PlantUML - Sequence Diagram samples (with a nice rendering)

sequence-diagram-1.plantuml

@startuml
    ' styles
    skinparam handwritten true
    skinparam monochrome false
    skinparam packageStyle rect
    skinparam defaultFontName FG Virgil

    skinparam shadowing false
    hide footbox

    '
    title Hello World Sequence Diagram
    
    
    actor "Actor"
    participant "service-1"
   

    == Happy path ==

    Actor -> "service-1": print("Hello world!")
    
    activate "service-1" #DarkSalmon
    Actor <-- "service-1" : ok
    deactivate "service-1"

    == Failure ==

    Actor -> "service-1": print("Hello world!")

    activate "service-1" #DarkSalmon
    Actor <-- "service-1" : ko
    deactivate "service-1"
@enduml

See plantuml/uml.