Ladder
Available nowDraw a rung. Press run. Watch it conduct.
A ladder editor with a real scan engine behind it. It is the canvas the AI writes onto, it opens on your own programs rather than an empty grid, and it works entirely in the browser with no account and no backend.
Open LadderIn short
Is there a free online ladder logic editor with a real PLC simulator?
LADX Ladder is a browser based ladder logic editor with a scan accurate simulator behind it. It models the output image, holds edge memory per instruction, and runs timers on elapsed milliseconds rather than scan counts, so a rung behaves the way it would on a controller. It needs no account, no licence and no installation.
The problem
Learning or checking ladder logic normally means owning a licence and a controller, or using a simulator that solves rungs like equations and quietly teaches you the wrong model of how a PLC behaves.
What it does
A real scan engine
An output image, so a coil written after a contact was solved does not reach it until the next sweep. Edge memory held per instruction, so a button held down counts once. Timers on elapsed milliseconds rather than on scan count.
Twenty-three instructions, the ones people actually use
XIC, XIO, OTE, OTL, OTU, ONS, TON, TOF, CTU, CTD, RES, the six comparisons, MOV and the four arithmetic blocks, and JSR to call another routine. Timer and counter members are addressable: .DN, .TT, .EN, .ACC, .PRE.
It opens on your work
Recent programs first, then four complete starter programs that run as they are: seal-in motor start, a ten-second conveyor, and two more. Each is copied on open, so taking one apart cannot spoil it for the next person.
Describe a rung and it writes one
The AI box takes plain language and returns rungs on the canvas, using the tags already in your tag table. It flags a seal-in leg missing its stop condition, which is the mistake generated ladder makes most often.
Tags with addresses, and a focus mode
Every tag gets a plausible address and a device type, so the simulator can show a panel with real switches and lamps. Full-screen when the rung is the only thing that matters.
What it doesn't do
Listed because you would find out anyway, and finding out later is worse.
- It is a teaching and verification simulator, not a certification tool. It does not replace commissioning.
- It never connects to a physical controller, by design, and that will not change.
- There is no retentive timer. TON and TOF only; an RTO has to be built from a counter or a latch.
- Ladder only. Structured Text is read and written by Convert but not drawn here.
Questions
- Is LADX Ladder free to use?
- Yes. The ladder editor and its simulator run entirely in the browser with no account, no licence and no server. Anything that uses a model needs a provider key you supply yourself, because LADX holds no shared inference key and does no metering.
- Does the simulator behave like a real PLC?
- It keeps an output image, so a coil written on rung twelve reaches rung thirteen in the same scan and rung four only on the next one. Edge memory is held per instruction, so a held button counts once. Timers count elapsed milliseconds, not scans. Most teaching simulators do none of these.
- Which instructions does it support?
- Twenty three: XIC, XIO, OTE, OTL, OTU, ONS, TON, TOF, CTU, CTD, RES, the six comparisons, MOV and the four arithmetic blocks, and JSR. Timer and counter members are addressable, so a contact can examine T1.DN and a bar can read T1.ACC.