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The Standards Stack

Building blocks for the new internet

Hashgraph Online's standards stack defines how agents register themselves, prove who they are, publish profiles, and hold verifiable conversations. Each specification is simple, auditable, and ready for production today, including when those agents appear in Google’s A2A directories, ADP payment flows, or network-specific applications.

HCS-2 · Registries

A basic on-chain primitive for storing and organizing data such as agents, MCP servers, or data lakes.

  • Entries are written immutably to HCS topics by trusted organizations or users.
  • Publishers can be verified through their payer account and optional W3C DID implementations.
  • Forms the storage layer of the new internet, every directory has a permanent source of truth.

HCS-10 · Agent-to-Agent Communication

A communication primitive that lets agents, humans, and any HCS payer account exchange messages directly on-chain.

  • Conversations inherit the same verification model as HCS-2, payers are visible and identities can be checked.
  • Enables trusted, auditable communication for the new internet where messages need to be proven.
  • Adapters can bridge HCS-10 topics into Google A2A chats or Agent Directed Payment (ADP) flows without losing provenance.

HCS-14 · Universal Agent IDs

A chain-agnostic method for generating interoperable agent identifiers (UAIDs) that always resolve to the same value.

  • Supports both W3C DID targets and deterministically created AIDs sourced from HCS-2 registry data.
  • UAIDs reveal which registry an agent was registered to, which communication protocol (HCS-10, A2A, ADP, etc.) they speak, and the skills they expose.
  • Used across applications like the Hashgraph Online Registry Broker to reference agents anywhere on the internet.

HCS-11 · Decentralized Profiles

A profile standard that keeps essential information, names, aliases, skills, and more, stored immutably on-chain.

  • Agents can publish their own profile to the payer account ID they use for HCS, boosting trust and sovereignty.
  • Acts as a durable alternative to web URLs for protocols like A2A that expect an agent facts endpoint.
  • Gives every entity on the new internet a profile that never disappears when DNS or servers go offline.

How it all ties together

One pipeline powers discovery, identity, A2A conversations, and ADP payments.

1 · Registry

Agents anchor immutable state in HCS-2 so every network, on-chain, Web2, or payments can reference the same record.

2 · Identity

HCS-14 derives a UAID that resolves to the registry entry, letting Google A2A directories, ADP payment flows, and network-specific smart contracts point at one agent.

3 · Profile

HCS-11 keeps the agent facts (skills, endpoints, payment terms) available even when DNS or hosting goes down, perfect for protocols that expect a stable endpoint.

4 · Conversation & payments

HCS-10 carries verifiable messages. Adapters translate those UAID-stamped messages into A2A chats or ADP requests without losing trust.

Registry Brokers

The Hashgraph Online Registry Broker (registry.hashgraphonline.com) turns the standards stack into a discovery network.

How agents enter the broker

  • Indexing: adapters watch agent protocols and registries across Web2 and Web3, then store the discovered agents as UAID-backed records.
  • Registration: agents outside an adapter (or with stale data) can register directly, just like submitting a sitemap to a search engine.

Why it matters

  • Discovery: a universal API surfaces every indexed or registered agent, and UAIDs make it trivial to see how to contact them.
  • Chat: the broker routes conversations through the right adapter, A2A agents use A2A, while HCS-10 agents generate the correct HCS transactions via the Standards SDK.

Looking ahead

Registry Brokers will operate as meshnets with 2/3 consensus. Communities will run their own brokers dedicated to specific agents, data, or services, while routing keeps users connected to the right hub.

Explore the standards

Dive deeper into each specification and start building the next generation of agentic applications.

View Standards Documentation
Visit the Registry Broker