A fundamental problem with traditional social apps is they don't work together, they're not interoperable. You can't access the photos from one social network via the timeline of another or use your favorite reading app to browse posts on a separate service.

On the Atmosphere, Lexicons make interoperability possible.

The file format of the Atmosphere

If you're a programmer, Lexicons will look familiar as data schemas, the metadata that describes how information is stored and retrieved.

Another way to think about Lexicons is as the file format of the Atmosphere. In the same way that you've likely got several apps on your computer that can read common files like images or text documents, apps on the Atmosphere can read, write, and define their own Lexicons.

The app Anisota is a great example of how Atmosphere apps work differently. On the surface, Anisota looks like a third party client with a very opinionated view of your timeline, the kind of thing that would have been possible to build against the API of a centralized social network.

A closer look reveals there's a game hidden in there, with a collection of several custom Lexicons. Anisota is reading Bluesky timeline data while creating its own gameplay data, with everything stored on the PDS (Personal Data Server), which can be remixed by other applications, while remaining portable to another PDS.

Remixing apps

At Eurosky this week, Sill developer Tyler Fisher showed off a new bookmarking feature that lets you save links from the app's aggregated feed, with the option to also save those links to your PDS. Sill's bookmarks use the same Lexicon as KipClip, so when you save a bookmark in Sill it also shows up in KipClip. If you were so inclined, you could build a link blog that also pulled from those same bookmarks.

Anyone can build a Lexicon. You can create your own from whole cloth, reuse Lexicons from other apps, or use community schemas. Hilary Bauman recently collected and categorized a few dozen apps that define their own Lexicons, and you can use PDSls or Taproot to peer into your own or anyone else's data schemas.

Lexicons represent a fundamental shift in how we think about social data. Rather than being locked into a single platform's idea of a "post" or "bookmark", developers can create their own data types that are portable across the entire network.

This is how the Atmosphere delivers on its promise of breaking down platform silos—not by forcing everyone to use the same apps, but by ensuring the underlying data can flow freely between them.

The beauty of this approach is that innovation doesn't require permission. Sill didn't need to convince a centralized platform to add bookmarking to their API. Anisota didn't need special access to the Bluesky timeline to build a game layer. They simply defined the Lexicons they needed and started building.

As more developers adopt and create their own schemas , the network effects grow stronger, creating an ecosystem where your data truly belongs to you and works wherever you choose to use it.