Verified as of 27 September 2026.
Many people know AT Protocol as the technology Bluesky runs on. The same protocol also underpins tools for writing, organising events, sharing code, streaming video and publishing photography. This guide explains its parts, some active projects and the caveats worth knowing. I collaborate with atproto.eu, a European community around the protocol mentioned below.
A protocol, not an application
AT Protocol, short for Authenticated Transfer Protocol, is an open protocol for social applications. Bluesky is an application and runs a large part of the infrastructure, but it is not the whole protocol.
The design separates elements that a conventional platform usually controls together: identity, data hosting, application, selection algorithms and moderation. That separation makes portability and interoperability possible, although today the experience of most accounts still depends on services run by Bluesky.
The main parts
Identity. Each account has a DID, a canonical identifier designed to persist, and a readable handle, such as name.bsky.social or your own domain. The handle can change without replacing the identity. Real portability depends on the DID method, the keys available and how the services involved work.
PDS. The personal data server hosts the account, its repository and associated files. Records are cryptographically signed. An account can move to another PDS while keeping its DID in supported cases, but the process still calls for care and does not guarantee that every preference in every application will carry over.
Relay. It aggregates posts from different servers and distributes them as a stream so that other services can index them. It is not the only possible form of synchronisation, but it remains a central part of the deployed infrastructure.
AppView. It indexes the data and builds a usable view: profiles, threads, searches, counts and other results. Two applications can start from compatible data and offer different experiences.
Custom feeds. Services that select and order posts according to a criterion. Users can follow and pin them without moving their account.
Lexicons. Schemas that define record types and let different programs interpret their structure. Sharing a protocol does not require every application to understand every lexicon.
Labelling services. They publish signed labels on accounts or content. They are used, among other purposes, in moderation systems. Each person's application and settings determine what effect a label has.
Some uses built on the protocol
There is no official, exhaustive catalogue. Community directories help you discover projects, but they do not certify their security, maintenance or governance. Active services checked in September 2026 include:
- Social networks: Bluesky, mu and Blacksky.
- Writing: Leaflet and WhiteWind.
- Events: Smoke Signal.
- Code: Tangled.
- Photography and video: Flashes and Streamplace.
Identity compatibility does not mean the same features. Each application may have its own terms, privacy policy, moderation, security and business model. Before authorising one, check which permissions it requests.
Europe
Eurosky is a programme of Stichting Modal, a Dutch non-profit foundation. According to its website, it builds and hosts social infrastructure in Europe. On 11 June 2026 it launched mu, a microblogging application compatible with accounts across the ecosystem. A Bluesky account can be used to sign in to mu, and it is also possible to open an account hosted by Eurosky.
An interface being European is not enough to describe the whole data processing chain. You need to check the operating entity, the providers, the declared locations, the contracts and the applicable policy.
atproto.eu describes itself on its own website as an independent, volunteer-run community that brings together people, projects, meetups and data about the protocol in Europe. Its country statistics are experimental estimates, because AT Protocol does not generally record the national location of each account.
How to start
- Choose a provider. You can open an account on Bluesky, Eurosky or another PDS that accepts sign-ups. Compare terms, support, moderation and migration options.
- Use your own domain as your handle, if you have one and can keep control of the DNS.
- Look for starter packs. Starter packs bring together recommended accounts and feeds. Check who created them and do not automatically follow everything in them.
- Choose feeds. Check authorship, criteria, updates and technical dependency before making one your main view.
- Set up moderation. Distinguish between the rules of the application, labelling services and your own blocks, mutes and lists.
- Keep your originals. Portability is no substitute for a backup of important images, texts and files.
What to know first
The deployed core is public
Public repositories contain posts, profiles and social relationships such as follows, likes, reposts and blocks. An application hiding a relationship in its interface does not make it private. Do not publish information on the assumption that it will only be visible within one application.
Bluesky direct messages are not documented as end-to-end encrypted
Bluesky presented its direct messages as private conversations in May 2024. As of this review, I have not found official confirmation of a general rollout of end-to-end encryption. They should be treated as a private feature of the service, not as a channel designed for highly sensitive secrets.
Spaces is still experimental
Atproto Spaces opened an alpha version on 20 August 2026 to synchronise non-public data with restricted access. The documentation warns of possible breaking changes and advises against using it in production. It does not make private any data already published on the open network.
Governance is still in transition
Most accounts use did:plc, whose main directory remains a significant dependency. In September 2025 an independent Swiss association was announced to govern it. I have not found public confirmation that the full transfer has been completed.
Since April 2026 there has been an active IETF working group on Authenticated Transfer. Its initial charter covers public repositories, synchronisation, URIs and requirements for identity systems. This does not automatically turn the whole of AT Protocol, or all its deployed components, into IETF standards.
Figures are not the same as activity
Bluesky reported 41.41 million registered accounts at the end of 2025, including accounts hosted on independent infrastructure. These are registrations, not unique people or active users. Eurosky spoke of more than 44 million potential users in the ecosystem in June 2026; that is a different figure and date, and should not be mixed with the activity metric.
Self-hosting a PDS
It is possible and there is a reference implementation, but it is not a sensible first step for most people. It requires a domain, a reachable server, certificates, backups, email, monitoring, updates and the ability to recover. Hosting other people's accounts adds operational, contractual, data protection and moderation responsibilities.
Your own PDS does not replace relays, indexes, moderation systems or discovery services either. It removes one dependency, not all of them.
Resources in Spanish
The official documentation remains the technical reference. Part of it is available in Spanish, but coverage may be incomplete. The interactive guide by GainForest offers an introduction in Spanish; it is documentation from a project in the ecosystem, not an official specification.
On the open conversation
This guide explains AT Protocol for newcomers and separates what already works from what is still in development. The ecosystem changes quickly. If a feature, a project or a procedure has changed, the guide remains open.