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Actors + Messages + Lifelines 100% Client-Side • Private

Build Sequence Diagrams You Can Commit as Text

Map API calls, service interactions, authentication flows, and user journeys visually while generating clean Mermaid sequence syntax.

Sequence Guide

Editable system interactions

Choose a sequence diagram template.

Participants & Actors

0 participants

Sequence Messages

0 rows

Live Mermaid preview

Sequence preview

Preparing chart…

Private · local render

Scrollable preview. Use the arrow keys to pan, Shift with an arrow key to pan further, and Home to return to the top left.

Building your first preview…

The preview updates as you edit.

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Expanded preview

Sequence preview

Document the conversation between systems

Turn an interaction into reviewable Mermaid text.

A sequence diagram makes message order, ownership, repetition, and alternative paths visible. This builder keeps the editable Mermaid source beside the result, so the diagram can live with an API specification, architecture note, issue, or pull request.

01

Name lifelines clearly

Use stable aliases for code and readable labels for the people, browsers, APIs, queues, and databases in the interaction.

02

Show meaningful branches

Use loop, alt, opt, par, break, and critical blocks when control flow matters to the reader.

03

Keep behavior diffable

The generated source stays compact enough to review and update alongside the implementation it explains.

Syntax Pattern

Mermaid sequence syntax

Declare each lifeline once, use arrows for messages, and wrap repeated or conditional behavior in blocks. Open the sequence syntax reference

sequenceDiagram
  actor User
  participant API
  User->>API: Submit request
  alt Valid input
    API-->>User: 200 OK
  else Invalid input
    API-->>User: 400 Bad Request
  end

A free online Mermaid sequence diagram generator

This free sequence diagram generator converts an ordered interaction into a live Mermaid diagram. Start from a working template, then edit actors, participants, messages, arrows, notes, loops, alternatives, parallel paths, and other control-flow blocks. The browser renders the result immediately and keeps the source available for technical documentation.

Frequently Asked Questions

What is a sequence diagram?

A sequence diagram illustrates how processes, services, or actors interact with one another over time in a sequential order.

Can I add synchronous and asynchronous messages?

Yes. Use solid arrows with filled heads (->>) for synchronous calls and dotted arrows (-->>) for responses.

Are loops and conditional branches supported?

Yes. The visual builder supports loop, alt, opt, and par blocks.

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