What is a UML Diagram Generator?

A UML (Unified Modelling Language) diagram generator lets you create standardised software architecture diagrams from a simple text-based syntax. Instead of dragging shapes around in a GUI tool, you describe your system in plain text and the tool renders the diagram automatically. This approach is faster, version-control friendly, and keeps diagrams in sync with code because they live in the same repository.

This tool uses Mermaid.js — the industry-standard open-source diagramming library used inside GitHub, GitLab, Notion, Confluence, and VS Code. Any diagram you create here can be pasted directly into a Markdown file and rendered natively on GitHub.

When to Use Each Diagram Type

• Class Diagram — Designing object-oriented systems. Shows classes, attributes, methods, and inheritance relationships. Use during architecture planning or code review.
• Sequence Diagram — Documenting API calls, authentication flows, or microservice communication. Shows the order of messages between actors and systems over time.
• Use Case Diagram — Communicating system scope to stakeholders. Shows what a system does from the user's perspective, without implementation details.
• State Diagram — Modelling stateful systems like order lifecycles, user sessions, or UI component states. Shows all states and the transitions between them.
• ER Diagram — Designing or documenting database schemas. Shows entities (tables), their attributes, and the relationships and cardinalities between them.
• Activity / Flowchart — Mapping business processes, algorithms, or user journeys. Useful for onboarding docs, decision trees, and CI/CD pipelines.

Frequently Asked Questions