IECode – Structured Text for TwinCAT

Edit TwinCAT 3 .TcPOU, .TcDUT, .TcGVL and .TcIO files as plain Structured Text in VS Code, browse and extend PLC projects, work with several libraries and applications in one workspace, and build / deploy through the iecode CLI.

No export/import, no .st files on disk. The TwinCAT XML file stays the only source of truth; VS Code shows a live text view of it and saving writes your text back into the XML file.

FB_Motor.TcPOU (XML on disk)                 Editor (iecode:/…/FB_Motor.TcPOU)
───────────────────────────────              ─────────────────────────────────
<POU Name="FB_Motor" Id="{…}">               FUNCTION_BLOCK FB_Motor
  <Declaration><![CDATA[…]]>       ⇄         VAR_INPUT … END_VAR
  <Implementation><ST><![CDATA[…]]>          //---- IMPLEMENTATION ----
  <Method Name="Start" Id="{…}">             IF bEnable THEN …
    …                                        //==== METHOD Start ====
  <LineIds …>                                METHOD PUBLIC Start : BOOL …

Features

Settings

How it works

• A FileSystemProvider for the iecode: scheme. readFile decodes the XML into one ST document, and writeFile reads the current XML from disk and splices only the CDATA blocks that changed.
• A save with no changes leaves the file byte-identical. GUIDs, FolderPath, attributes, CRLF line endings, BOM and non-ST bodies (CFC/LD/SFC, shown as read-only markers) are all kept.
• If you change a method's code, the extension removes its <LineIds> entry, which is stale at that point; TwinCAT rebuilds it.
• Adding a //==== METHOD X ==== section creates a new <Method> with a fresh GUID, and deleting one removes it.
• Invalid views (e.g. a GET without a PROPERTY) are refused at save time with a line number. The editor stays dirty and the file isn't touched.
• When TwinCAT XAE changes the file on disk, the view reloads.

The ST view is also available on the command line (node out/src/cli.js, installed as iecode-st):

iecode-st decode <file>                                  # ST view
iecode-st diff <a.TcPOU> <b.TcPOU>                       # unified diff of the ST views
iecode-st diff --rev HEAD~3 [--to <ref>] <file>          # ST diff against git history
iecode-st links <x.tsproj> [--csv]                       # IO links
iecode-st links-diff --rev <ref> [--to <ref>] <x.tsproj> # IO link changes

As a git textconv for readable diffs (or use IECode: Show ST in git diff):

git config diff.iecode.textconv "node /path/to/out/src/cli.js decode"
echo "*.TcPOU diff=iecode" >> .gitattributes

Develop

npm install && npm test          # unit tests (view round trip, project model, templates, workspace, language, libraries)
./scripts/e2e.sh                 # end-to-end in real VS Code (throwaway profile)
npm run package                  # iecode-<version>.vsix

Or open this folder in VS Code and press F5.

Known limits

• Section order in the text doesn't reorder XML elements. A renamed section header counts as delete + add, so the member gets a new GUID.
• Renaming an object in the tree renames the file, its declaration and the .plcproj entry, but not references to it in other objects (use Rename Symbol for variables and members).
• Name resolution covers locals, members, EXTENDS, qualified names, arrays, pointers, GVLs and enums of the workspace; symbols from installed libraries (e.g. Tc2_Standard) are not known yet.
• Compiler messages are mapped to the ST view by object name; for errors in declarations the line may be off.
• The CLI-driven features have not been tested against a real TwinCAT installation yet.

Market check (Oct 2026)

Nothing on the market currently edits TcPOU XML in place as plain text without a conversion step.

License and trademarks

Apache License 2.0, see LICENSE and NOTICE.

TwinCAT®, Beckhoff® and EtherCAT® are registered trademarks of Beckhoff Automation GmbH. This extension is not affiliated with, endorsed by, or supported by Beckhoff Automation GmbH.