AI UML diagram generator.
In practice teams use about four of UML's fourteen diagram types, and this draws those four properly rather than all of them badly.
The UML worth using
UML defines fourteen diagram types and working teams use a handful: sequence for interactions, component for structure, class for domain models, and state for anything with a lifecycle. The others are either specialised or have been quietly replaced by better-fitting conventions such as C4. Treating UML as a vocabulary to borrow from rather than a standard to comply with is what keeps it useful.
How Lucid Train draws one
Describe what you want, or point it at a repository. The agent emits a semantic graph of nodes and edges with no coordinates, and the ELK layout engine computes positions and orthogonal routing. That separation is the reason the output cannot come back with boxes overlapping or arrows crossing through cards, which is the characteristic failure when a language model is asked to place things on a canvas itself. It also means editing is editing the graph: change a component and the layout re-solves rather than drifting out of alignment.
State diagrams are the underused one
Anything with a status column has a state machine, and it is almost never written down: orders, subscriptions, deployments, tickets. Drawing the states and the permitted transitions usually reveals transitions the code allows that nobody intended, which makes this one of the few diagram types that regularly finds bugs.
Specification compliance is not the goal
This produces diagrams that read correctly to an engineer familiar with UML, not diagrams that would pass validation against the specification. If you need formal UML for a regulated deliverable or model-driven code generation, a dedicated modelling tool is the right choice and this is not it.
Local, offline, your models
It runs as a desktop application. Against a local Ollama model the whole thing works offline with no API key and no telemetry, which is the practical difference from every browser-based diagram tool: your architecture never leaves the machine.
UML types, and whether they earn their place
| Type | Use it for | In practice |
|---|---|---|
| Sequence | Interactions over time | Genuinely useful, widely used |
| Component | Structure and interfaces | Useful, often replaced by C4 containers |
| Class | Domain models | Useful for the model, rarely for the code |
| State machine | Lifecycles and transitions | Underused, frequently finds real bugs |
| Activity | Process flow | A flowchart with more notation |
| Use case | Actors and goals | Rare in engineering practice |
| Deployment | Where things run | Usually better as an infrastructure diagram |
Try it
Questions
Is UML still worth using?
As a shared vocabulary, yes: sequence and state diagrams in particular are widely understood and hard to improve on. As a complete method with tooling and model-driven development, it has largely been abandoned for good reasons.
Can it generate a class diagram from code?
Yes, and the result is usually too detailed to be useful. A class diagram of the domain model is worth having; one of every class in a codebase is a worse version of what your IDE already shows.
Does it export PlantUML?
The canvas exports SVG, PNG and Excalidraw. Ask the agent for PlantUML source and it will write it, which is a different artifact from the drawn diagram.
Which UML diagram should I use for architecture?
Component, or step outside UML and use C4 containers, which most teams find clearer for the same job.
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