Annotations are semi-structured as there is no formal registration process for the namespace and key. Sitepoint have a good article on the Twitter annotation format. This post is an attempt to collate some annotation ideas into a unified place.

There are already some annotations contained in tweets. These include:

• username
• in-reply-to tweet
• timestamp
• location
• contributors

Here are some more. Some day I may clean this up and try to define a standard format and namespace.

• Mood (happy, sad)
• Changed mood (before-after)
• Weather
• Privacy level
• Image/video/sound clip URL
• General URL
• Licence (how can other people sue your tweet?)
• Copyright holder
• Distribution (global / specific country)
• Joke
• Source / attribution
• Current transport (walking, driving, train, etc)
• Traffic
• Split personality
• Translation (including to non-geek)
• Product price
• Special offer / discount
• For sale / wanted
• Currency
• Rating
• Event date/time
• Topic or category (if you generally tweet about a few categorizable topics)
• Group ID (many tweets in the same group could be shown as 1 in supporting clients)
• Vote / poll ID (vote for an option in a poll)
• Proxy (allow other people to use your account, like cotags)
• Question / answer
• Listening to artist / album / song

Feel free to add your own ideas in the comments.