Where does the Agent Card live and what does it describe?

The Agent Card is a JSON document published at /.well-known/agent-card.json on the agent’s domain. It describes the agent’s name, skills, endpoint URL, and security schemes.

How many A2A protocol agents does Wellknown index and how many are live?

Wellknown indexes 2,749 A2A protocol records, with 2,153 currently live, meaning their latest check succeeded within 24 hours.

How does an agent get submitted to or found in the Wellknown index?

Agents can be submitted by proving domain or repository control through claim proofs or discovered automatically by Wellknown fetching their Agent Cards and other sources.

What is the difference between declared and observed data in Wellknown?

Declared data is metadata stated by the publisher, while observed data is what Wellknown measures by checking the agent’s endpoint, such as status and latency.

A2A Protocol Explained: Agent Cards and Indexing on Wellknown

Q: What is the A2A protocol?

The A2A protocol is an open standard that allows AI agents to discover each other and exchange tasks using JSON-RPC. Agents publish an Agent Card describing their identity and capabilities.

Learn what the A2A protocol is, how Agent Cards work, and how Wellknown indexes and finds A2A agents.

Published: October 31, 2026Data as of: October 31, 2026

The A2A protocol, or Agent2Agent protocol, is an open standard that enables AI agents to discover each other and exchange tasks using JSON-RPC. Central to this protocol is the Agent Card, a JSON document published by an A2A agent at the path /.well-known/agent-card.json. This card describes the agent’s name, skills, endpoint URL, and security schemes, allowing other agents and indexes to understand and interact with it.

Key takeaways

The A2A protocol facilitates agent discovery and task exchange via JSON-RPC.
The Agent Card lives at /.well-known/agent-card.json on the agent’s domain.
The Agent Card describes the agent’s identity, capabilities, endpoint, and security.
Wellknown indexes 2,749 A2A protocol records, with 2,153 currently live.
Agents are submitted to or found in Wellknown’s index through self-submission or discovery of their Agent Cards.

What is the A2A protocol?

The A2A protocol stands for Agent2Agent protocol. It is an open protocol designed to enable AI agents to discover each other and exchange tasks. Agents publish a standardized JSON document called the Agent Card at a well-known location on their domain. Communication between agents happens over JSON-RPC, a remote procedure call protocol encoded in JSON.

This protocol allows agents to find peers dynamically and collaborate by sending tasks and responses in a structured way. It is distinct from other protocols like MCP (Model Context Protocol), which focuses on connecting AI applications to tools and data.

What is an Agent Card and where does it live?

An Agent Card is a JSON document that an A2A agent publishes at the path /.well-known/agent-card.json on its domain. This location is standardized so that other agents and indexes know where to look for it.

The Agent Card describes:

The agent’s name
The agent’s skills or capabilities
The endpoint URL where the agent can be contacted
The security schemes the agent supports

By providing this information, the Agent Card enables discovery and interaction with the agent. It acts as a self-description that indexes like Wellknown can read to list and categorize agents.

How does Wellknown read and index Agent Cards?

Wellknown is a live index of AI agents, MCP servers, and tools that actively checks their endpoints. It reads Agent Cards by fetching the JSON document at /.well-known/agent-card.json from the agent’s domain. This allows Wellknown to extract declared metadata about the agent, such as its name, skills, and endpoint.

Wellknown separates declared metadata (what the publisher states) from observed data (what Wellknown measures by checking the endpoint). This ensures transparency about the agent’s current availability and reliability.

How many A2A records does Wellknown hold and how many are live?

As of the latest data snapshot on 2026-10-31, Wellknown holds 2,749 records for the A2A protocol. Out of these, 2,153 are currently live, meaning their latest check succeeded within the last 24 hours. This indicates a high level of active A2A agents reachable on the network.

For comparison, Wellknown’s total index size is 79,658 records, with 24,496 live overall. The A2A protocol represents a significant subset of this ecosystem.

How is an agent submitted to or found in the Wellknown index?

Agents can be submitted to Wellknown’s index through self-submission or discovered automatically by the index:

Self-submission: Publishers can submit their agents by proving control of their domain or repository. Claim proofs include placing a DNS TXT record at _wellknown.YOUR-DOMAIN, hosting a verification file at https://YOUR-DOMAIN/.well-known/wellknown-verify.txt, or placing a .wellknown-verify file at the repository root.
Discovery: Wellknown discovers agents by scanning known sources such as the MCP registry, npm, PyPI, GitHub, and specifically by fetching Agent Cards at /.well-known/agent-card.json (source labeled as a2a_card).

Once an agent is indexed, it can be searched, resolved, and checked for status through Wellknown’s HTTP API endpoints and MCP server tools.

Summary

The A2A protocol enables AI agents to find and communicate with each other by publishing an Agent Card at a standardized location. Wellknown reads these Agent Cards to index agents, currently holding 2,749 A2A records with 2,153 live. Agents enter the index via self-submission or discovery, with domain control verification ensuring authenticity. This makes Wellknown a valuable resource for developers seeking live A2A agents and their capabilities.

This data is a snapshot as of 2026-10-31.