Explain an interaction one message at a time.

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.

Model APIs, authentication, checkout, and incidents

Sequence diagrams are especially useful when timing and responsibility are more important than static structure. Show a browser calling an API, a service consulting a database, a payment provider returning a webhook, or an on-call engineer coordinating an incident response.

Use message arrows that carry meaning

Choose solid or dotted lines, open or filled arrowheads, and activation arrows. The visual editor produces Mermaid syntax such as ->>, -->>, -), and ->>+ while keeping sender and recipient aliases stable.

Represent loops and alternative paths

Add loop, alt, else, opt, par, critical, and break blocks in the same order readers experience the interaction. The editor checks block balance before serialization and preserves advanced Mermaid lines from the code view.

Export images and version-controlled text

Download SVG for responsive documents, PNG for messages and slides, or PDF for reports. Copy the Mermaid code, fenced Markdown, SVG markup, a PNG image, or a shareable URL. The .mmd and .md downloads keep the diagram editable instead of locking it into a proprietary canvas.

Private, browser-based diagramming

Your actors, messages, and system names are not uploaded to a rendering service. The editor, compressed share payload, draft autosave, and export pipeline run locally in the browser.