Sequence Diagram Online — Free UML Sequence Diagram Tool
Create sequence diagrams directly in your browser using plain text. No account, no install, no limits. Type your diagram source on the left and watch the rendered diagram update in real time on the right. Export as PNG or SVG, or share a link with your team.
What this sequence diagram tool does
Text to diagram
Write your flow in a simple plain-text syntax. The diagram renders live as you type — no manual drawing required.
Full UML support
Participants, actors, synchronous and async messages, activation bars, notes, loops, alt/else, opt, and group fragments.
Export PNG & SVG
Download a high-resolution PNG for documents and presentations, or an SVG for vector-quality output.
Shareable links
Click Share to get a URL that encodes the full diagram. Send it to a colleague and they see the exact same diagram.
Zoom & pan
Navigate large diagrams with mouse wheel zoom and click-drag panning. Fit to screen in one click.
No install required
Runs entirely in your browser. Works on any modern browser on any operating system. Completely free.
How to create a sequence diagram online
Declare your participants. Use participant Browser or actor User to define who is involved. The order you declare them sets the left-to-right column order.
Add messages between them. Write Browser->Server: GET /api for a solid arrow, or Server-->Browser: 200 OK for a dashed return. Use ->> and -->> for open arrowheads.
Add structure with fragments. Wrap steps in loop, alt/else, opt, or group blocks to show conditional and repeating logic.
Export or share. Click PNG or SVG to download the diagram, or click Share to generate a link you can paste anywhere.
Common use cases
Sequence diagrams are used across software engineering, architecture, and documentation. Common scenarios include:
Frequently asked questions
What is a sequence diagram?
A sequence diagram is a type of UML (Unified Modeling Language) diagram that shows how a set of participants — users, services, databases, or any system component — communicate with each other over time. It captures the order of messages exchanged, making it one of the most widely used diagrams for documenting software behaviour.
Can I create a sequence diagram online for free?
Yes. This tool is completely free to use with no account, no subscription, and no usage limits. Everything runs client-side in your browser.
Do I need to install anything?
No. Open the page in any modern browser and start diagramming immediately. Nothing is downloaded to your machine.
What syntax does this tool use?
The tool uses a human-readable plain-text syntax. Declare participants, write messages using arrow notation (->, -->, ->>, -->>), and wrap blocks in fragments like loop, alt, opt, and group. Click the Help button for a full reference with examples.
Can I use this for UML diagrams?
Yes. The tool supports the core UML sequence diagram notation: participants, actors, synchronous and asynchronous messages, activation lifelines, combined fragments, and notes.
How do I export my sequence diagram?
Use the PNG button in the toolbar to download a high-resolution raster image, or the SVG button for a scalable vector image. Both export immediately without any account required.
Can I share my diagram with colleagues?
Yes. Click the Share button to generate a URL. The entire diagram source is encoded directly in the link — no server-side storage is needed. Anyone with the link opens the same diagram.
Is this tool suitable for software architecture documentation?
Yes. Engineers, architects, and technical writers use this tool to document APIs, microservice interactions, authentication flows, and system integration points. The plain-text source also works well alongside code in version-controlled documentation.