MCP Server

erdn-lang ships a built-in Model Context Protocol (MCP) server so AI assistants and MCP-compatible editors can convert SQL schemas to ERDN and generate diagrams — no GUI, no clipboard, no copy-paste.

Installation

Install the MCP server binary with go install:

go install github.com/headercat/erdn-lang/cmd/erdn-mcp@latest

You need Go 1.21 or later. The binary is placed in $GOPATH/bin (usually $HOME/go/bin). Make sure that directory is on your PATH.

Client Configuration

Using the installed binary

Add the following to your MCP client's configuration file (e.g. claude_desktop_config.json, .cursor/mcp.json, or VS Code's settings.json):

{
  "mcpServers": {
    "erdn-lang": {
      "type": "stdio",
      "command": "erdn-mcp"
    }
  }
}

Without installing (run directly from the module proxy)

If you prefer not to install a binary, you can run the server on demand via go run. No local clone is needed — Go fetches the package automatically:

{
  "mcpServers": {
    "erdn-lang": {
      "type": "stdio",
      "command": "go",
      "args": ["run", "github.com/headercat/erdn-lang/cmd/erdn-mcp@latest"]
    }
  }
}

Auto-discovery

The repository root contains a ready-to-use .mcp.json file. MCP clients that support auto-discovery (such as recent versions of Claude Desktop and Cursor) will pick it up automatically when you open the repository folder.

Available Tools

convert_sql_to_erdn

Converts SQL CREATE TABLE and FOREIGN KEY statements into ERDN source text.

Input

Parameter	Type	Description
sql	string	One or more SQL DDL statements

Output — The equivalent .erdn schema as a string.

Example prompt

Convert this SQL schema to ERDN:

CREATE TABLE users (id BIGINT PRIMARY KEY, username VARCHAR(64) NOT NULL);
CREATE TABLE posts (id BIGINT PRIMARY KEY, author_id BIGINT, FOREIGN KEY (author_id) REFERENCES users(id));

---

generate_svg_from_erdn

Validates ERDN source and returns the rendered SVG diagram as a string.

Input

Parameter	Type	Description
erdn	string	ERDN schema source

Output — A self-contained SVG string that can be saved to a file or embedded in HTML.

Example prompt

Generate an SVG diagram for this ERDN schema:

table users (
  id       bigint primary-key auto-increment
  username varchar(64) not-null indexed
)

Running the Server Manually

If you have a local clone of the repository you can also launch the server directly:

go run ./cmd/erdn-mcp

The server communicates over stdio using JSON-RPC 2.0, which is the standard MCP transport.