PlantUML is a component that allows you to quickly write:

• Sequence diagram

  @startuml
  Alice -> Bob: Authentication Request
  Bob --> Alice: Authentication Response
  Alice -> Bob: Another authentication Request
  Alice <-- Bob: Another authentication Response
  @enduml

  

• Usecase diagram

• Class diagram

• Object diagram

• Activity diagram (here is the legacy syntax)

• Component diagram

• Deployment diagram

• State diagram

• Timing diagram

GitHub - plantuml/plantuml: Generate diagrams from textual description
Official Javadoc Documentation: Overview (plantuml 1.2024.7beta2 API)