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Introduction

@dineug/erd-editor-mcp is an MCP server that lets a coding agent edit erd-editor diagrams. Claude Code, Codex, and any other client of the Model Context Protocol get one tool per operation on a document: add a table, rename a column, relate two tables, import a DDL dump, read the schema back as SQL.

When the document is open in the VS Code extension, the agent joins the editor like a collaborator. Each change shows up on the canvas as it happens and stays unsaved until the agent or you save, and the agent's undo reverts only its own edits. With no VS Code window on the document, the same tools edit the file itself.

A coding agent adding tables and relationships to a diagram open in VS Code

What an Agent Can Do​

  • Build or change a schema in conversation: tables, columns and every column option, relationships, indexes, memos, colors, and positions on the canvas.
  • Replace the document with a schema parsed from SQL DDL, GraphQL SDL, DBML, or AML, or with another .erd.json document.
  • Read the diagram back as a list of ids, as whole entities, as DDL for any of the eight databases, or as the raw JSON. On a schema of thousands of tables it reads a page or a few tables at a time. See Reading a Document.
  • Change the settings the document stores: the database, the Code Generator language and name cases, the bracket type, and which parts of a table are shown.
  • Run several edits as one, all or none, which one undo reverts. See erd_batch.
  • Undo and redo its own edits, never yours.

What it does not do:

  • Zoom, scroll, or switch tabs. Those belong to each viewer, not to the document, so no tool changes them.
  • Run the Code Generator. erd_read answers DDL or JSON, and the agent writes code from that itself.
  • Edit live in IntelliJ. The IntelliJ plugin keeps no lock file for the server to find, so a document open there counts as closed and the agent edits the file on disk. The plugin reads the file only when it opens it, and your next edit there writes the whole diagram back over the agent's changes, so close the diagram in IntelliJ while an agent edits it.

How It Works​

The server is a stdio process your MCP client starts. For every call it looks for a VS Code window that holds the document:

  • Live — a window has the document in its workspace or open. The server joins that window's editing session and the edit lands in the editor, unsaved.
  • Headless — no window. The server loads the file, applies the edit, and writes the file back.
  • Refused — a window holds the document but has its hub off. The server reads from disk but writes nothing, since the open editor would overwrite the file on its next save.

See Live and Headless for the details.

Requirements​

Node.js22.12 or later, to run the server
An MCP clientClaude Code, Codex, or any client that can start a stdio server
VS Code, for live editing1.101.0 or later, with the ERD Editor extension 3.0.0 or later

Next: Install.