Introduction

Define your types once. Generate code and diagrams everywhere.

typeDiagram is a tiny, language-neutral DSL for describing algebraic data types — records, tagged unions, generics, aliases. From one .td file, you get:

• Source code in TypeScript, Python, Rust, Go, C#, F#, Dart, PHP, and Protobuf — DTOs, data classes, discriminated unions, pattern-matchable enums — generated from the same definition, always in sync.
• SVG diagrams with automatic orthogonal layout — no dragging, no fiddling, versionable in git.
• Round-trip conversion from existing TypeScript/Python/Rust/Go/C#/F#/Dart/PHP/Protobuf back to the DSL, so you can retrofit an existing codebase.

This is not a diagramming tool dressed up with a text input like Mermaid or PlantUML. typeDiagram is a shared schema for your data model — the diagram is a side effect, not the goal. The primary output is code, in as many languages as you need, kept strictly in sync by construction.

Why this matters

When your backend is Python, your mobile app is Dart/Kotlin, your web client is TypeScript, your data pipeline is Rust, and your gRPC services speak Protobuf, keeping DTOs aligned across nine languages is a full-time job. typeDiagram inverts the problem: one definition, N outputs. Change a field, regenerate, done. Every consumer of the schema stays honest because they all build from the same source.