Can I: select tag / reply through Discourse API?

I did not find those things in the documentation, but can I:

  1. Select a topic-tag using Discourse API when asking API to create a new topic?
  2. Reply to the created topic using Discourse API?

Thank you.

Set tags as an array of strings when you HTTP POST. Like:

  title: "Topic title",
  raw: "Raw content",
  category: 1,
  tags: ["tag1", "tag2"]

The same /posts.json endpoint for creating a topic can be used for replying by setting the topic_id. See more on Discourse API Docs.