I can highly recommend http://plantuml.com/ http://plantuml.com/ because it has support for other types of diagrams too, not just sequence diagrams. It's open

I can highly recommend http://plantuml.com/ http://plantuml.com/ because it has support for other types of diagrams too, not just sequence diagrams. It's open source and also cross platform, since it's written in Java. It has command-line interface too and integrates with most popular IDEs. You can host your own rendering server too and just reference your diagrams as URLs (https://github.com/plantuml/plantuml-server https://github.com/plantuml/plantuml-server). There is a 3rd party, independent rendering server integrated with a web editor. I recommend that if you want to quickly test PlantUML: https://www.planttext.com/ https://www.planttext.com/