Editing AT URI

'''AT URI''' is the addressing scheme used in the [[AT Protocol]] to reference repositories, collections, and individual records. Using the <code>at://</code> scheme, these URIs provide a consistent way to identify and locate content within the [[ATmosphere]].

AT URIs serve several functions within the AT Protocol. They are used to identify users accross the network, provide references during [[Data repository|repository]] syncing, and standardized linking to AT Protocol content.

Applications typically display [[handle]]-based URIs for readability, but may use [[DID]]-based URIs internally for stability.

== Structure ==
AT URIs follow a simple hierarchical structure:<syntaxhighlight lang="text">
at://{authority}/{collection}/{record-key}
</syntaxhighlight>Where:

* <code>authority</code> is either a [[handle]] (e.g. <code>alice.bsky.social</code>) or a [[Decentralized Identifier (DID)|Decentralized Identifier]] (e.g. <code>did:plc:z72i7hdynmk6r22z27h6tvur</code>)
* <code>collection</code> is a [[Namespaced Identifier (NSID)]] specifying the type of content (e.g. <code>app.bsky.feed.post</code>)
* <code>record-key</code> is a [[Record key (rkey)|record key]] that uniquely identifies a record within the collection.

For example, these two URIs reference the same [[post]]:<syntaxhighlight lang="text">
at://alice.bsky.social/app.bsky.feed.post/3jzfcijpj2z2a
at://did:plc:z72i7hdynmk6r22z27h6tvur/app.bsky.feed.post/3jzfcijpj2z2a
</syntaxhighlight>

== URI Types ==
AT URIs can reference different levels of specificity.

'''Repository URIs''' reference an entire user repository:<syntaxhighlight lang="text">
at://alice.bsky.social
</syntaxhighlight>'''[[Collection]] URIs''' reference all records of a specific type in a repository:<syntaxhighlight lang="text">
at://alice.bsky.social/app.bsky.feed.post
</syntaxhighlight>'''[[Record]] URIs''' reference a specific individual record:<syntaxhighlight lang="text">
at://alice.bsky.social/app.bsky.feed.post/3jzfcijpj2z2a
</syntaxhighlight>

== Technical Characteristics ==
AT URIs comply with the general URI specification ([https://datatracker.ietf.org/doc/html/rfc3986 RFC 3986]). However, they contain some specific constraints. AT URIs must have:

* A maximum length of 8 kilobytes
* No userinfo component (like username:password@)
* No port specifications

AT URI record keys are case-sensitive, while authorities and collections are case-insensitive and normalized to lowercase.

== Implementation Considerations ==
Usage of handles or DIDs in URIs depends on context. Handle-based URIs (<code>at://alice.bsky.social/...</code>) are human-readable but are not permanent. DID-based URIs (<code>at://did:plc:z72i7hdynmk6r22z27h6tvur/...</code>)  are less readable, but provide stable, permanent references. For critical references, using DID-based URIs is recommended to ensure long-term stability.

[[Category:Core concepts]]
[[Category:Network architecture]]