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
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?"
Background
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
No signup. No install. Open a tab, drop rungs, watch them run. The lightest possible way to try ladder.
Every circuit gets a URL. Pasting your 4-rung attempt into a forum post for help is a one-click action.
Absolute beginners are not drowned in menus. The contact-coil-timer mental model is the whole tool.
Where you outgrow it
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.
Generic ladder only. There is no way to practise Allen-Bradley tag-style or Siemens #Tag conventions — the two dialects that dominate job postings.
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 account, no saved scenario history, no PDF export of completed work. Interview-ready evidence lives in screenshots, not a clean portfolio.
You cannot simulate the 30-minute-per-question pressure that Rockwell and Siemens engineering interviews use.
Updates have been rare in recent years. If you hit a bug or want a new feature, the path forward is unclear.
Feature comparison
| Feature | PLC-Fiddle | Ours |
|---|---|---|
| Platform | Any browser | Any browser |
| Signup required | No | Free tier — optional; Pro — yes |
| Languages | Ladder only | Ladder, ST, FBD, SFC |
| Dialects | Generic | IEC 61131-3, Allen-Bradley, Siemens |
| Scored scenarios | No | 40 auto-graded |
| Progress tracking | URL-based only | Account-based with history |
| Interview timer | No | Yes (Pro) |
| PDF portfolio export | No | Yes (Pro) |
| Development pace | Dormant-ish | Active weekly updates |
| Price | Free forever | Free tier + Pro subscription |
What you can practise
Three-wire control with seal-in — the first scenario every electrician should pass.
View scenario →Sensors, pushers, and diverters — the scenario that separates real programmers from tinkerers.
View scenario →Third options
Start with three free scored scenarios. No credit card, no install, any browser.
Create free account →