AI sequence diagram generator.
For when the question is not what the components are but in what order they talk, and what happens when step four fails.
What a sequence diagram shows
Participants across the top, time running downward, and messages between them as horizontal arrows. It is the right diagram whenever ordering is the thing you are trying to explain: an authentication handshake, a checkout, a retry path, a distributed transaction with compensation. It is the wrong diagram for showing what a system is made of, because it says nothing about structure.
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.
The failure branch is the useful half
Almost every hand-drawn sequence diagram shows the happy path and stops. The interesting content is what happens when a participant does not respond: whether the caller retries, how it knows the operation was not applied twice, and which participant is left holding inconsistent state. Drawing the alternative flow alongside the main one is where a sequence diagram earns its place in a design doc.
From an API spec or from code
An OpenAPI document or route definitions supply the participants and the operation names accurately, so the diagram uses real endpoint names rather than approximations. The ordering is not in either source, since a spec describes endpoints and not journeys, so that part comes from your description.
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.
Sequence diagram notation
| Element | What it means |
|---|---|
| Lifeline | A participant, drawn as a vertical line down the page |
| Activation bar | The period a participant is doing work |
| Solid arrow | A synchronous call, the caller waits |
| Dashed arrow | A return, or an asynchronous message |
| Open arrowhead | Asynchronous: the sender does not block |
| alt fragment | Alternative paths, such as success and failure |
| loop fragment | A repeated interaction, such as polling or retry |
| Cross at the end of a lifeline | The participant is destroyed or the connection closes |
Try it
Questions
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