Documentation

Last updated: March 2026

This reference covers everything you need to use Diagram2Code effectively: the input syntax for Mermaid and PlantUML diagrams, the SQL DDL output format for each supported database dialect, ORM model generation, directive syntax for fine-tuning the output, and the REST API for programmatic use. Use the navigation on the left or the section cards below to find what you need.

How It Works

The pipeline has three stages:

1. Parse — The diagram text (Mermaid or PlantUML) is lexed and parsed into an Intermediate Schema Model (tables, columns, relationships).
2. Normalize — The schema is cleaned: tables without a primary key get a synthetic id column, duplicate columns are removed, and warnings are emitted.
3. Generate — The normalized schema is emitted as SQL DDL for the chosen database dialect, with dialect-specific type mapping, quoting, constraints, and comments.

Quick Start Example

Here's a simple diagram and the SQL it generates for each database:

erDiagram
    USER {
        int id PK
        string name
        string email
    }
    ORDER {
        int id PK
        int user_id FK
        decimal total
    }
    USER ||--o{ ORDER : places

CREATE TABLE "user" (
    "id" SERIAL PRIMARY KEY,
    "name" TEXT,
    "email" TEXT
);

CREATE TABLE "order" (
    "id" SERIAL PRIMARY KEY,
    "user_id" INTEGER,
    "total" NUMERIC
);

ALTER TABLE "order"
    ADD CONSTRAINT "fk_order_user_id"
    FOREIGN KEY ("user_id") REFERENCES "user"("id");

Documentation Sections

The full reference is split into focused pages: