GUIDES
Rung Coder vs. the official CODESYS MCP Server
Both connect MCP-capable AI clients such as Claude, Codex or Cursor to the CODESYS Development System. They differ in how much of the engineering workflow they cover, which CODESYS versions they need and how they are licensed. This comparison is based on the official CODESYS documentation as checked on 2 November 2026.
The short answer
The CODESYS Development System MCP Server is the vendor's own add-on. According to its documentation it lets an AI read, write and edit Structured Text, browse the project, manage libraries and fetch their documentation, and check for compile errors. It needs CODESYS V3.5 SP22 or later and is licensed through the CODESYS Professional Developer Edition.
Rung Coder covers the same coding loop and continues past it: Ladder Diagram as well as ST, visualization pages, download to the controller, online debugging with live variables and a built-in version history. It runs on CODESYS V3.5 SP18 or newer and has its own subscription.
Side-by-side comparison
| CODESYS Development System MCP Server | Rung Coder | |
|---|---|---|
| Made by | CODESYS Group | Rung Coder |
| CODESYS version | V3.5 SP22 or later | V3.5 SP18 or later (SP21 and SP22 fully verified on real hardware) |
| Licensing | Part of the CODESYS Professional Developer Edition bundle | Own subscription, USD 9 per month, 2 months free |
| Installation | Add-on through the CODESYS Installer | Windows desktop app; you sign in, start CODESYS from it and paste one generated prompt into your AI client |
| AI clients | MCP-compatible clients over local stdio | MCP clients, plus CLI and Gateway modes |
| Structured Text | Read, write and edit | Read, write and edit |
| Graphical languages | Read only; cannot create or modify | Ladder Diagram: create POUs with real rungs and edit single rungs. Other graphical languages: create objects and declarations |
| Compile errors | Checks for compile errors and warnings | Compiles in the real IDE and loops until the build is clean |
| Visualization (HMI) | Not listed in the documentation | Creates whole pages: 11 element types, variable bindings, layout and an overlap check (SP20 or later) |
| Download and online | Not listed in the documentation | Login, download, online change, write and force variables, watch, 1 ms sampling, trace |
| Version control | Documentation recommends a separate Git setup | Built in: baseline before the first change, checkpoints, branches, diffs, rollback, optional remote Git |
| Approvals | Rights of the user logged into the IDE apply | Three permission levels; in Authorized mode the AI asks for full control (needed for every online action) and waits for your confirmation |
Where the official MCP Server fits well
- You already license the CODESYS Professional Developer Edition and work on SP22 or later.
- You mainly want help writing, explaining and fixing Structured Text inside the IDE.
- You prefer a tool from the IDE vendor itself. CODESYS also researches local language models with Intel OpenVINO for teams that cannot use cloud AI.
Where Rung Coder goes further
- The loop ends on the controller, not in the editor: once you grant full control, the AI downloads, starts the application and samples live variables to check the behaviour.
- HMI pages are generated together with the logic, including variable bindings.
- Ladder Diagram is writable, which matters for plants and teams that standardise on LD.
- Every change is recoverable without setting up Git: a baseline is saved before the first AI change, and any checkpoint can be restored.
- It works on CODESYS V3.5 SP18 to SP21 projects that cannot move to SP22 yet.
Which one should you choose?
If ST assistance inside a recent IDE is what you need and the Professional Developer Edition is already in place, start with the official MCP Server. If you want the AI to deliver a running, verified project, including visualization, Ladder Diagram, online debugging and rollback, or you are on an older service pack, Rung Coder covers more of the work.
Rung Coder is free for 2 months, so you can try it on a copy of a real project. The AI for CODESYS guide explains the workflow and the requirements.
Sources
Try it on your own CODESYS project
Rung Coder is free for 2 months from your first sign-in, with no payment method needed. Windows 10/11 and CODESYS V3.5 SP18 or newer.