Documentation

Diagram2Code converts Mermaid ER diagrams and PlantUML entity-relationship diagrams into production-ready SQL DDL and ORM model code. This documentation covers everything from a 2-minute quick start to the full API reference.

Quick Start

No account required. Paste your diagram, select a target, and click Convert.

Input — Mermaid ER diagram

erDiagram
    USER {
        int id PK
        string email UK
        string name
    }
    POST {
        int id PK
        int user_id FK
        string title
        text body
    }
    USER ||--o{ POST : writes

Output — PostgreSQL DDL

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

CREATE TABLE "post" (
    "id"      SERIAL PRIMARY KEY,
    "user_id" INTEGER,
    "title"   TEXT,
    "body"    TEXT
);

ALTER TABLE "post"
    ADD CONSTRAINT "fk_post_user_id"
    FOREIGN KEY ("user_id")
    REFERENCES "user"("id");

⚡ Open the Converter

Try it now — no sign-up, no install

🔀 Schema Diff

Compare two diagram versions, see what changed

How It Works

The conversion pipeline has three stages:

Parse — The diagram text is parsed into an intermediate Schema model (tables, columns, relationships, constraints).
Normalize & Validate — Synthetic primary keys are added where missing, column names are deduplicated, and foreign-key targets are validated.
Generate — The Schema model is rendered into dialect-specific SQL or framework-specific ORM code using type mapping tables and configurable templates.

Because all parsers produce the same intermediate Schema, a Mermaid diagram and a PlantUML diagram with identical structure will produce identical SQL output.

Supported Input Formats

🧜 Mermaid ER

erDiagram syntax. Supports PK/FK/UK markers, %% directives for NOT NULL, DEFAULT, CHECK, CASCADE, composite indexes, enums, and more.

🌱 PlantUML

@startuml entity syntax. Supports * mandatory prefix, <<PK>> stereotypes, ' comment directives for advanced metadata.

Supported SQL Dialects

Dialect	Auto-increment	Enums	Column comments	Table comments
PostgreSQL	`SERIAL`	`CREATE TYPE … AS ENUM`	`COMMENT ON COLUMN`	`COMMENT ON TABLE`
MySQL	`AUTO_INCREMENT`	Inline `ENUM(…)`	Inline `COMMENT 'text'`	Table option `COMMENT='text'`
SQLite	`INTEGER PRIMARY KEY`	Stored as `TEXT` with CHECK	—	—
Oracle 19c+	`GENERATED ALWAYS AS IDENTITY`	Stored as `VARCHAR2` with CHECK	`COMMENT ON COLUMN`	`COMMENT ON TABLE`

Supported ORM Frameworks

Framework	Language	Tier
GORM	Go	Free
SQLAlchemy	Python	Developer+
TypeORM	TypeScript	Developer+
Prisma	TypeScript	Developer+
JPA / Hibernate	Java	Developer+
Django ORM	Python	Developer+
Sequelize	JavaScript	Developer+
Entity Framework Core	C#	Developer+

Navigation

Use the sidebar on the left (or the menu above on mobile) to navigate the documentation sections:

Mermaid ER Syntax — full syntax reference including %% directives
PlantUML Syntax — entity syntax, stereotypes, and ' directives
SQL DDL Generation — type mapping, constraints, dialect differences
ORM Generation — per-framework examples and field mapping
Schema Diff — comparing two diagram versions
API Reference — REST endpoints, request/response shapes, authentication