EXPLAINER

Agent Protocol Landscape (MCP, A2A and Others)

conceptfreshness: volatilesources not yet verified

Several protocols are emerging for agent interoperability. They operate at different layers: tools and context, agent-to-agent messaging, discovery and payments/identity.

Short answer: Think in layers: tool/context access (MCP), agent-to-agent collaboration (A2A), agent discovery/identity, and application-level UI/streaming conventions. The landscape moves fast — treat any list of protocols as a snapshot to re-verify.

What is it?

Agents need ways to connect to tools, to each other and to users. Different protocols are being proposed for different jobs, much like the web has separate standards for transport, identity and page content. Knowing which layer each solves keeps you from comparing apples to oranges.

Also known as: agent protocols, agent interoperability standards, MCP vs A2A vs ACP, agent communication protocols, agent standards, AI agent protocol stack.

Technical definition

Layer view: (1) model ↔ tools/data — function calling APIs and What is MCP (Model Context Protocol)?; (2) agent ↔ agent — A2A (Agent2Agent) Protocol and framework-specific messaging; (3) identity and authorisation — OAuth/OIDC patterns applied to agents; (4) agent ↔ user interface — streaming and UI-event conventions that vary by vendor; (5) commerce/payment and discovery proposals that are early and unsettled. Standards bodies, governance and adoption change rapidly; this entry deliberately names no "winner".

Entity type: concept · Freshness class: volatile.

When should I use it?

Use as a map before choosing integration standards.

Implementation patterns

  • Start at layer 1; add layer 2 only when independent agents must interoperate.
  • Isolate protocol adapters so you can swap them.
  • Pin protocol versions and test conformance.

Technologies and frameworks

Commonly associated: MCP, A2A, OAuth 2.x / OIDC, OpenAPI. Names are examples of what exists, not recommendations, and projects change quickly.

Practical guide

  1. List your agents/tools and owners.
  2. Identify trust boundaries.
  3. Pick the lowest layer that solves the problem.
  4. Check current specs and SDK support.
  5. Re-review quarterly.

Common failure modes

  • Betting on a protocol because of hype rather than ecosystem fit.
  • Building bespoke wire formats where a standard exists.
  • Assuming protocol support implies security.

Troubleshooting

  • Unsure what you need — Write down who owns each agent/tool and whether they are in the same trust domain.

Contrasted with

Questions this page answers

  • What agent protocols exist?
  • How do MCP and A2A fit together?
  • Which agent protocol should I use?
  • Are there standards for agent identity?

Typical goals: map the agent protocol ecosystem; decide which protocol layer you need.

Sources and verification

Status: not independently verified. This entry was authored on 2026-10-06 from general technical knowledge, without live checking of the sources below. Treat every source as a lead to confirm (identifier, title, authorship, current version) before publication or citation.

Freshness class: volatile — Products, versions, protocols, benchmarks, leaderboards, regulations and dates. Verify against the primary source before relying on specifics; re-review every 3 months.

Time-sensitive claims to verify before relying on them:

  • Which protocols exist, their governance, versions and adoption.
  • Any statement about protocol convergence or merger.

Canonical sources (unverified leads):

  • MCP specification — modelcontextprotocol.io
  • A2A specification — a2a-protocol.org (verify)
  • Current comparisons by standards bodies or vendors (identify at time of writing) — locator to be identified