William Jin 
Looking for a complete guide to Bluesky terms and definitions? This comprehensive glossary explains everything you need to know about Bluesky social network terminology, from basic features to advanced AT Protocol concepts. Whether you’re a new user or experienced with decentralized social media, this guide breaks down all the essential Bluesky vocabulary, technical terms, and platform-specific language to help you better understand and use the network.
A
Algorithm
An algorithm is a set of rules and instructions that computers use to process information and make decisions. On social media platforms like Bluesky, algorithms play a crucial role in determining what content users see in their feeds.
Traditionally, social media feeds displayed posts in reverse chronological order - showing the newest posts first. However, modern platforms use sophisticated algorithms to curate and personalize content.
What makes Bluesky unique is its approach to algorithmic feeds. Unlike other social networks that force users to use a single algorithm, Bluesky embraces “algorithmic choice.” This means users can choose from different custom algorithms created by the community to sort and filter their feed content.
These custom algorithms, known as “custom feeds” on Bluesky, give users unprecedented control over their social media experience. Users can follow multiple custom feeds, each using different algorithms to surface content based on various criteria like topics, engagement levels, or user preferences.
AppView
An AppView is a specialized application within the Bluesky Atmosphere that provides a unique way to view and interact with the social network. The term “AppView” reflects its core function - offering one perspective or view of the network’s data. While the original data is stored in repositories (data repos) managed by Personal Data Servers (PDSes), AppViews can display this information in multiple customized ways.
Think of AppViews as similar to search engines on the internet - they collect and organize data from across the entire Bluesky Atmosphere to create user interfaces. However, AppViews go beyond just displaying information. They can also interact with users’ Personal Data Servers (PDSes) to publish content and updates to their repositories. This two-way communication happens through a secure OAuth login process, enabling a complete application experience.
Source: https://atproto.com/guides/glossary#app-view
AT Protocol
The AT Protocol (Authenticated Transfer Protocol) is the foundational technology that powers Bluesky’s decentralized social network. What makes it unique is its authentication system - every piece of user content is cryptographically signed by the creator, enabling secure content distribution across multiple servers while maintaining data authenticity without requiring direct server communication.
Interestingly, the name “AT Protocol” serves a dual purpose - it represents both the authentication capabilities (“Authenticated Transfer”) and cleverly references the ”@” symbol commonly used in social media, reflecting its design for social networking applications.
Source: https://atproto.com/guides/glossary#at-protocol
Atmosphere
The Atmosphere refers to the complete ecosystem and network built around the AT Protocol. This includes all the applications, services, tools, and communities that use and interact with the protocol. Just like Earth’s atmosphere contains different layers and elements working together, the AT Protocol Atmosphere encompasses the entire interconnected system of users, developers, servers, and applications that make up the Bluesky social network.
Source: https://atproto.com/guides/glossary#atmosphere
B
Banner Size
The optimal Bluesky banner size is 1500 x 500 pixels, which provides the best quality and display across all devices. This recommended banner dimension ensures your profile looks professional and polished.
For the best results, your Bluesky banner image should be:
- Exactly 1500 x 500 pixels in size
- Saved as a JPG or PNG file format
- Under 1MB in file size for fast loading
The banner display adapts responsively based on device:
Desktop/Laptop View:
- Full width display at 1500 pixels
- Minor cropping occurs at top and bottom edges
- Maintains high resolution appearance
Mobile Device View:
- Full height display at 500 pixels
- Slight cropping on left and right sides
- Optimized for vertical viewing
Design Best Practices:
- Center important visual elements like text and logos
- Use the middle section for key design components
- Add background images or patterns to fill outer edges
- Account for potential cropping in layout
Following these banner size guidelines will help optimize your Bluesky profile’s visual appearance across all platforms and devices.
Blob
In the Bluesky ecosystem, Blobs (Binary Large Objects) are a fundamental type of unstructured data that gets stored within repositories. These Blobs play a crucial role in handling media content on the platform, primarily serving as storage containers for multimedia files like images, videos, audio files, and other binary data. This efficient storage system allows Bluesky to manage and serve media content seamlessly across the network.
Source: https://atproto.com/guides/glossary#blob
C
Character Limit
The maximum number of characters allowed in a Bluesky post. Currently set at 300 characters per post.
CID
Content Identifier - a unique hash that represents content in the AT Protocol. Used to verify data integrity and link to specific content.
Source: https://atproto.com/guides/glossary#cid-content-id
Collection
Collections in Bluesky are organized storage containers that hold JSON records within a data repository. Think of them like folders that store related data in an ordered way. Each collection has a unique identifier called an NSID (Namespace Identifier) that connects it to a specific Lexicon schema, which defines the structure and rules for that data. Collections are essential for organizing different types of content like posts, follows, and profile information in a systematic way on the Bluesky network.
Source: https://atproto.com/guides/glossary#collection
D
DAG-CBOR
DAG-CBOR (Directed Acyclic Graph - Concise Binary Object Representation) is an important data serialization format used in Bluesky’s AT Protocol. It converts complex data structures into a standardized binary format that can be efficiently stored and transmitted. DAG-CBOR was specifically chosen for Bluesky because it creates consistent, reliable canonical forms of data - a critical feature for verifying cryptographic signatures and ensuring data integrity across the decentralized network.
Source: https://atproto.com/guides/glossary#dag-cbor
Data Repo
A Data Repository (or “repo”) is a fundamental component of Bluesky that stores all of a user’s public information and content. Each repository contains:
- Collections of JSON records storing posts, likes, follows etc.
- Unstructured binary data like images (blobs)
- A permanent DID (Decentralized Identifier) that uniquely identifies the repository
- Optional domain-based handles that serve as human-readable usernames
Think of a data repository like a personal database that holds everything about your Bluesky presence. The data is secured using advanced cryptography (signed merkle trees) to ensure authenticity and prevent tampering. This security model allows other users to verify that the content really came from you.
Want to learn more? Check out:
Source: https://atproto.com/guides/glossary#data-repo
DID
A DID (Decentralized Identifier) is a permanent, unique digital identity system used by Bluesky to identify user accounts. Unlike traditional usernames that can change, DIDs provide a consistent way to verify and track user identities across the decentralized network.
Key features of DIDs in Bluesky:
- Permanent and unchangeable identifier for your account
- Based on the W3C DID standard for decentralized identity
- Enables secure verification of user identity
- Non-human readable format for technical reliability
- Connects to your account metadata and public keys
Bluesky uses two main types of DIDs:
- did:plc - Bluesky’s custom implementation using their Public Ledger of Credentials
- did:web - A standard web-based DID method
When you interact with Bluesky, your DID connects to important account information like:
- Your Personal Data Server (PDS) location
- Your handle/username
- Your public cryptographic keys
- Other account metadata
For technical details, see the official DID specification and W3C DID standard.
Source: https://atproto.com/guides/glossary#did-decentralized-id
F
Facet
Facets are special elements that enhance and add interactive features to Bluesky posts. They allow posts to include clickable elements like links, mentions, and hashtags in a structured way.
Key types of facets in Bluesky:
- Links: Clickable URLs that take users to external websites
- Mentions: Tags that reference other Bluesky users (e.g. @username)
- Hashtags: Clickable topic tags that help organize conversations
Facets use a JSON-based system to safely embed these interactive elements without requiring complex text parsing. This makes posts more engaging while maintaining security and reliability.
Feed
A feed on Bluesky is a customizable stream of content that displays posts, updates, and interactions from users or topics you choose to follow. Unlike traditional social media platforms where feeds are controlled by a central company, Bluesky’s decentralized approach allows anyone to create and share custom feeds.
Key features of Bluesky feeds:
- Fully customizable content curation
- Support for topic-specific feeds
- User-created and community-driven
- Open-source development options
- Real-time content updates
While user-friendly tools are being developed to help create feeds without coding knowledge, developers can gain complete control over feed creation through programming. Bluesky offers an official Feed Generator Starter Kit to help developers build custom feeds from scratch.
Firehose
The Firehose is Bluesky’s real-time data stream that captures all public posts, likes, follows, and other activity across the entire network. This powerful API allows developers to:
- Access the complete feed of public Bluesky content
- Build custom recommendation algorithms and feeds
- Analyze trending topics and user behavior
- Create innovative third-party applications
- Monitor network activity in real-time
Similar to Twitter’s original public APIs, the Firehose provides comprehensive access to Bluesky’s network data, making it an essential tool for developers building on the platform.
H
Handle
A handle is your unique, human-readable username on Bluesky that makes it easy for others to find and mention you. Think of it like your @username on other social platforms.
Key things to know about Bluesky handles:
- They’re easier to remember and use than DIDs (the permanent account identifiers)
- Must use only standard ASCII characters (letters, numbers, hyphens)
- Can be up to 253 characters long
- Can be changed/updated over time
- Work like domain names to identify your data
- Multiple handles can point to the same account
- Used in Bluesky’s at:// URI system for linking
For example, a handle might look like: @username.bsky.social
Technical resources:
Source: Bluesky Glossary - Handle
J
Jetstream
Jetstream is a powerful streaming service in the Bluesky ecosystem that processes the ATProto Firehose data stream and transforms it into simplified, developer-friendly JSON format. This makes it easier for developers to:
- Build applications and tools using Bluesky data
- Process real-time network activity efficiently
- Access formatted data without complex parsing
- Reduce development time and complexity
- Create innovative third-party integrations
Learn more:
L
Label
Labels in Bluesky are important metadata tags that help moderate and organize content across the platform. These metadata objects can be attached to both repositories and individual records, serving several key purposes:
Key features of Bluesky labels:
- Content moderation and filtering
- Content categorization and organization
- Warning indicators for sensitive content
- Community safety enforcement
- Custom application-specific tagging
Common label values include:
- “nudity” - For adult or NSFW content
- “graphic-media” - For violent or disturbing content
- “spam” - For unwanted promotional content
- “misleading” - For potentially false information
While labels are primarily used for content moderation and safety, developers can also implement custom labels for unique application features and organization.
Technical Resources:
Lexicon
Lexicon is Bluesky’s powerful schema language that defines how data and APIs work in the Atmosphere Protocol (AT Protocol). It serves as the foundation for describing data records and HTTP APIs in a standardized way, similar to popular schema languages like JSON-Schema and OpenAPI.
Key benefits of Lexicon include:
- Standardized data structure definitions
- Clear API specifications
- Improved developer experience
- Enhanced interoperability
- Simplified software development
Developers use Lexicon to ensure their applications can seamlessly communicate and share data within the Bluesky ecosystem. This standardization is crucial for building a decentralized social network.
Learn more about Lexicon:
Source: Bluesky Glossary - Lexicon
N
NSID
NSIDs (Namespaced IDentifiers) are a critical component of Bluesky’s technical infrastructure. These identifiers are used in the Atmosphere Protocol to uniquely identify and organize Lexicon schemas, which define how data is structured across the platform.
Key characteristics of NSIDs:
- Follow a reverse DNS format (e.g., app.bsky.feed.post)
- Provide clear schema governance through domain ownership
- Help avoid confusion with regular domain URIs
- Enable efficient data organization and retrieval
- Support decentralized architecture
The reverse DNS format was specifically chosen to maintain clarity and prevent conflicts with traditional web domains, making the system more robust and developer-friendly.
Technical Resources:
P
PDS
A Personal Data Server (PDS) is a fundamental component of Bluesky’s decentralized infrastructure that stores and manages user data. Think of it as your personal storage space in the Bluesky network.
Key features of a PDS include:
- Secure storage of user data repositories and signing keys
- Optional handle (username) and DID assignment capabilities
- Support for hosting multiple user accounts
- Integration with AppViews for running applications
- OAuth-based account management interfaces
- Active synchronization with Relay servers
One of the most powerful aspects of PDS is that users can self-host their own server, giving them complete control over their data while still participating in the broader Bluesky social network. This aligns with Bluesky’s commitment to data sovereignty and decentralization.
While a PDS primarily focuses on data storage and management rather than running applications directly, it plays an essential role in Bluesky’s federated architecture by communicating with AppViews and synchronizing data across the network through Relays.
Learn more about Personal Data Servers in the official AT Protocol documentation.
R
Record
In Bluesky’s AT Protocol, a Record is a fundamental data structure that stores user-generated content and metadata. Records are JSON documents stored within repository collections, serving as the building blocks for posts, profiles, and other content types on the platform.
Key aspects of Records:
- Structured as JSON documents for flexible data storage
- Contains a required
$typefield that maps to a Lexicon schema - Must match the collection type that contains it
- Enables organized storage and retrieval of social media content
- Forms the foundation for Bluesky’s decentralized data architecture
Records are essential for maintaining data consistency and interoperability across the Bluesky network. Their standardized format, defined by Lexicon schemas, ensures that different parts of the system can reliably communicate and share information.
Technical Resources:
Relay
A Relay is a critical component in Bluesky’s decentralized infrastructure that aggregates and distributes data across the network. Acting as a central hub, Relays efficiently collect data repositories from Personal Data Servers (PDSes) and generate real-time change events that keep the network synchronized.
Key functions of Relays include:
- Aggregating data from multiple PDSes across the network
- Producing a streamlined “firehose” of network changes
- Enabling efficient data fetching for AppViews
- Optimizing network connections and reducing server load
- Supporting scalable data distribution
While Relays provide important optimization benefits, they aren’t mandatory for network operation. AppViews can communicate directly with PDSes when needed, offering flexibility in network architecture. The primary advantage of Relays is their ability to significantly reduce the number of connections required across the network, improving overall performance and scalability.
Learn more about Relays in the official AT Protocol documentation.
S
Skeet
“Skeet” is a popular slang term used by the Bluesky community to refer to posts made on the platform. Similar to how Twitter has “tweets”, Bluesky users have adopted “skeets” as their informal post terminology.
While the term originated organically within the community, it has gained widespread usage despite some resistance from the Bluesky development team. The playful nature of the term and its grassroots adoption exemplifies the strong community culture developing on the platform.
Key points about skeets:
- Informal term for Bluesky posts
- Community-driven terminology
- Widely used across the platform
- Similar to “tweets” on Twitter
- Demonstrates organic community growth
Starter Pack
Starter Packs are curated collections of recommended Bluesky feeds, users, and settings designed to help new users quickly customize their experience. These personalized bundles make it easy for newcomers to discover relevant content and connect with communities that match their interests.
Key features of Starter Packs:
- Customized feed recommendations
- Suggested users to follow
- Optimized settings configurations
- Easy sharing between users
- Interest-based content discovery
The Bluesky team introduced Starter Packs to streamline the onboarding process and help users find their community faster. You can learn more in their official blog post.
Browse and discover Starter Packs that match your interests in the Bluesky Directory.
Learn how to get more followers using Starter Packs: https://skyblaze.app/blog/hot-to-get-more-followers-using-starterpack/
T
TID
TIDs (Timestamp IDentifiers) are a crucial component of Bluesky’s data structure that helps organize and identify posts and content. These unique identifiers serve multiple important purposes:
- Generate unique keys for each post and record
- Maintain chronological ordering of content
- Prevent duplicate posts and data conflicts
- Enable efficient data storage and retrieval
- Support scalable database performance
The TID system is carefully designed to work seamlessly with Bluesky’s distributed architecture while maintaining data integrity across the network. This makes it an essential part of how Bluesky handles millions of posts and interactions efficiently.
For technical details, see the Record keys specification and TID documentation.
X
XRPC
XRPC (Cross-organizational Remote Procedure Calls) was previously used to describe Bluesky’s HTTP implementation in the AT Protocol. However, the term has been deprecated since it essentially refers to standard HTTP usage for API calls.
Key points about XRPC:
- Originally meant to describe atproto’s HTTP implementation
- Stands for “Cross-organizational Remote Procedure Calls”
- Has been deprecated in favor of standard HTTP terminology
- Used for API communication in Bluesky’s infrastructure
- Follows standard HTTP protocols and best practices
For technical documentation, see the HTTP API specification or read more in the official glossary.
Tip
This glossary is regularly updated as Bluesky evolves and introduces new features. Check back for the latest terms and definitions.
