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.

Start freeTry motor start/stop →

Join 1300+ learners practicing PLC programming

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 practise 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 scenariosNo40 auto-graded
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 40 scenarios →Start the guided lessons →How the simulator works →

What you can practise

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 visualisation 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 →