About the Sequence Diagram Maker
Sequence Diagram Maker draws a sequence diagram from text. Write who sends which message to whom, for example User->>Website: Click Buy, and the diagram appears with the participants across the top and the messages down the page in order. Solid and dashed arrows, notes, choices with alt and else, loops and actors are all supported. Start from an example, pick a colour theme and download the diagram as PNG or SVG. It uses the open Mermaid library in your browser, so your text is never uploaded.
Updated October 2026
How to use the Sequence Diagram Maker
- 1Pick an example, or clear the box and begin with sequenceDiagram.
- 2Write each message as Sender->>Receiver: text. Use a dashed arrow Receiver-->>Sender: text for replies.
- 3Declare participants first if you want to control their order and names.
- 4Add notes, alternatives and loops as needed.
- 5Download the diagram as PNG or SVG.
Reading a sequence diagram
Read it from top to bottom. Each vertical line is a participant. Each arrow is a message, and its position shows when it happens. A dashed arrow is usually a reply or a return value. Boxes labelled alt or loop show choices and repetition.
Writing one from scratch
List the participants first, in the order you want them to appear. Then write the main path, one message per line, from the first action to the final result. Add error cases with alt blocks afterwards. Short labels keep the diagram readable.
- participant U as User
- U->>W: Click Buy
- W-->>U: Show receipt
- alt Payment fails ... else ... end
Where they help
Developers use sequence diagrams to explain how an API call moves through services. Product teams use them to map support or onboarding steps. Anyone can use one to explain who has to do what, in which order, for a process with several people or systems.
Related tools
Use the Flowchart Maker for a process with decisions but no timeline of participants, the Mind Map Maker to explore ideas, and the Gantt Chart Maker for scheduling. When you document an API, the JSON Formatter makes request examples easier to read.
Tips for clear diagrams
Keep to five or six participants. Split large flows into several diagrams. Name messages with verbs, such as Send order or Confirm payment, and use notes to explain rules. Choose the Neutral theme for black and white documents.
Features
- Participants and actors
- Solid, dashed and open arrow styles
- Notes, alternatives (alt and else) and loops
- Draws from plain text as you type
- Four colour themes
- Download PNG or SVG
Frequently asked questions
What is a sequence diagram?
A diagram that shows how people or systems interact over time. Participants stand in columns, and messages are drawn as arrows between them from top to bottom in the order they happen.
How do I write a message?
Write Alice->>Bob: Hello. Use two dashes for a dashed arrow, such as Bob-->>Alice: Hi. The text after the colon is the label.
How do I rename a participant?
Declare it first: participant U as User. Later lines can use the short name U, and the diagram shows User.
How do I show an if or else?
Use alt and else: start with alt Condition, add messages, write else Other condition, add more messages and finish with end.
Can I draw a loop?
Yes. Write loop Every minute, add the messages inside and end the block with end.
Why do I get an error?
A line may not follow the rules, for example a missing colon or an unclosed alt block. The message shows the first helpful line.
Is this UML?
Mermaid sequence diagrams follow the main ideas of UML sequence diagrams and are good enough for documentation, though they do not cover every UML feature.
Is my text stored?
No. The diagram is drawn in your browser and nothing is uploaded.