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.
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:
Actors
If you specifically want to use the actor symbol instead of a rectangle with text you can do so by using actor statements as per below.
Aliases
The actor can have a convenient identifier and a descriptive label.
Grouping / Box
The actor(s) can be grouped in vertical boxes. You can define a color (if not, it will be transparent) and/or a descriptive label using the following notation:
box Aqua Group Description
... actors ...
end
box Group without description
... actors ...
end
box rgb(33,66,99)
... actors ...
end
If your group name is a color you can force the color to be transparent:
box transparent Aqua
... actors ...
end
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 |
--x |
Dotted line with a cross at the end. |
-) |
Solid line with an open arrow at the end (async) |
--) |
Dotted line with a open arrow at the end (async) |
Activations
It is possible to activate and deactivate an actor. (de)activation can be dedicated declarations:
There is also a shortcut notation by appending +
/-
suffix to the message arrow:
Activations can be stacked for same actor:
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:
It is also possible to create notes spanning two participants:
It is also possible to add a line break (applies to text input in general):
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:
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:
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:
It is also possible to nest parallel blocks.
Critical Region
It is possible to show actions that must happen automatically with conditional handling of circumstances.
This is done by the notation
critical [Action that must be performed]
... statements ...
option [Circumstance A]
... statements ...
option [Circumstance B]
... statements ...
end
See the example below:
It is also possible to have no options at all
This critical block can also be nested, equivalently to the par
statement as seen above.
Break
It is possible to indicate a stop of the sequence within the flow (usually used to model exceptions).
This is done by the notation
break [something happened]
... statements ...
end
See the example below:
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:
Entity codes to escape characters
It is possible to escape characters using the syntax exemplified here.
Numbers given are base 10, so #
can be encoded as #35;
. It is also supported to use HTML character names.
Because semicolons can be used instead of line breaks to define the markup, you need to use #59;
to include a semicolon in message text.
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>
.initialize({ sequence: { showSequenceNumbers: true } });
mermaid</script>
It can also be turned on via the diagram code as in the diagram:
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;
}.actor {
textfill: black;
stroke: none;
font-family: Helvetica;
}
.actor-line {
stroke: grey;
}
.messageLine0 {
: 1.5;
stroke-widthstroke-dasharray: '2 2';
marker-end: 'url(#arrowhead)';
stroke: black;
}
.messageLine1 {
: 1.5;
stroke-widthstroke-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 {
: 2;
stroke-widthstroke-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
It is 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.
.sequenceConfig = {
mermaiddiagramMarginX: 50,
diagramMarginY: 10,
boxTextMargin: 5,
noteMargin: 10,
messageMargin: 35,
mirrorActors: true,
; }
Possible configuration parameters:
Parameter | 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 |
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