Online UML diagram tool

Draw UML class and sequence diagrams, online.

LetDraw is a UML diagram tool that runs in your browser, with a hand-drawn look and real UML arrowheads. Draw classes and lifelines from the UML shape libraries, or generate a diagram from Mermaid code or a short prompt, then edit every box and arrow.

Draw a UML diagram How it works
Shapes · UML class diagram
Shape # x: number # y: number + area(): number Circle - radius: number + area(): number Square - side: number + area(): number
Step by step

How to make a UML diagram in LetDraw

From an empty canvas to a class or sequence diagram your team can review, without leaving the browser.

  1. Open a canvas

    Start blank or pick the UML Class Diagram template, a base class with two subclasses.

  2. Add UML shapes

    Use the UML library for classes, interfaces, packages and states, or the Sequence Diagram library for lifelines and messages.

  3. Set the relationships

    Pick UML arrowheads such as the hollow triangle for inheritance or the diamonds for composition and aggregation.

  4. Share or export

    Review it together in real time, leave comments on any point, or export to PNG, SVG or PDF.

UML from code or a sentence

A UML diagram tool that reads code

Paste a Mermaid class or sequence diagram and LetDraw turns it into editable shapes on the canvas, then exports it back to Mermaid or D2 when you need code again. Or describe your classes in plain words and let the AI draft a UML class diagram with proper relationship heads.

  • Mermaid import for class and sequence diagrams, as editable shapes
  • Native UML arrowheads: hollow triangle, filled and hollow diamond
  • Prompt to Diagram drafts a class diagram from a description
Try it free
sequenceDiagram User->>API: login API->>DB: query API-->>User: token User API DB login query token
What people draw

UML diagrams for design, docs and reviews

The same canvas holds a quick class sketch and a full set of design diagrams for a service.

UML class diagrams

Model classes, fields and methods with visibility markers, and show inheritance and composition at a glance.

Sequence diagrams

Show how a request moves between a user, an API and a database, including async and return messages.

State machines

Draw the states of an order, a ticket or a device and the events that move it from one to the next.

Use case diagrams

Place actors and use cases to agree on scope with product and business people before building.

Components and packages

Sketch modules, components and deployment nodes to explain how a system is split up.

Design reviews

Share the board, pin comments to any spot and walk through the design live with your team.

Questions

UML diagram tool FAQ

Is LetDraw's UML diagram tool free?
Yes. The Free plan includes the full canvas, every diagram type and export to PNG, SVG and PDF, with no credit card. Pro adds more documents, workspaces and AI requests.
Which UML diagrams can I draw?
The UML library has class, interface, enum, package, component, node, state, use case, actor and note shapes. The Sequence Diagram library adds lifelines, activations, and plain, async, return and self messages.
Can I turn Mermaid code into a UML diagram?
Yes. Paste a Mermaid class or sequence diagram and LetDraw draws it as editable shapes and arrows. You can export any diagram back to Mermaid or D2.
Does it use real UML arrowheads?
Yes. Arrows have built-in start and end heads, including the hollow triangle for inheritance and realization, the filled diamond for composition and the hollow diamond for aggregation.

More diagrams you can make

Flowcharts Process diagrams Org charts ER diagrams Network diagrams Kubernetes diagrams AI whiteboard Online whiteboard

Your next UML diagram is one click away.

Open LetDraw in your browser and start modeling. Free, fast, and nothing to install.