I also made a similar bot, might be useful!, this one doesn't check every single post, only external links, I didn't want to repost original content or spam communities, so the post only gets one post per hour (which can be changed) and checks the community to see if there's a similar post there already (same link).
Edit: it uses the json page, and filters posts based on upvotes, downvotes, age, etc. It supports multiple subreddits and communities at the same time.