Sequence diagrams

A Sequence diagram is an interaction diagram that shows how processes operate with one another and in what order.

Mermaid can render sequence diagrams.

sequenceDiagram
    Alice->>John: Hello John, how are you?
    John-->>Alice: Great!
sequenceDiagram Alice->>John: Hello John, how are you? John-->>Alice: Great!

A note on nodes, the word “end” could potentially break the diagram, due to the way that the mermaid language is scripted.

If unavoidable, one must use parentheses(), quotation marks “”, or brackets {},[], to enclose the word “end”. i.e : (end), [end], {end}.

Syntax

Participants

The participants can be defined implicitly as in the first example on this page. The participants or actors are rendered in order of appearance in the diagram source text. Sometimes you might want to show the participants in a different order than how they appear in the first message. It is possible to specify the actor's order of appearance by doing the following:

sequenceDiagram
    participant John
    participant Alice
    Alice->>John: Hello John, how are you?
    John-->>Alice: Great!
sequenceDiagram participant John participant Alice Alice->>John: Hello John, how are you? John-->>Alice: Great!

Aliases

The actor can have a convenient identifier and a descriptive label.

sequenceDiagram
    participant A as Alice
    participant J as John
    A->>J: Hello John, how are you?
    J->>A: Great!
sequenceDiagram participant A as Alice participant J as John A->>J: Hello John, how are you? J->>A: Great!

Messages

Messages can be of two displayed either solid or with a dotted line.

[Actor][Arrow][Actor]:Message text

There are six types of arrows currently supported:

Type Description
-> Solid line without arrow
–> Dotted line without arrow
Solid line with arrowhead
–» Dotted line with arrowhead
-x Solid line with a cross at the end (async)
–x Dotted line with a cross at the end (async)

Activations

It is possible to activate and deactivate an actor. (de)activation can be dedicated declarations:

sequenceDiagram
    Alice->>John: Hello John, how are you?
    activate John
    John-->>Alice: Great!
    deactivate John
sequenceDiagram Alice->>John: Hello John, how are you? activate John John-->>Alice: Great! deactivate John

There is also a shortcut notation by appending +/- suffix to the message arrow:

sequenceDiagram
    Alice->>+John: Hello John, how are you?
    John-->>-Alice: Great!
sequenceDiagram Alice->>+John: Hello John, how are you? John-->>-Alice: Great!

Activations can be stacked for same actor:

sequenceDiagram
    Alice->>+John: Hello John, how are you?
    Alice->>+John: John, can you hear me?
    John-->>-Alice: Hi Alice, I can hear you!
    John-->>-Alice: I feel great!
sequenceDiagram Alice->>+John: Hello John, how are you? Alice->>+John: John, can you hear me? John-->>-Alice: Hi Alice, I can hear you! John-->>-Alice: I feel great!

Notes

It is possible to add notes to a sequence diagram. This is done by the notation Note [ right of | left of | over ] [Actor]: Text in note content

See the example below:

sequenceDiagram
    participant John
    Note right of John: Text in note
sequenceDiagram participant John Note right of John: Text in note

It is also possible to create notes spanning two participants:

sequenceDiagram
    Alice->John: Hello John, how are you?
    Note over Alice,John: A typical interaction
sequenceDiagram Alice->John: Hello John, how are you? Note over Alice,John: A typical interaction

Loops

It is possible to express loops in a sequence diagram. This is done by the notation

loop Loop text
... statements ...
end

See the example below:

sequenceDiagram
    Alice->John: Hello John, how are you?
    loop Every minute
        John-->Alice: Great!
    end
sequenceDiagram Alice->John: Hello John, how are you? loop Every minute John-->Alice: Great! end

Alt

It is possible to express alternative paths in a sequence diagram. This is done by the notation

alt Describing text
... statements ...
else
... statements ...
end

or if there is sequence that is optional (if without else).

opt Describing text
... statements ...
end

See the example below:

sequenceDiagram
    Alice->>Bob: Hello Bob, how are you?
    alt is sick
        Bob->>Alice: Not so good :(
    else is well
        Bob->>Alice: Feeling fresh like a daisy
    end
    opt Extra response
        Bob->>Alice: Thanks for asking
    end
sequenceDiagram Alice->>Bob: Hello Bob, how are you? alt is sick Bob->>Alice: Not so good :( else is well Bob->>Alice: Feeling fresh like a daisy end opt Extra response Bob->>Alice: Thanks for asking end

Parallel

It is possible to show actions that are happening in parallel.

This is done by the notation

par [Action 1]
... statements ...
and [Action 2]
... statements ...
and [Action N]
... statements ...
end

See the example below:

sequenceDiagram par Alice to Bob Alice->>Bob: Hello guys! and Alice to John Alice->>John: Hello guys! end Bob-->>Alice: Hi Alice! John-->>Alice: Hi Alice!

It is also possible to nest parallel blocks.

sequenceDiagram par Alice to Bob Alice->>Bob: Go help John and Alice to John Alice->>John: I want this done today par John to Charlie John->>Charlie: Can we do this today? and John to Diana John->>Diana: Can you help us today? end end

Background Highlighting

It is possible to highlight flows by providing colored background rects. This is done by the notation

The colors are defined using rgb and rgba syntax.

rect rgb(0, 255, 0)
... content ...
end
rect rgba(0, 0, 255, .1)
... content ...
end

See the examples below:

sequenceDiagram participant Alice participant John rect rgb(191, 223, 255) note right of Alice: Alice calls John. Alice->>+John: Hello John, how are you? rect rgb(200, 150, 255) Alice->>+John: John, can you hear me? John-->>-Alice: Hi Alice, I can hear you! end John-->>-Alice: I feel great! end Alice ->>+ John: Did you want to go to the game tonight? John -->>- Alice: Yeah! See you there.

Comments

Comments can be entered within a sequence diagram, which will be ignored by the parser. Comments need to be on their own line, and must be prefaced with %% (double percent signs). Any text after the start of the comment to the next newline will be treated as a comment, including any diagram syntax

sequenceDiagram
    Alice->>John: Hello John, how are you?
    %% this is a comment
    John-->>Alice: Great!

sequenceNumbers

It is possible to get a sequence number attached to each arrow in a sequence diagram. This can be configured when adding mermaid to the website as shown below:

    <script>
      mermaid.initialize({
        sequence: { showSequenceNumbers: true },
      });
    </script>

It can also be be turned on via the diagram code as in the diagram:

sequenceDiagram
    autonumber
    Alice->>John: Hello John, how are you?
    loop Healthcheck
        John->>John: Fight against hypochondria
    end
    Note right of John: Rational thoughts!
    John-->>Alice: Great!
    John->>Bob: How about you?
    Bob-->>John: Jolly good!
sequenceDiagram autonumber Alice->>John: Hello John, how are you? loop Healthcheck John->>John: Fight against hypochondria end Note right of John: Rational thoughts! John-->>Alice: Great! John->>Bob: How about you? Bob-->>John: Jolly good!

Styling

Styling of a sequence diagram is done by defining a number of css classes. During rendering these classes are extracted from the file located at src/themes/sequence.scss

Classes used

Class Description
actor Style for the actor box at the top of the diagram.
text.actor Styles for text in the actor box at the top of the diagram.
actor-line The vertical line for an actor.
messageLine0 Styles for the solid message line.
messageLine1 Styles for the dotted message line.
messageText Defines styles for the text on the message arrows.
labelBox Defines styles label to left in a loop.
labelText Styles for the text in label for loops.
loopText Styles for the text in the loop box.
loopLine Defines styles for the lines in the loop box.
note Styles for the note box.
noteText Styles for the text on in the note boxes.

Sample stylesheet

body {
    background: white;
}

.actor {
    stroke: #ccccff;
    fill: #ececff;
}
text.actor {
    fill: black;
    stroke: none;
    font-family: Helvetica;
}

.actor-line {
    stroke: grey;
}

.messageLine0 {
    stroke-width: 1.5;
    stroke-dasharray: '2 2';
    marker-end: 'url(#arrowhead)';
    stroke: black;
}

.messageLine1 {
    stroke-width: 1.5;
    stroke-dasharray: '2 2';
    stroke: black;
}

#arrowhead {
    fill: black;
}

.messageText {
    fill: black;
    stroke: none;
    font-family: 'trebuchet ms', verdana, arial;
    font-size: 14px;
}

.labelBox {
    stroke: #ccccff;
    fill: #ececff;
}

.labelText {
    fill: black;
    stroke: none;
    font-family: 'trebuchet ms', verdana, arial;
}

.loopText {
    fill: black;
    stroke: none;
    font-family: 'trebuchet ms', verdana, arial;
}

.loopLine {
    stroke-width: 2;
    stroke-dasharray: '2 2';
    marker-end: 'url(#arrowhead)';
    stroke: #ccccff;
}

.note {
    stroke: #decc93;
    fill: #fff5ad;
}

.noteText {
    fill: black;
    stroke: none;
    font-family: 'trebuchet ms', verdana, arial;
    font-size: 14px;
}

Configuration

Is it possible to adjust the margins for rendering the sequence diagram.

This is done by defining mermaid.sequenceConfig or by the CLI to use a json file with the configuration. How to use the CLI is described in the mermaidCLI page. mermaid.sequenceConfig can be set to a JSON string with config parameters or the corresponding object.

mermaid.sequenceConfig = {
    diagramMarginX: 50,
    diagramMarginY: 10,
    boxTextMargin: 5,
    noteMargin: 10,
    messageMargin: 35,
    mirrorActors: true
};

Possible configuration params:

Param Description Default value
mirrorActors Turns on/off the rendering of actors below the diagram as well as above it false
bottomMarginAdj Adjusts how far down the graph ended. Wide borders styles with css could generate unwanted clipping which is why this config param exists. 1
actorFontSize Sets the font size for the actor's description 14
actorFontFamily Sets the font family for the actor's description “Open-Sans”, “sans-serif”
actorFontWeight Sets the font weight for the actor's description “Open-Sans”, “sans-serif”
noteFontSize Sets the font size for actor-attached notes 14
noteFontFamily Sets the font family for actor-attached notes “trebuchet ms”, verdana, arial
noteFontWeight Sets the font weight for actor-attached notes “trebuchet ms”, verdana, arial
noteAlign Sets the text alignment for text in actor-attached notes center
messageFontSize Sets the font size for actor<->actor messages 16
messageFontFamily Sets the font family for actor<->actor messages “trebuchet ms”, verdana, arial
messageFontWeight Sets the font weight for actor<->actor messages “trebuchet ms”, verdana, arial