CODESYS 4: The future-proof IEC 61131-3 IDE for you, your team, and your CI/CD pipeline
Same compiler, same runtime system, same libraries. New user interface.
Version 1.0.0.0 is available since September 24, 2026. CODESYS 4 is a second programming system alongside the CODESYS Development System 3. You continue to program according to IEC 61131-3, in Structured Text and in Ladder Diagram. What’s new is what lies beneath: The user interface runs in a browser window, the project is stored on the hard drive as a folder containing text files, and the command line is available alongside the user interface.
CODESYS 4 revamps the development environment while retaining the proven foundation. The compiler is the same as in CODESYS 3, the libraries are the same, and the runtime system on the controller remains unchanged. Code compiled by CODESYS 4 therefore runs on any controller that already executes code from CODESYS 3.
CODESYS 4 does not replace CODESYS 3. Both tools will continue to be developed and maintained in parallel. You decide for yourself if and when CODESYS 4 is right for your project. A combination is also possible—for example, developing in CODESYS 4 and commissioning in the CODESYS Development System 3.
The feature set of the first version is intentionally limited. Productive work is currently possible in two use cases:
- Library development in Structured Text and Ladder Logic with automated building (the “CI/CD” build process)
- Small device projects using Modbus TCP
What stays the same
Let's start with the most important point, since it answers the most common question: Your existing work and hardware will remain usable.
The compiler, libraries, and runtime are the same. CODESYS 4 uses the same CODESYS compiler as the CODESYS Development System 3 and the same libraries. The same runtime system runs on the controller. Your investments in hardware, libraries, and IEC 61131-3 expertise remain intact.
You continue to program according to IEC 61131-3. Structured text and ladder diagram (LD) are included from the very first version. The ladder diagram editor is the familiar graphical editor from CODESYS 3, redesigned for CODESYS 4. You don’t need to learn a high-level language to work with CODESYS 4.
Library projects are compatible in both directions. A library project stored in CODESYS 3 using file-based storage opens in CODESYS 4, and vice versa. A library compiled in CODESYS 4 (Compiled Library) can be integrated into projects in both environments.
Device projects require conversion. They cannot be opened directly between the two environments. A conversion tool is planned, but it is not yet included in version 1.0.0.0.
Both tools operate side by side. CODESYS 3 continues to be developed and maintained. It is backed by over 300,000 users and more than 20 years of proven reliability. There are no plans to discontinue it, and there is no set date for CODESYS 4 to fully replace it.
Your first 30 minutes
Install
Windows: Run the installer (.exe) for x64. Linux: Install the Debian package (.deb) for x64 or ARM64. On Windows, CODESYS 4 then launches in its own window; on Linux, a command opens the interface in the local browser.
Open sample project
The online help contains sample projects along with descriptions. Open one of them before creating your own project: This will show you the structure of a CODESYS 4 project using a completed example.
Create your own project
The step-by-step guide takes you from setting up the workspace to adding the controller and loading the application.
Connect the controller and monitor it
Select a CODESYS-based controller from the list below, load the application, and monitor your variables directly in the editor. The connection to the controller is established via the CODESYS Gateway, version 3.5 or later.
None of the above apply?
In that case, CODESYS 3 will remain your tool for productive work for now. Take a look at CODESYS 4 anyway: It’s free to use through the end of 2028, and you’ll get to know the concepts that form the foundation for future enhancements. And if you’re already professionally developing PLC applications in CODESYS 3 and using the additional tools included in the Professional Developer Edition – such as CODESYS Git or the CODESYS MCP Server – then CODESYS 4 is simply included as another professional tool in your license bundle. This means there will be no additional costs for you in the long term.
Building libraries: the process
Before we get started, here are two definitions:
Git version control is a repository where every change to your code is tracked, along with the time it was made and who made it.
A pipeline is a sequence of steps on a server that starts automatically when a specific event occurs. It compiles and checks your code without requiring you to open a program.
Develop
You write the library in the Structured Text editor, which features syntax highlighting, auto-completion, and tooltips when you hover the mouse over the code. Alternatively, you can continue developing in CODESYS 3 (see Scenario A below).
Save and compare
You check in the project directory to Git. Since all the files are text files, you can see exactly which line has been changed when you compare them. Merging parallel changes and conducting reviews as a team require the same tools that your IT department already uses.
Record dependencies
Libraries.json specifies which libraries you are using, including open version ranges such as “3.5.*.” Libraries.lock.json records the specific versions that were selected, along with a checksum for each library. Both files are located in the project. This ensures that a computer in the pipeline uses exactly the same library versions as your workstation.
Approve and let it build automatically
You mark the released version in the repository with a version number. This mark (tag) triggers the pipeline. The server retrieves the marked version and calls the c4 library `save-compiled`. The compilation runs without a user interface, so no one needs to be present to monitor it.
Deliver and integrate
The result is a compiled library (file extension .compiled-library) without accompanying source code. It can be signed, stored with a version number, and then integrated into projects in CODESYS 3 and CODESYS 4. The pipeline notifies you of success or errors via email or chat.
Small device projects: the process
Create a project
Create a workspace, create a device project, select a CODESYS Control SL runtime system (for example, CODESYS Control Win V3 x64), and specify the programming language.
Programming
The flow logic is created using Structured Text, interlocks, and links in the Ladder editor. The Ladder editor is currently available in version 0.1 with basic offline functions and will be further expanded.
Connecting inputs and outputs
In the project tree, add an Ethernet node, followed by the Modbus TCP client/server or the Modbus TCP server device. Create channels and map inputs and outputs to variables.
Load and observe
Load the application onto the controller; monitor variables directly in the editor or in the watchlist.
What's still missing here:
In version 1.0.0.0, it is not possible to make online changes to a running program, nor is it possible to set breakpoints and write or force variables. The display of signal flows in Ladder at runtime is also still not available. CODESYS 3 therefore remains the right tool for traditional commissioning on the machine.
What's new in version 1.0.0.0
Note on classification
"Web-based" describes the interface technology. CODESYS 4 is not a cloud service and is not offered as subscription software. You decide where the software runs. All four versions allow for operation entirely within your own network. Server and device operation require Linux.
What version 1.0.0.0 does not yet include
Development began with the foundation: file-based storage, separation of the user interface and background processes, command-line invocation, and an extension model. The feature set continues to grow with each version.
There are two distinct levels to consider here.
Outside of these two use cases, CODESYS 3 remains your tool. This applies to everything beyond Structured Text, Ladder Diagram, and Modbus TCP—such as the other IEC 61131-3 languages, additional fieldbuses, visualization, motion, and safety.
Even within these two use cases, there are still features missing that you are familiar with from CODESYS 3. These include online functions for the running controller (online changes, breakpoints, forcing variables), convenience features for editing (including refactoring, cross-reference lists, and project-wide undo and redo), quality assurance tools (including Test Manager, static analysis, automated module tests, and library documentation generation), as well as extensions from external partners with their own editors and configurators. These missing features are known and are being addressed step by step.
The specific features included in each version are listed in the release notes and in the online help for that version. The semi-annual CODESYS Feature Briefing provides an outlook for the next six to twelve months.
Supported controllers
In version 1.0.0.0, only CODESYS Control SL runtime systems are supported.
Platform | CODESYS Runtime System |
Raspberry Pi | CODESYS Control for Raspberry Pi MC SL, CODESYS Control for Raspberry Pi SL, CODESYS Control for Raspberry Pi 64 SL |
Windows Soft PLC | CODESYS Control Win V3, CODESYS Control Win V3 x64, CODESYS Control RTE V3, CODESYS Control RTE V3 x64 |
Linux | CODESYS Control for Linux ARM SL, CODESYS Control for Linux ARM64 SL, CODESYS Control for Linux SL |
Virtual Controller | CODESYS Virtual Control for Linux ARM SL, CODESYS Virtual Control for Linux ARM64 SL, CODESYS Virtual Control for Linux SL |
Minimum version of the runtime system
CODESYS V3.5 SP19 or later.
Reason: Starting with this version, the runtime system includes user management. The insecure protocols from older versions were not reimplemented in CODESYS 4. The connection to the PLC is established via the CODESYS Gateway starting with version 3.5.
Control systems that were previously programmed using CODESYS 3
Can CODESYS 4 be used with any controller running a sufficiently up-to-date CODESYS runtime system?
The answer has two parts. At the compiler and runtime system level, there are no obstacles: Compiled code from CODESYS 4 runs on any controller that also executes code from CODESYS 3, provided that the runtime system is based on at least Service Pack 19.
However, only the CODESYS Control SL runtime systems listed above are approved for project engineering in version 1.0.0.0. The reason lies not in the runtime system, but in the project configuration part: A device comes with a device description and, if applicable, manufacturer-specific libraries. Resolving these libraries and their placeholders in CODESYS 4 may cause problems unless the device manufacturer has tested them for CODESYS 4. Technically, hardware from other manufacturers can be integrated, but there is currently no guarantee of functionality.
The recommended approach: The device manufacturer tests the device description and libraries with CODESYS 4 and, if necessary, makes them available as a CODESYS 4 Content Extension. Users will likely be able to install such extensions starting with version 1.1.0.0. Please contact your device manufacturer if you wish to use CODESYS 4 with their hardware.
Watch CODESYS 4 in action
Video: Motivation and background (webinar, part 1)
Why a web-based development environment for PLCs is being created and how it compares to CODESYS 3.
Video: Live showcase on library development (webinar, part 2)
The presentation will cover a textual comparison of two project versions on the Git server, logging in to the shared server, the editors, and a GitLab pipeline leading up to the downloadable translated library.
How to get
Purchase and download
CODESYS 4, Version 1.0.0.0, available in the CODESYS Store.
Distribution formats
- Windows x64: Installer (.exe)
- Linux x64: Debian package (.deb)
- Linux ARM64: Debian package (.deb)
License and costs
Use of CODESYS 4 is free of charge until the end of 2028. A paid licensing model is planned for 2029 at the earliest and will be part of the Professional Developer Edition. Anyone who already develops applications using the additional tools in the Professional Developer Edition—such as CODESYS Git or the CODESYS MCP Server—will receive CODESYS 4 as an additional tool in the same package at no extra cost. The CODESYS Development System (V3) remains free of charge. In the first version, no separate license is required for the computer used in a build pipeline.
System requirements
- Operating system: Windows x64, Linux x64, or Linux ARM64. Server and device operation require Linux.
- Browser for operation under Linux and in server mode: a current browser
- Controller: CODESYS runtime system, Service Pack 18 or later; see list above
- Connection to the controller via CODESYS Gateway, version 3.5 or later
- An Internet connection is not required for operation
Stay up to date
Registration for the Early Adopter program
Participants will receive in-depth information about CODESYS 4 and will have the opportunity to provide feedback on prioritization. The program is open to anyone interested and does not include early access to the software.