Simple signals

Draw a signal from one participant to another like this:

    Alice->Bob: Authentication Request
    Bob-->Alice: Authentication Response
                

The participants are automatically created when they are used. Use the "-->" syntax to draw a dotted line.

Changing the order of participants

If you want to participants to be shown in a different order than they are used, declare them first using the participant keyword. You can also rename them this way to save typing.

    participant Bob
    participant Alice
    participant "I have a really\nlong name" as L

    Alice->Bob: Authentication Request
    Bob->Alice: Authentication Response
    Bob->L: Log transaction
                

Signal to Self

A participant can send a signal to itself. This will result in an arrow that turns back on itself.

You may break the text into multiple lines by using "\n".

    Alice->Alice: This is a signal to self.\\nIt also demonstrates \\nmultiline \\ntext.
                

Grouping signals together

You can group signals together using the alt/else, opt, and loop keywords. All of them can take a text description that will be displayed in the group header. Use the end keyword to signal the end of a group. The groups may be nested to any depth.

    Alice->Bob: Authentication Request
    alt successful case
        Bob->Alice: Authentication Accepted
    else some kind of failure
        Bob->Alice: Authentication Failure
        opt
            loop 1000 times
                Alice->Bob: DNS Attack
            end
        end
    else Another type of failure
        Bob->Alice: Please repeat
    end
                

Notes in the diagram

You can add notes to your diagram. Notes can be placed to the left of a participant or to the right of a participant. In addition, you can centre a note over one or more participants.

If a note contains more than one line, it will be not be word-wrapped. Instead, it will be formatted exactly as written.

    entity Alice
    entity Bob

    note left of Alice 
        This is displayed 
        left of Alice.
    end note
    note right of Alice: This is displayed right of Alice.
    note over Alice: This is displayed over Alice.
    note over Alice, Bob: This is displayed over Bob and Alice.
                

Lifeline Activation and Destruction

Use the activate and deactivate keywords to denote object activation. While activated, the participant's lifeline will be highlighted. The activate/deactivate keywords will apply to the previous signal.

You can use the destroy keyword to destroy a participant. The participant's lifeline will end at the previous signal.

    User->A: DoWork
    activate A
    A->B: <<createRequest>>
    activate B
    B->C: DoWork
    activate C
    C-->B: WorkDone
    destroy C
    B-->A: RequestCreated
    deactivate B
    A->User: Done