# Agent Identity and Discovery vs Agent2Agent Protocol

The map lists them as complementary: sites and agents commonly implement both. They answer different questions: Agent Identity and Discovery is a step 1 (Discover) standard, Agent2Agent Protocol step 6 (Coordinate), so they are not substitutes.

[1 Discover](/category/discover/) [Agent Identity and Discovery](/protocols/aid/) · [6 Coordinate](/category/coordinate/) [Agent2Agent Protocol](/protocols/a2a/)

|  | [Agent Identity and Discovery](/protocols/aid/) AID | [Agent2Agent Protocol](/protocols/a2a/) A2A |
| --- | --- | --- |
| Lifecycle step | 1 Discover: What is here, and where? | 6 Coordinate: Talk to another agent |
| Answers | Given a domain, where is the agent and which protocol should I speak, with cryptographic proof the endpoint controls the matching key? | How do two independent agents, built on different frameworks, discover each other and delegate a task to completion? |
| Governed by | Agent Community open-source project; editor listed as 'Agent Community'; no formal standards body, though the spec discusses composing with IETF-track work (RFC 9421, RFC 7638, RFC 9728, RFC 8414) | Linux Foundation; Technical Steering Committee with AWS, Cisco, Google, IBM Research, Microsoft, Salesforce, SAP, ServiceNow |
| Status (issuer's words) | Current normative specification | Stable, v1.0.0 |
| Phase | living | stable |
| Version | v2.1.0 (aid2 wire format; aid1 legacy) (2026-06-01) | 1.0.1 (2026-05-28) |
| Form / transport | DNS record | endpoint |
| Found at | _agent.<domain> (DNS TXT); /.well-known/agent (HTTP fallback) | /.well-known/agent-card.json |
| Adoption | observed | claimed — Linux Foundation |
| Evidence | 3 verified | 4 verified, 1 reported |
| Primary use case | Let agents discover my API or service | Let agents talk to other agents |
| Last verified | 2026-10-19 (current) | 2026-10-19 (current) |
| Specification | [https://raw.githubusercontent.com/agentcommunity/agent-identity-discovery/main/packages/docs/specification.md](https://raw.githubusercontent.com/agentcommunity/agent-identity-discovery/main/packages/docs/specification.md) | [https://a2a-protocol.org/latest/specification/](https://a2a-protocol.org/latest/specification/) |

## When to use which

- Choose Agent Identity and Discovery when your question is “Given a domain, where is the agent and which protocol should I speak, with cryptographic proof the endpoint controls the matching key?” and you accept its maturity: phase living, adoption observed.
- Choose Agent2Agent Protocol when your question is “How do two independent agents, built on different frameworks, discover each other and delegate a task to completion?” and you accept its maturity: phase stable, adoption claimed (Linux Foundation).

Guidance is derived from the two records (question, phase, adoption, prerequisites, pairings), not from opinion. Each record's page carries its numbered references.

## Read the full articles

- [Agent Identity and Discovery](/protocols/aid/): Given a domain, where is the agent and which protocol should I speak, with cryptographic proof the endpoint controls the matching key?
- [Agent2Agent Protocol](/protocols/a2a/): How do two independent agents, built on different frameworks, discover each other and delegate a task to completion?

Ask the MCP server to compare any two: the compare-protocols prompt, or get on both ids. [Connect](/connect/).

[aid.json](/data/protocols/aid.json) · [a2a.json](/data/protocols/a2a.json) · [Markdown](/compare/aid-vs-a2a/index.md)