mermaid/docs/content/sequenceDiagram.md

title	order
Sequence Diagram	3

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. The code snippet below:

%% Example of sequence diagram
sequenceDiagram
    Alice->>John: Hello John, how are you?
    John-->>Alice: Great!

Renders the following diagram:

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

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:

%% Example of sequence diagram
sequenceDiagram
    participant John
    participant Alice
    Alice->>John: Hello John, how are you?
    John-->>Alice: Great!

Renders to the diagram below:

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

-> which will render a solid line without arrow

--> which will render a dotted line without arrow

->> which will render a solid line with arrowhead

-->> which will render a dotted line with arrowhead

-x which will render a solid line with a cross at the end (async)

--x which will render a dotted line with a cross at the end (async)

Notes

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

See the example below:

%% Example of sequence diagram
sequenceDiagram
    participant John
    Note right of John: Text in note

Renders to the diagram below:

sequenceDiagram
    participant John
    Note right of John: Text in note

It is possible to break text into different rows by using <br/> as a line breaker.

%% Example of sequence diagram
sequenceDiagram
    participant John
    Note left of John: Text in note spanning several rows.

sequenceDiagram
    participant John
    Note left of John: Text in note spanning several rows.

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

%% Example of sequence diagram
sequenceDiagram
    Alice->John: Hello John, how are you?
    loop Reply 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 optionat (if without else).

opt Describing text
... statements ...
end

See the example below

%% Example of sequence diagram
    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

Styling

Styling of the a sequence diagram is done by defining a number of css classes. During rendering these classes are extracted from the

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;
    stroke: #CCCCFF;
    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 configration params:

Param	Descriotion	Default value
mirrorActor	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 unwantewd clipping which is why this config param exists.	1