UML Sequence Diagram
A behavioral UML diagram that shows how objects exchange messages over time.
Sequence diagrams show object interactions in a scenario. Lifelines run top to bottom. Arrows are messages. Use them for APIs, checkout flows, and service calls. This gallery page is an example plus a short how-to in UML Diagram Studio. For a long tutorial, read the sequence diagram blog post.
Actor
A user or external system that starts the interaction.
Lifeline
A vertical line showing an object or participant over time.
Message
A call, signal, or return between lifelines.
Activation
A bar on a lifeline showing when that object is busy.
Alt / Loop
Combined fragments for conditions and repetition.
- •API design reviews
- •Onboarding new engineers to a flow
- •Debugging multi-service bugs
- •Documenting auth and payment
Use Cases:
Industries:
Open the free UML diagram tool
Go to the homepage editor. No install is required.
Declare participants
Use actor and participant aliases so names stay short.
@startuml
actor Customer
participant "Order Service" as Order
participant "Payment" as Pay
@endumlAdd messages
Solid arrows are calls. Dashed arrows are returns.
Customer -> Order: Place order
Order -> Pay: Charge card
Pay --> Order: OK
Order --> Customer: ConfirmationPreview and export
Watch the live preview, then export PNG or SVG.
@startuml
actor Customer
participant "Order Service" as Order
participant "Payment Service" as Pay
participant "Inventory" as Stock
Customer -> Order: Create order
activate Order
Order -> Stock: Check stock
Stock --> Order: Available
Order -> Pay: Charge
Pay --> Order: Success
Order --> Customer: Confirmed
deactivate Order
@enduml- ✓One scenario per diagram
- ✓Name participants as real services
- ✓Show failures when they matter
- ✓Avoid drawing the entire system in one sequence