Discourse now supports composing a new (pre-filled) topic via URL! To compose a new pre-filled topic, modify URL params like this:
This will open composer window pre filled with topic title, body, category and tags.
Try it out live, here on meta!
Also, instead of providing category/subcategory name, you can also specify a numeric
This feature also supports “Start a topic by pasting a link (like Reddit)”, provided that the body is not present, for example:
Want to compose a pre-filled personal message instead? See: Compose a new pre-filled personal message via URL