UML diagrams online, every type on one board
Class, sequence, activity, state machine — and the rest of the notation, with real compartments, real relationships, and your team editing beside you.
Backend engineers
Sketch the service boundary before the PR, not after. A sequence diagram settles a retry argument faster than three paragraphs in a thread.
Architects
Keep component and deployment views next to the classes they describe, in one model, with roles that let reviewers comment but not redraw.
Tech leads onboarding
Hand a new joiner a link, not a folder of stale PNGs. They can comment on the shape they don't understand.
Why bother with real notation
Because a diagram is an argument, and a sloppy one wins anyway. Draw a line between two boxes and everybody reads a different relationship into it — owns, uses, becomes — and the disagreement only surfaces months later, in code. UML exists so the line means one thing, and so the person who wasn't in the room reads what you meant.
That is worth the rigor for a design review, an onboarding doc or an RFC — and not worth it for a five-minute sketch. Here you don't have to choose up front. The freeform board and the notation sit on the same canvas, so the sketch that turns out to matter hardens into a class diagram instead of being redrawn somewhere else.
Start from the diagram you need
Every card opens a board with that notation ready to go.
Every element, named
Class diagrams
Sequence diagrams
Activity diagrams
State machines
Use cases
Also on the same board
Draw your first class diagram
Free, no install, no credit card. Bring the team when you're ready.
Start diagramming — free