Each line in a sequence diagram consists of two columns (i.e. entities), an arrow (i.e. direction of flow), and a message. The two columns are separated by the > arrow and the message is prepended with the :.

Here is an example:

Web App > DB: Start transaction

Here are the types of arrows:

Arrow Syntax Description
> Left-to-right arrow
< Right-to-left arrow
<> Bi-directional arrow
- Line
-- Dotted line
--> Dotted arrow

Each line is parsed in sequential order from top to bottom and rendered in the diagram the same way.

Column names are required to be unique. If a line refers to a column name that hasn't been used in prior lines, a new column will be created.


Properties are key-value pairs enclosed in [ ] brackets that can be appended to column names. Properties are optional.

It is possible to set multiple properties like shown below:

Web App [icon: monitor, color: blue] > DB [icon: database, color: green]: Start transaction 

Here are the properties that are allowed:

IconAttached iconsIcon names (e.g. aws-ec2). See Icons page for full list.
ColorStroke and fill color, when possibleColor name (e.g. blue) or hex code (e.g. #000000)

Here are the lists of icon names: