drawflow.io — Mermaid sequence diagram editor
Diagram

Mermaid Sequence Diagram Editor

Write Mermaid sequence diagram syntax and watch your diagram render instantly. This online sequence diagram editor includes live preview, keyboard-friendly editing, and one-click export to SVG, PNG, or PDF.

How to use the Mermaid sequence diagram editor

  1. 1. Write Mermaid syntax in the editor

    Open the editor panel and type Mermaid sequenceDiagram notation. Define participants with arrows such as Alice->>Bob: Hello to describe messages between actors. The editor accepts standard Mermaid sequence syntax including alt, loop, opt, and activation blocks.

  2. 2. Review the live preview

    As you type, the preview panel renders an SVG diagram in real time. Syntax errors appear inline so you can fix issues before sharing the diagram. Switch diagram themes from the preview toolbar to match your documentation style.

  3. 3. Organize multiple diagrams locally

    Create, rename, and switch between diagrams stored in your browser. Each diagram keeps its own source and theme settings so you can draft several flows without signing in or uploading files to a server.

  4. 4. Export or copy the result

    When the diagram looks correct, export it as SVG, PNG, or PDF from the export menu. You can also copy notation to paste into README files, wikis, or pull request descriptions.

Common use cases

  • API and microservice documentation

    Document request and response flows between clients, gateways, and backend services. Sequence diagrams make it easier for new engineers to understand how endpoints interact during onboarding.

  • Design reviews and architecture discussions

    Sketch authentication flows, payment hand-offs, or retry logic before writing code. A quick diagram helps teams align on ordering, failure paths, and ownership between services.

  • Incident post-mortems

    Reconstruct what happened during an outage by mapping messages between systems. Visual timelines clarify where timeouts, duplicate calls, or missing acknowledgements occurred.

  • Pull requests and RFCs

    Attach a sequence diagram to explain a non-trivial change. Reviewers grasp cross-service impact faster when message order and optional branches are visible.

  • Teaching and workshops

    Demonstrate messaging patterns such as request-reply, publish-subscribe, or saga orchestration. Students can edit syntax live and immediately see how notation changes the rendered diagram.

Frequently asked questions

Is my diagram sent to a server?
No. Diagram source and preview rendering run entirely in your browser. Your notation stays on your device unless you export or copy it elsewhere.
Which Mermaid diagram types are supported here?
This editor focuses on sequence diagrams and related Mermaid syntax used in sequence flows. For flowcharts, state machines, and class diagrams, browse the Templates page and open a starter in the editor.
Can I share a diagram with a teammate?
Export SVG or PNG and attach it to docs, or copy the Mermaid source into your repository. Diagrams are stored locally in your browser rather than as shareable cloud links.
Why does my preview show a syntax error?
Mermaid requires valid keywords, participant names, and fragment blocks such as alt/end. Check the error panel for line hints, then compare your syntax with a template from the Templates page.