---
title: Lexicons and integrations
description: The open schemas that define what each record type contains, and the apps that already read or write Sifa's lexicons.
---

A **lexicon** is the schema for one type of Atmosphere record. It says, in machine-readable form: a `id.sifa.profile.position` record must have a `title`, a `companyName`, may have a `startDate`, etc. Lexicons are how any app on the network knows whether the data it just received is well-formed.

## Why lexicons matter

Lexicons are the contract between apps. When Sifa publishes the `id.sifa.profile.position` lexicon, it's committing to: "any record in this collection will look like this." Other apps can read those records confidently, build features on top of them, and skip asking Sifa for permission.

That's the part that makes an open network actually open. Without published schemas, apps would have to reverse-engineer each other's data, and the moment one app renamed a field everything would break. With lexicons, every change is versioned, public, and signposted.

## Where Sifa's lexicons live

All Sifa schemas live in [singi-labs/sifa-lexicons](https://github.com/singi-labs/sifa-lexicons), an MIT-licensed public repo. Each schema is a JSON file with field types, required fields, validation constraints, and human-readable descriptions.

The namespace is `id.sifa.*`. Currently published:

- `id.sifa.profile.self` and 12 sub-types covering positions, education, skills, certifications, projects, volunteering, publications, courses, honors, languages, external accounts, and the user's location.
- `id.sifa.project.*`: projects with multiple contributors.
- `id.sifa.endorsement`: peer endorsements based on real-world interactions.
- `id.sifa.graph.follow` and `id.sifa.graph.connection`: the Sifa-specific follow / connection graph.
- `id.sifa.auth*`: auth flows for Sifa's meet feature.
- `id.sifa.meeting`: meeting records from the handshake / meet flow.

The exact list and schema details are in the repo. We don't restate them here because the repo is the source of truth.

## Apps that already use Sifa lexicons

Because the schemas are public, any Atmosphere app can read or write them. Today:

- **Sifa itself**: the primary writer. Everything in your profile editor produces `id.sifa.*` records.
- **[pdsls.dev](https://pdsls.dev)**: generic record browser, displays any lexicon including `id.sifa.*`.
- **Atmosphere browser extensions**: some show your Sifa profile inline when you hover over an Atmosphere handle anywhere on the web.

We expect more over time. If you build something that reads or writes `id.sifa.*` records, [open an issue](https://github.com/singi-labs/sifa-lexicons/issues) and we'll add it here.

## Lexicons Sifa reads (but doesn't own)

Sifa isn't just a publisher. It also reads from other apps' lexicons to render your activity feed and rich profile data. The main ones:

- `app.bsky.*`: [Bluesky](https://bsky.app) posts, follows, reposts, profile data.
- `forum.barazo.*`: Barazo forum posts and reactions (Sifa surfaces the Barazo activity that's relevant to a profile).
- `sh.tangled.*`: [Tangled](https://tangled.org) repos, issues, pull requests.
- `events.smokesignal.*`: [Smoke Signal](https://smokesignal.events) calendar events you've RSVP'd to.
- `pub.leaflet.*`: [Leaflet](https://leaflet.pub) publications and articles.
- `whtwnd.blog.*`: [WhiteWind](https://whtwnd.com) blog posts.
- `community.lexicon.calendar.rsvp`, `community.lexicon.location.*`: shared community lexicons.
- `site.standard.publication`: [Standard.site](https://standard.site) publication records (see [Standard.site cards](/docs/standard-site-cards)).
- …and more as new Atmosphere apps launch.

The full list of record types Sifa treats as "activity" (and how each is categorised) lives in [`@singi-labs/sifa-sdk/tokens`](https://github.com/singi-labs/sifa-sdk). The [Activity feed](/docs/activity-feed) page renders that list dynamically. When sifa-sdk adds support for a new app, the page updates automatically.

## Want to go deeper

- [Your data on a provider](/docs/your-data-on-a-provider): how lexicons connect to actual stored records.
- [Apps, AppViews, and the firehose](/docs/apps-appviews-firehose): how an app turns raw records into a rendered page.
- [What is the Atmosphere?](/docs/what-is-the-atmosphere): the bigger picture.