Sequence Diagram

  define Complex System as sys
  define User as usr
  define Sequence Diagram as diagram
  define Other Users as usr2
  begin sys, usr, usr2
  sys ~> usr
  note over usr: "Take time to\nunderstand System"
  usr -> *diagram: Create
  usr -> usr2: Inform
  usr2 <-> diagram: Learn & understand
  usr2 -> sys: Use
  terminators box


Want to draw a Sequence Diagram? Go to the online editor.

This library renders sequence diagrams from code. It is open-source (LGPL-3.0), and including it in a website is as simple as adding the script:

<script src="lib/sequence-diagram-web.js"></script>

If you are using NPM to manage dependencies, you can install with:

npm install --save svg-sequence-diagram

And import with:

import 'svg-sequence-diagram';



Any element with the class sequence-diagram will automatically be converted when the page loads:

  A -> B: foo
  B -> A: bar


Connection Types

title Connection Types

begin Foo, Bar, Baz

Foo -> Bar: Simple arrow
Bar --> Baz: Dashed arrow
Foo <- Bar: Reversed arrow
Bar <-- Baz: Reversed & dashed
Foo <-> Bar: Double arrow
Bar <--> Baz: Double dashed arrow

# An arrow with no label:
Foo -> Bar

Bar ->> Baz: Different arrow
Foo <<--> Bar: Mix of arrows

Bar -> Bar: Bar talks to itself

Foo -> +Bar: Foo asks Bar
-Bar --> Foo: and Bar replies

Bar -x Baz: Lost message

# Arrows leaving on the left and right of the diagram
[ -> Foo: From the left
[ <- Foo: To the left
Foo -> ]: To the right
Foo <- ]: From the right
[ ~> ]: Wavy left to right!
# (etc.)


title Dividers

begin Foo, Bar, Baz

Foo -> +Bar


Bar -> +Baz

divider delay: This takes a while

-Baz --> Bar

divider tear with height 20: Lots of stuff happens

-Bar --> Foo

Notes & State

title Note Placements

begin Foo, Bar

note over Foo: Foo says something
note left of Foo: Stuff
note right of Bar: More stuff
note over Foo, Bar: "Foo and Bar
on multiple lines"
note between Foo, Bar: Link

# in long diagrams, we can add reminders of which agent is which:

text right: "Comments\nOver here!"

state over Foo: Foo is ponderous


title At the Bank

begin Person, ATM, Bank
Person -> ATM: Request money
ATM -> Bank: Check funds
if fraud detected
  Bank -> Police: "Get 'em!"
  Police -> Person: "You're nicked"
  end Police
else if sufficient funds
  ATM -> Bank: Withdraw funds
  repeat until "all requested money
                has been handed over"
    ATM -> Person: Dispense note
  ATM -> Person: Error

Label Templates

autolabel "[<inc>] <label>"

begin "Underpants\nGnomes" as A
A <- ]: Collect underpants
A <-> ]: ???
A <- ]: Profit!

Multiline Text

title "My Multiline

begin Foo, Bar

note over Foo: "Also possible\nwith escapes"

Foo -> Bar: "Lines of text\non this arrow"

if "Even multiline\ninside conditions like this"
  Foo -> "Multiline\nagent"

state over Foo: "Newlines here,


theme sketch

title Mockup

A thing -> +Another thing: Something happens
-Another thing --> A thing: With some response
note right of Another thing: Find out what happens here
end Another thing

Available themes

Short-Lived Agents

title "Baz doesn't live long"

note over Foo, Bar: Using begin / end

begin Baz
Bar -> Baz
Baz -> Foo
end Baz

note over Foo, Bar: Using * / !

# * and ! cause agents to be
# created and destroyed inline
Bar -> *Baz: make Baz
Foo <- !Baz: end Baz

# Foo and Bar end with black bars
terminators bar
# (options are: box, bar, cross, fade, none)

Agent Aliases

define My complicated agent name as A
define "Another agent name,
and this one's multi-line!" as B

A -> B: this is much easier
A <- B: than writing the whole name


define "Name with
**bold** and _italic_" as A
define "Also `code`
and ~strikeout~" as B

A -> B: "_**basic markdown
is supported!**_"

Alternative Agent Ordering

define Baz, Foo

Foo -> Bar
Bar -> Baz

Agent Types

begin User, Application, PostgreSQL

User -> +Application
Application -> +PostgreSQL
-PostgreSQL --> Application
-Application --> User

User is a person
PostgreSQL is a database

Asynchronous Communication

begin Initiator as I, Receiver as R

# the '' syntax allows connections
# to span multiple lines

I -> ...fin1
...fin1 -> R: FIN

# they can even inter-mix!
R -> ...ack1
R -> ...fin2
...ack1 -> I: ACK
...fin2 -> I: FIN

!I -> ...ack2
...ack2 -> !R: ACK


More features are supported. See the online editor’s library and autocomplete features to discover them.

Browser Support

This has been tested in the latest versions of Google Chrome, Mozilla Firefox, and Apple Safari. Versions of Microsoft Internet Explorer / Edge have not been tested and probably won’t work. Any bugs found in a supported browser should be reported in the Issue Tracker.


For more advanced usage, an API is available:


diagram = new SequenceDiagram(code, options);
diagram = new SequenceDiagram(code);
diagram = new SequenceDiagram(options);
diagram = new SequenceDiagram();

Creates a new SequenceDiagram object. Options is an object which can contain:


newDiagram = diagram.clone(options);
newDiagram = diagram.clone();

Creates a copy of the diagram. If options are given, they will override the current diagram’s state (options is passed to the constructor of the new object, so all the same options are available). Note that by default, the namespace will not be cloned (a new unique namespace will be generated). Also the container will not be cloned; you will need to specify one explicitly or manually attach the new diagram at a later point.



Changes the code for the diagram and causes a re-render.


processed = diagram.process(code);

Processes the given code but does not render it. Causes no change to the diagram object. This is mostly useful for debounced rendering with immediate error notifications. The resulting object can be passed to render at a later point.



Forces a re-render of the diagram. Typically this happens automatically. Optionally, the result of an earlier call to process can be provided.



Make a new theme available to the diagram. Any unrecognised themes are replaced with the default theme.

The theme API has not been finalised yet, so this method is not typically useful.


names = diagram.getThemeNames();

Returns a list of names of themes which are available to this diagram. These can be specified in a theme <name> line in the code.


themes = diagram.getThemes();

Returns a list of themes which are available to this diagram.


  begin A, B
  if bored
    A -> +B
    -B --> A
  if still bored
    A -> +B
    -B --> A

Makes the rendered diagram interactive. Currently this means adding a click listener to any groups which causes them to collapse / expand. Try clicking on the example to the right.

The example here has CSS styling applied:

.region.expanded {
	cursor: pointer;
	user-select: none;

.region.collapsed:hover .outline,
.region.expanded:hover .outline {
	fill: rgba(255, 128, 0, 0.5);

It is also possible to enable interactivity using a HTML attribute:

<pre class="sequence-diagram" data-sd-interactive>
  A -> +B
  if something
    -B --> A


svgURL = diagram.getSVGSynchronous(options);

Returns a blob URL which contains the SVG code for the current diagram.

The options can include:


diagram.getSVG(options).then(({url, latest}) => { ... });

Asynchronous version of getSVGSynchronous. This is provided for compatibility with getPNG, which has no synchronous equivalent.

The options can include:

The callback receives an object containing:


diagram.getPNG(options).then(({url, latest}) => { ... });

Generates a PNG image and returns a blob URL.

The options can include:

The callback receives an object containing:


size = diagram.getSize();

Returns an object containing width and height properties, corresponding to the size of the diagram in units.


title = diagram.getTitle();

Returns the document title as a string. All formatting is lost, and newlines are replaced with spaces. Returns a blank string if no title is set.



Same as calling node.appendChild(diagram.dom()).


node = diagram.dom();

Returns the base SVG element which the diagram has been rendered into.



Marks elements generated by the specified line with a "focus" CSS class, which can be used to style them. Only one line can be highlighted at a time. Calling with no parameter (or null) will remove the highlighting.

The outline effect seen in the editor can be achieved by targetting .focus .outline. All elements contain an element with the class "outline", which defines a simple shape surrounding the entire element. For example:

.region.focus .outline {
	stroke-width: 5px;
	stroke: rgba(255, 128, 0, 0.5);


diagram.setCollapsed(line, collapsed, options);
diagram.setCollapsed(line, collapsed);

Marks the given line as collapsed or non-collapsed. If an element defined at that line can be collapsed, it will be modified during the next render. Returns true if a change occurred, or false if the line already had the requested state.

line can also be an array of lines.

By default, calling this method will trigger an automatic render (unless called as a no-op). This can be disabled by passing {render: false} in the options argument.


collapsed = diagram.isCollapsed(line);

Returns true if the given line is marked as collapsed, regardless of whether that line being collapsed has a meaningful impact on the rendered document.


diagram.collapse(line, options);

Shorthand for .setCollapsed(line, true, options).


diagram.expand(line, options);

Shorthand for .setCollapsed(line, false, options).


diagram.toggleCollapsed(line, options);

Toggles the given line’s collapsed status by calling .setCollapsed.



Marks all lines as non-collapsed. Returns true if a change occurred, or false if all lines were already non-collapsed.

By default, calling this method will trigger an automatic render (unless called as a no-op). This can be disabled by passing {render: false} in the options argument.


diagram.addEventListener(type, callback);

Registers an event listener. The available events are:

All mouse events are invoked with a single parameter: the element. This object contains:


diagram.removeEventListener(type, callback);

Removes a previously registered event listener.



Removes all registered event listeners for a given type, or all event listeners for all types.

Similar Tools

There are quite a lot of sequence diagram drawing tools available. If this one doesn’t fit your needs for whatever reason, you might want to take a look at the alternatives: (but also feel free to raise feature requests in the issue tracker!)


Thanks to the other tools mentioned above for inspiring parts of the syntax of this project, and to the Handlee font which is used in the sketch theme.

  theme sketch
  begin User, SequenceDiagram as SD, Parser, Generator, Renderer

  User -> +SD: code

  SD -> +Parser: code
  -Parser --> SD: parsed

  SD -> +Generator: parsed
  -Generator --> SD: generated

  -SD -> +Renderer: generated
  -Renderer -> *DOM: SVG
  User <~> DOM: interaction

  terminators box