Social conversation platform Livefyre released today Sidenotes, a new feature that lets publishers add in-line comment threads to their sites. Livefyre has also integrated Sidenotes into Storify, marking the first major product integration to the service, which it acquired last Fall.

Sidenotes works by attaching comments to each paragraph of an article or piece of content. Users can highlight specific text to comment on or reply to other responses. The pop-up box updates in real-time and ranks comments based on the number of upvotes they have received.

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Annotations were one of the first products that Livefyre tested as a young startup, but it waited five years to develop and release it. Livefyre CEO Jordan Krechmer said at the time he didn’t think it was possibly to “completely change the paradigm overnight on how people interact with content.”

Now that Livefyre has a number of major media conglomerate customers and hundreds of thousands of sites using its platform, it’s in a better place to initiate change.

As Livefyre was revisiting its ideas for annotations, sites like Medium and Quartz rolled out their own in-line commenting designs. Livefyre took that as validation for the idea and went heads-down on its own implementations. The startup may not be the first to market, but Krechmer believes that Sidenotes is the first “out of the box experience” for bringing collaborative annotations to any page. Livefyre designed Sidenotes for mobile first, relying on swipe gestures to call up the annotation box.

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Universal Music’s Interscope Geffen A&M plans to add Sidenotes to its artists’ lyric pages in order to add Rap Genius-like functionality to its site. Other beta partners include Salon.com, Fox Business and Fox Sports.

While the technology behind annotations may seem simple, Krechmer noted that it turned out to be an “incredibly complex problem.” Livefyre had to figure out a way to assign individual IDs to each piece of content and track changes so that it can keep comments in place even if an editor makes changes to a page. Sidenotes also had to be ready to accommodate a broad range of page formats and content types for CSS, HTML and ad platforms.

“We had to build this thing to be insanely defensive,” Krechmer said. “How to make them productive on mobile was a user experience nightmare and we spent tons of time on that.”

Livefyre’s blogger partners will receive access to a free non-enterprise version of Sidenotes. Enterprise customers can flip a switch to get the full product right away.

➤ Livefyre adds a real-time review system to its social content service