Tags are used by Ohloh to aid in search discovery, in the "Browse Projects By Tags" feature available as an option on the project search results page, and to help determine project similarity through shared tags.
In order to encourage careful choice of tags, Ohloh limits the number of tags per project to 20. You'll need to pick and choose the right tags to make the project easy to discover, establish similarity, and at the same time highlight unique and differentiating aspects.
To add a tag, enter it into the Add a Tag box. Ohloh will suggest tags already in use based on the text you enter.
Ohloh shows you projects with similar tags as an assist in selecting good tags. By seeing the tags of similar projects, you can see how Ohloh's tagging will identify similar projects, while also choosing some tags that differentiate this one from others like it.
Of course, you are able to add a new tag that is not already in use, but we strongly encourage you to pick from the existing tag set whenever possible.
For projects tagged prior to the implementation of the 20 tag limit, those tags are grandfathered in, but when you edit a project' with more than 20, you'll be required to reduce the number to 20 or fewer.