How does Deduplication work?
The current Leo deduplication skill is content-based (not site or URL based). Leo will read all the articles in your feeds, if the content of 2 (or N) articles overlap by more than 85%, then Leo will consider these 2 (or N) articles as duplicates. Leo will only show you one copy and when you mark that copy as read, all the other copies will be automatically marked as read (and not showed in your Feedly feeds).
You can also learn more about Deduplication in our blog post here: https://blog.feedly.com/deduplication-skill-leo/.
Deduplication is enabled by default, if for any reason you'd like to disable it, you can do so here: https://feedly.com/i/account/leo.
Note: Deduplication doesn't work in 3rd party apps using Feedly as a backend sync service.
Note 2: Deduplication doesn't work within a source/publisher. This is because some sources reuse the same URL for all the articles they publish or publish the same text with different media like videos etc. so at this moment it is not safe to deduplicate within a source, only across different sources.