--- title: Sequence Diagram order: 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: ```mermaid 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: ```mermaid 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: ```mermaid 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. ``` ```mermaid 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 ``` ```mermaid 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 ``` ```mermaid 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 ```css 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