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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!
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
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!
Styling
Styling of the 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;
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 configuration params:
Param | Description | 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 |