Sequence Diagram Generator — type text, get a clean diagram
Make a sequence diagram online by typing plain text. Each line describes a message between participants, and the preview re-renders live — already laid out for presentation, not the cramped default. Free, no signup, exports to SVG and PNG.
This is a quick preview. The full editor adds AI generate, save & share links, every theme, and watermark-free HD export.
Open full editor →What is a sequence diagram?
A sequence diagram shows how participants — users, services, systems — exchange messages over time. Participants sit on vertical lifelines; arrows between them are messages, read top to bottom in the order they happen. It is the standard way to document API flows, authentication handshakes, and any interaction where who-calls-whom-when matters.
Common use cases
Document request/response chains across services — the diagram makes timeouts, retries, and ownership boundaries visible at a glance.
OAuth redirects, token exchanges, payment authorisation — multi-step protocols are exactly what the top-to-bottom message order is for.
Show what actually happened (or should happen) between systems, in a form reviewers can read without tracing code.
Syntax quick reference
The essentials to get productive — paste any of these into the editor above and adapt. For the full grammar, see the sequence diagram syntax reference.
| Syntax | What it does |
|---|---|
participant A as App | Declare a participant with a display name. |
A->>B: message | Solid arrow — a synchronous call or request. |
B-->>A: reply | Dashed arrow — a response or async reply. |
alt … else … end | Branch between alternative outcomes (accepted vs declined). |
loop … end | Repeat a block of messages (polling, retries). |
note over A,B: text | Attach an explanatory note spanning participants. |
Export options
Vector output with fonts inlined — crisp at any zoom, right for docs, READMEs, and the web.
Raster with optional transparent background and up to 4× scale — right for slides and tickets.
One click publishes a share page with the beautified diagram — no file juggling for reviews.
Frequently asked questions
How do I make a sequence diagram online for free?
Type your interaction as text in the editor above — one line per message, like A->>B: request. The preview renders live with a presentation-ready layout, and you can export SVG or PNG without signing up.
What is a sequence diagram used for?
Documenting interactions over time: API request flows, authentication handshakes, payment processing, service-to-service communication, and incident timelines. Anywhere the question is "who calls whom, in what order", a sequence diagram is the right tool.
How do I show branches and loops?
Wrap messages in alt … else … end for alternative outcomes and loop … end for repetition. The example preloaded above shows an accepted-vs-declined payment branch — edit it in place to see the blocks re-render.
What is the difference between a sequence diagram and a flowchart?
A flowchart shows decision logic inside one process; a sequence diagram shows messages between multiple participants over time. If your diagram has lifelines and calls, it is a sequence; if it has decision diamonds and process steps, it is a flowchart — the editor renders both.
Can I generate the diagram from AI output?
Yes. Ask any AI assistant for "a Mermaid sequence diagram of …", paste the code here, and it renders with a beautified layout. There is also a command-line tool and editor plugins, so agents and scripts can export diagrams directly.
Is this sequence diagram maker really free?
Yes. Anonymous use covers live preview, beautify, and SVG/PNG export with a small watermark; a free account removes the watermark. Per-month export quotas are listed on the pricing page.
Ready to make your own?
Open the full editor to save your work, switch themes, and export clean SVG or PNG. No signup.