# About — Agent Cards Explained

> A reference layer for the A2A Agent Card spec, built and maintained by the AgentsBooks team.

## Why this site exists

The A2A v1.0 specification is excellent reference material but expects context. Agent Cards are the load-bearing artefact of A2A — the JSON document at the well-known URL — and the operational decisions around them (signing, publishing, key rotation, comparison to OpenAPI / robots.txt / model cards / MCP descriptors) are scattered across vendor blogs, IETF drafts, regulator publications, and academic papers. This satellite consolidates the operational knowledge into one place.

## Who it is for

- **Agent developers** deciding how to expose A2A agents to outside callers.
- **Marketplace operators** building or maintaining catalogs of A2A agents.
- **Security architects** reviewing A2A deployments.

## The framing

> "A2A provides the definitive common language for agent interoperability in a world where agents are built using diverse frameworks and by different vendors." — A2A Protocol — Specification v1.0 (in force; accessed 2026-05-08)

> "Agents can advertise their capabilities using an 'Agent Card' in JSON format, allowing the client agent to identify the best agent that can perform a task and leverage A2A to communicate with the remote agent." — Google Developers — Announcing the A2A Protocol

## Eight primitives

Identity · Brain · Heart · Memory · Control · Knowledge · Friends · Shares. See https://agentsbooks.com/anatomy. Agent Cards live in the *Friends* primitive — agent-to-agent — and reinforce Identity, Heart, and Control.

## Built by AgentsBooks

This is one of a small, growing family of authority properties published by AgentsBooks — pillar essays, comparison matrices, ROI calculators, glossaries, and research indexes. They share a vocabulary, an editorial voice, and a single primary CTA: try AgentsBooks free.

## Editorial discipline

Every claim is anchored to a canonical primary source. Methodology and full bibliography on `/pages/methodology.md`; audit trail in `raw/research-notes.md` in the source repository.

## Refresh discipline

Default: bi-annual full review. Trigger refreshes on A2A spec revision, IETF AAuth RFC progression, NIST CAISI publication, Microsoft Entra Agent ID major update, new Linux Foundation founding-member announcement, or major marketplace launch.

## CTAs

- Primary: Try AgentsBooks Free → https://agentsbooks.com/login?returnTo=/onboarding
- Secondary: A2A & Orchestration pillar → https://agentsbooks.com/blog/a2a-protocol-explained

*Updated 2026-05-08.*