Diagram to Code — Free ER Diagram Converter

Convert Mermaid & PlantUML ER diagrams to SQL & ORM models — instantly.

Mermaid ER PlantUML PostgreSQL MySQL SQLite Oracle GORM REST API
mermaid
Live preview mermaid

New to Diagram2Code?

Learn how to write ER diagrams and get the most out of the converter.

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Documentation Overview Start here — features, how it works, quick start
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Mermaid ER Syntax Tables, columns, PK/FK markers, relationships
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PlantUML Syntax Entities, stereotypes, key differences from Mermaid
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REST API Convert diagrams programmatically via HTTP

What is Diagram2Code?

Diagram2Code is a free online diagram to code converter that turns Mermaid ER diagrams and PlantUML entity-relationship diagrams into production-ready SQL DDL statements and ORM model code. Paste your diagram, choose your target output, and get instant code. Also known as a diagram 2 code tool, it eliminates the need to hand-write SQL schemas from your ER designs.

Supported Databases

  • PostgreSQL — SERIAL primary keys, CREATE TYPE enums, COMMENT ON syntax
  • MySQL — AUTO_INCREMENT, inline ENUM, backtick quoting
  • SQLite — Type affinity mapping, IF NOT EXISTS support
  • Oracle 19c+ — IDENTITY columns, NUMBER types, VARCHAR2, COMMENT ON

Supported ORM Frameworks

  • GORM (Go) — Free tier, generates Go structs with GORM tags
  • SQLAlchemy (Python) — Declarative base models with relationship fields
  • TypeORM (TypeScript) — Decorator-based entity classes
  • Prisma (TypeScript) — Prisma schema with datasource and client blocks
  • JPA / Hibernate (Java) — Jakarta Persistence entity classes with annotations
  • Django ORM (Python) — Django model classes with Meta and migration stubs
  • Sequelize (JavaScript) — Sequelize model definitions with associations
  • Entity Framework Core (C#) — EF Core entities with DbContext

How It Works

The tool parses your diagram into an intermediate schema model, normalizes it (adding synthetic primary keys, deduplicating columns), then generates dialect-specific SQL or framework-specific ORM code with proper type mapping, constraints, foreign keys, and relationships. Read the full documentation for details.

Common Use Cases

Developers use Diagram2Code at every stage of a project lifecycle:

  • New project bootstrap — Design the data model visually, generate your initial migration script in seconds, and import it into your database. No boilerplate to write.
  • Schema reviews — Share a Mermaid diagram in a pull request description. Reviewers can see the data model at a glance without reading raw SQL.
  • ORM synchronization — After changing the diagram, regenerate your GORM structs or Django models so your application code stays in sync with the schema.
  • Documentation — Embed live Mermaid diagrams in Markdown README files or wikis. The diagram is both human-readable documentation and the executable source of truth.
  • Learning SQL DDL — Students and developers learning database design can use the converter as a teaching tool: draw a diagram, inspect the generated SQL, and understand how ER concepts map to real DDL syntax.
  • CI/CD pipelines — Use the REST API or CLI to regenerate schema files automatically on every commit, catching schema drift before it reaches production.

Frequently Asked Questions

What is a diagram to code converter?
A diagram to code converter is a tool that reads a text-based diagram — such as a Mermaid ER diagram or PlantUML entity diagram — and automatically generates production-ready source code. Diagram2Code converts your ER diagram directly to SQL DDL and ORM model code, eliminating hand-written boilerplate.
How do I convert a diagram to code?
Paste your Mermaid ER or PlantUML diagram into the input field above, select your target database or ORM framework, and click Convert. The diagram 2 code generator instantly produces SQL DDL statements or ORM model classes ready for use in your project.
What diagram formats are supported?
Diagram2Code supports Mermaid erDiagram syntax and PlantUML entity-relationship syntax. Both formats can be converted to SQL or ORM code for PostgreSQL, MySQL, SQLite, Oracle, and eight ORM frameworks.
Is the diagram to code tool free?
Yes. SQL DDL generation for all four databases (PostgreSQL, MySQL, SQLite, Oracle) is completely free with no sign-up required. GORM model generation is also free. Advanced ORM frameworks require a Developer tier subscription. See the Pricing page for full details.
What is "diagram 2 code"?
"Diagram 2 code" (or "diagram to code") refers to generating source code automatically from a diagram, rather than writing it by hand. Diagram2Code does exactly this: it turns your database ER diagram into correct, production-ready SQL and ORM code in seconds.
Does Diagram2Code store my diagrams?
No. Your diagram text is sent to the server only for the duration of the conversion request. It is never stored, logged, or retained in any database. Your schema data remains private. See the Privacy Policy for full details.
Can I use the generated SQL commercially?
Yes, absolutely. All code generated by Diagram2Code belongs to you and may be used in personal or commercial projects without restriction or attribution.
Is there a REST API I can use in my CI/CD pipeline?
Yes. The same conversion engine is available as a documented REST API at /v1/convert/sql and /v1/convert/orm. Anonymous API access is available for up to 100 calls per month. Developer tier subscribers get a personal API key and 5,000 monthly calls. See the API Reference.
How do I report a bug or request a feature?
Open an issue on our GitHub repository. We aim to respond to bug reports within 2–3 business days. You can also reach us via the Contact page.
What SQL features are supported in the generated output?
Diagram2Code generates CREATE TABLE statements with primary keys (SERIAL / IDENTITY / AUTO_INCREMENT depending on dialect), foreign key constraints with ON DELETE / ON UPDATE actions, NOT NULL constraints, DEFAULT values, unique constraints, and indexes. Column type mapping is dialect-specific — for example, PostgreSQL uses TIMESTAMPTZ and JSONB, while MySQL uses DATETIME and JSON. Enum types, column comments, and composite primary keys are also supported. See the SQL DDL Generation docs for the full feature matrix.