Melsec GX Import — VS Code Extension

Bidirectional bridge between VS Code and Mitsubishi GX Works3 — import PLC programs from GX Works3 to local files, edit them with full VS Code + Copilot power, and export changes back. Built on the GX Works3 Open Interface (GXW3OpenIF).

If this extension helps your Melsec GX Works3 workflow, you can support ongoing development with a voluntary PayPal donation.

Key Features

Import from GX Works3 (GX Works3 → local files)

Export to GX Works3 (local files → GX Works3)

Build and Diagnostics

Copilot / AI Agent Integration

The extension exposes Language Model Tools (prefix melsec_*) plus a @melsec chat participant:

• Connection / discovery — melsec_connect, melsec_disconnect, melsec_save_project, melsec_refresh
• Pull from GX Works3 → workspace — melsec_list_objects, melsec_import_object, melsec_import_project
• Push workspace → GX Works3 — melsec_export_file
• Build loop — melsec_build, melsec_rebuild

Exports that overwrite existing GX Works3 objects show a confirmation dialog unless melsecImport.lmTools.autoConfirmExports is enabled.

External CLI Bridge

External scripts can drive the same workflows through a localhost-only JSON bridge. The bridge is opt-in (melsecImport.cli.enabled). When enabled, the extension writes .melsec/cli.json with host, port and bearer token.

npm run melsec:cli -- current_project --pretty
npm run melsec:cli -- open_project --filePath "C:\Projects\MyPlc.gx3" --pretty
npm run melsec:cli -- import_object --objectName MyBlock --objectType pou --pretty

Requirements

GX Works3 Open Interface (GXW3OpenIF)

The extension requires the GX Works3 Open Interface (GXW3OpenIF) component from Mitsubishi Electric. Without it the extension cannot communicate with GX Works3.

• Make sure GXW3OpenIF is selected when installing GX Works3. It may be offered as an optional component in the GX Works3 installer.
• The OpenIF DLLs must be present in your GX Works3 installation directory, e.g.:
  • C:\Program Files\MELSOFT\GX Works3\GXW3OpenIF32.dll
  • C:\Program Files\MELSOFT\GX Works3\GXW3OpenIF64.dll
• If the DLLs are missing, reinstall GX Works3 and enable the GX Works3 Open Interface option.

Installation

1. Install the extension from the VSIX or build from source.
2. Make sure GX Works3 is installed.
3. Open a workspace folder in VS Code.
4. Run Melsec Import: Prepare Workspace to scaffold MelsecImport/, .github/, AGENTS.md, CLAUDE.md and .gitignore.
5. Optionally adjust settings via File → Preferences → Settings → Melsec GX Works3 Import.

Usage

Preparing the Workspace

Before importing for the first time, prepare the workspace so the extension can create the expected folder structure and AI assistant templates:

1. Open VS Code in a workspace folder.
2. Click the Melsec icon in the Activity Bar.
3. Click Prepare Workspace (folder icon) in the Connection view title bar, or run Melsec Import: Prepare Workspace.

The command creates:

<Workspace>/
├── .gitignore                        # Melsec-specific ignores
├── AGENTS.md                         # Open agents.md standard instructions
├── CLAUDE.md                         # Claude Code instructions
├── .github/
│   ├── copilot-instructions.md       # AI coding rules for GX Works3 XML files
│   ├── CLI-instruction.md            # CLI bridge usage for agents/scripts
│   └── ProjectDescription.md         # Living project architecture document
├── Tools/                            # Your automation scripts (with examples)
├── UserFiles/                        # Output dir for scripts (git-ignored)
└── MelsecImport/
    ├── .melsec-cache/                # Temporary cache (git-ignored)
    └── Projects/                     # Imported GX Works3 projects

Template files are only created if they do not already exist — existing files are never overwritten.

Connecting to GX Works3

1. Open VS Code in a workspace folder.
2. Click the Melsec icon in the Activity Bar.
3. Click Open Project or run Melsec Import: Open Project.
4. Select a .gx3 project file.

If GX Works3 is already running with the project open, you can also use Attach to Open Project (Melsec Import: Attach to Open Project).

Importing from GX Works3

1. Connect to GX Works3.
2. Browse the project structure in the Melsec Project Explorer sidebar.
3. Right-click on any node to import POUs, Global Labels or SDTs.
4. Files are saved under MelsecImport/Projects/<ProjectName>/ in your workspace.

Exporting to GX Works3

1. Connect to GX Works3.
2. In the VS Code Explorer, right-click an XML file or folder.
3. Choose Export to GX Works or Export All Objects to GX Works.
4. Objects are exported into the open project.

Architecture

VS Code Extension (TypeScript)
    ↓ electron-edge-js / edge-js
MelsecOpenIFBridge (.NET Framework 4.8)
    ↓ GXW3OpenIF32/64.dll
GX Works3 Open Interface
    ↓ GX Works3 IDE / PLC

Third-Party Licensing & Redistribution

• This extension code is released under MIT.
• Third-party notices for npm/NuGet components are listed in THIRD_PARTY_NOTICES.md.
• For Mitsubishi Electric GX Works3 Open Interface components, use and distribution are subject to Mitsubishi Electric package terms; evaluate those terms for your release scenario.
• Do not bundle or redistribute GXW3OpenIF32.dll, GXW3OpenIF64.dll, or other GX Works3 Open Interface binaries with this extension unless explicitly allowed by Mitsubishi Electric terms.
• End users must provide their own licensed GX Works3 installation and GXW3OpenIF entitlement.

Disclaimer of Liability

The extension is a development and automation tool, and all imports/exports modify engineering data at your own risk.

The author is not liable for any direct or indirect damages, production downtime, data loss, project corruption, safety incidents, or other consequences resulting from changes made to GX Works3 projects using this extension.

Users are fully responsible for validating, testing, and approving all generated or imported changes before deployment to real machines, production lines, or safety-related systems.

License

MIT — Copyright (c) 2026 Mariusz Czyrnek