddle alternative

A PLC-Fiddle Alternative With Scored Scenarios and Dialects

PLC-Fiddle is great for sketching a rung or two. When you are ready for graded practice, structured text, and Allen-Bradley or Siemens-style code — still in the browser, still free to start — here is what is on offer.

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Opening honesty

PLC-Fiddle is brilliant for one specific job.

We will not pretend otherwise. If you want to sketch a three-rung ladder and share it with someone on Reddit in 30 seconds, open PLC-Fiddle and skip this page. We are for the step after that — when "can you explain seal-in?" has become "can I prove I understand the scan cycle well enough to ship code?"

A browser-based PLC simulator running ladder logic and structured text with no install, the same in-tab workflow as PLC-Fiddle but with auto-graded scenariosA web browser window running a PLC ladder logic simulator with an input/output strip, requiring no installation or download.plcsimulator.app/playno installINPUTSOUTPUTS
Like PLC-Fiddle, everything runs in the browser — no download, no install. We just wrap a scored learning path around it.

Background

What PLC-Fiddle is

PLC-Fiddle is a free browser-based ladder logic sandbox hosted at plcfiddle.com. It launched around 2016 and quickly became the standard recommendation on r/PLC, MrPLC, and AccAutomation for anyone asking "where can I try ladder logic without installing anything?" It supports Boolean, Number, Timer, and Counter variables, a drag-and-drop rung editor, and shareable-link saving.

Cost: free. Signup: none required. Platforms: any modern browser. Development: looks to have slowed in recent years — the core works, but major new features are rare.

Strengths

What PLC-Fiddle does well

Zero friction

No signup. No install. Open a tab, drop rungs, watch them run. The lightest possible way to try ladder.

Shareable programs

Every circuit gets a URL. Pasting your 4-rung attempt into a forum post for help is a one-click action.

Minimalist UI

Absolute beginners are not drowned in menus. The contact-coil-timer mental model is the whole tool.

Ladder logic symbols — normally-open and normally-closed contacts, output coils, timers and counters — the contact-coil vocabulary PLC-Fiddle teaches wellThe 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 contact-coil-timer vocabulary PLC-Fiddle gets you fluent in — the foundation every PLC language builds on.

Where you outgrow it

Where PLC-Fiddle falls short for a serious learner

Ladder only

No structured text, no FBD, no SFC. Those are the other three IEC 61131-3 languages you will need once you work on anything non-trivial.

No dialect switching

Generic ladder only. There is no way to practice Allen-Bradley tag-style or Siemens #Tag conventions — the two dialects that dominate job postings.

No scored scenarios

You type rungs against a blank canvas. There is no auto-grader telling you whether your logic passes the test cases that a real machine would throw at it.

No progress or portfolio

No account, no saved scenario history, no PDF export of completed work. Interview-ready evidence lives in screenshots, not a clean portfolio.

No interview timer

You cannot simulate the 30-minute-per-question pressure that Rockwell and Siemens engineering interviews use.

Maintenance pace

Updates have been rare in recent years. If you hit a bug or want a new feature, the path forward is unclear.

The four IEC 61131-3 languages — ladder diagram, structured text, function block diagram and sequential function chart — three of which PLC-Fiddle does not supportThe five IEC 61131-3 PLC programming languages as chips: Ladder Diagram, Function Block Diagram, Structured Text, Instruction List and Sequential Function Chart.IEC 61131-3 — five languagesLDLadder DiagramFBDFunction BlockSTStructured TextILInstruction ListSFCSequential Func. Chart
PLC-Fiddle covers ladder only. The other three IEC 61131-3 languages are where serious work happens.
A structured text program with IF and timer logic — the text-based IEC language you outgrow PLC-Fiddle's ladder-only sandbox forA small Structured Text code block in an editor: an IF/THEN condition, a TON timer call and assignments, showing text-based PLC programming.main.st — Structured Text1IF Start AND NOT Stop THEN2 Run := TRUE;3END_IF;4DelayTmr(IN := Run, PT := T#5s);5Lamp := DelayTmr.Q;
Structured text (ST) is the first thing you reach for once ladder gets unwieldy — and the first thing PLC-Fiddle cannot do.

Feature comparison

PLC-Fiddle vs plcsimulationsoftware.com

FeaturePLC-FiddleOurs
PlatformAny browserAny browser
Signup requiredNoFree tier — optional; Pro — yes
LanguagesLadder onlyLadder, ST, FBD, SFC
DialectsGenericIEC 61131-3, Allen-Bradley, Siemens
Scored scenariosNo140 published
Progress trackingURL-based onlyAccount-based with history
Interview timerNoYes (Pro)
PDF portfolio exportNoYes (Pro)
Development paceDormant-ishActive weekly updates
PriceFree foreverFree tier + Pro subscription

Pick PLC-Fiddle if…

  • You want the absolute lightest way to try ladder logic.
  • You are sharing a short rung-set in a forum post.
  • You are doing your first-ever exposure to ladder in under 10 minutes.
  • You do not want an account.

Pick us if…

  • You want scored feedback on real scenarios.
  • You want ST, FBD, and SFC, not just ladder.
  • You are prepping for an Allen-Bradley or Siemens interview.
  • You want a PDF portfolio to show an employer.
  • You want progress tracking across sessions.

Online ladder logic simulator

A full online ladder logic simulator — timers, counters and seal-in included

If you found us searching for an online ladder logic simulator, you are in the right place. Like PLC-Fiddle, you draw rungs in the browser with Boolean, Number, Timer and Counter variables and watch them execute live — no install, no licence. Where we go further is turning those rungs into scored practice: every diagram below is a concept you can build and have auto-graded against real test cases, then carry straight into structured text, FBD and SFC.

A TON on-delay timer in ladder logic showing the elapsed and preset values — one of the timer instructions our online ladder logic simulator runs and gradesA 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
Timers (TON/TOF/TP) — PLC-Fiddle has Timer variables; we grade whether you wire them correctly.
An up-counter in ladder logic counting sensor pulses toward a preset, one of the counter instructions exercised in the browser-based simulatorA CTU count-up counter: each input pulse increments the accumulator toward the preset, and the done (DN) bit turns on when count reaches preset.count pulsesCTUPRE 5ACC 3ACCcount toward presetDNdone bit
Counters (CTU/CTD) — count parts on a conveyor and prove the logic resets cleanly.
A seal-in (latching) rung holding an output on after the start button is released — the first pattern every learner masters in a 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
Seal-in / latching — the start-stop pattern, scored against the exact test cases an interviewer would ask.
Browse all 170 scenarios →Start the guided lessons →How the simulator works →

What you can practice

Scored scenarios — where PLC-Fiddle stops

The PLC scan cycle — read inputs, execute logic, update outputs — the loop our built-in simulator runs against your code to auto-grade each scenarioThe repeating PLC scan cycle: read inputs, execute the ladder logic, update outputs, then housekeeping, looping continuously.1Read Inputs2Execute Logic3Update Outputs4HousekeepingSCANCYCLE
Every scenario runs the real read-solve-write scan cycle — the same execution model behind PLC-Fiddle's fiddle mode, wrapped around scored test cases.

Motor Start / Stop

Three-wire control with seal-in — the first scenario every electrician should pass.

View scenario →

Traffic Light

Pure sequencing with timers — the intuition you cannot skip.

View scenario →

Conveyor Sort

Sensors, pushers, and diverters — the scenario that separates real programmers from tinkerers.

View scenario →

PID Temperature

Closed-loop control with Kp/Ki/Kd tuning.

View scenario →

Elevator

Full state machine with up/down logic and floor requests.

View scenario →

Batch Mixer

Recipe-driven sequence with timer interlocks and alarm states.

View scenario →

Third options

Not the right fit? Look at these.

  • Factory IO if you want 3D factory visualization on a Windows machine — see our Factory IO alternative.
  • Codesys SoftPLC if you want the industry-reference desktop IEC IDE — see our Codesys alternative.
  • OpenPLC on Raspberry Pi if you want real hardware for under $100.
Questions

PLC-Fiddle alternative FAQ

PLC Fiddle (plcfiddle.com) is a free, no-signup browser-based ladder logic sandbox. You open a tab, drop contacts and coils onto rungs, and watch them execute. It became the go-to recommendation on r/PLC and MrPLC for anyone asking "where can I try ladder without installing anything?" because the friction is essentially zero. Its limits are that it is ladder-only, has no dialect switching (no Allen-Bradley or Siemens mode), and offers no scored feedback.

Ready for graded practice?

Start with three free scored scenarios. No credit card, no install, any browser.

Create free account →

Software evaluation field guide

PLC Fiddle alternative: evaluation checklist

Direct answer

The user can compare playgrounds by supported language, persistence, shareability, execution model, I/O, machine context, tests and learning feedback.

Written for learners seeking a quick browser editor for ladder or Structured Text with execution, I/O and observable machine practice.

System map / 02

NODE 01observable

Requirement

The need to draft, execute, share, test or connect PLC code to a modeled machine.

NODE 02observable

Test job

Editor language, runtime, I/O, saved projects, links, examples, grading, account and export boundaries.

NODE 03observable

Baseline result

One short logic example run from input stimulus to observable output.

NODE 04observable

Stress case

Unsupported instructions, time limits, browser storage, mobile use, privacy and account restrictions.

NODE 05observable

Failure handling

A parse, execution, save, share or behavior mismatch revealed by a reproducible snippet.

NODE 06observable

Decision record

The snippet retained with expected results and recreated in the intended target environment.