MCP vs A2A: agent-protocol comparison
MCP and A2A are not competitors. They standardise different layers of the agent stack: MCP standardises how a single agent discovers and calls external tools (model-to-tool); A2A standardises how one agent delegates work to another agent across organisational or vendor boundaries (agent-to-agent). Most enterprise agent deployments will eventually use both — MCP for the local tool surface, A2A for the cross-vendor coordination surface. This comparison exists because procurement teams and architecture leads frequently treat them as alternatives in early conversations. They are not. Understanding which protocol governs which boundary is the first decision in a 2026 multi-vendor agent architecture.
Who this is for
- · Architecture leads designing 2026 enterprise agent integrations
- · Platform engineers evaluating tool-server and inter-agent protocol layers
- · Procurement teams evaluating vendor protocol-portability claims
Model Context Protocol (MCP) ↗
Open standard for agent-to-tool integration. Originated at Anthropic; growing third-party server ecosystem. Defines how an LLM-based agent discovers tools, structures tool-call parameters, and consumes tool responses.
Agent-to-Agent Protocol (A2A) ↗
Open standard for agent-to-agent delegation across vendor and infrastructure boundaries. Originated at Google; multi-vendor working groups participating. Defines how one agent advertises capabilities and another delegates tasks.
Feature matrix
| Dimension | Model Context Protocol (MCP) | Agent-to-Agent Protocol (A2A) |
|---|---|---|
| Layer of the stacksource ↗ | Model-to-tool — single agent discovering and calling external tools | Agent-to-agent — one agent delegating to another agent across boundaries |
| Originatorsource ↗ | Anthropic (open-sourced 2024) | Google (open-sourced 2025) |
| Adoption maturity (Q2 2026)source ↗ | Production-grade; broad SDK support across vendors; growing third-party server ecosystem | Early-adoption; multi-vendor working groups; not yet at deployment-grade stability for production-critical workloads |
| Native vendor supportsource ↗ | Anthropic Claude (native); OpenAI (added 2025); Google Gemini (added 2025); Cursor; Cline; Continue | Google Vertex (originator); Anthropic; partner ecosystem expanding |
| Transportsource ↗ | JSON-RPC over stdio (local), SSE/HTTP (remote) | HTTP / gRPC; capability-card discovery |
| Authentication / authorisationsource ↗ | OAuth 2.0 + scope-based permissions; per-tool authorisation | OAuth 2.0 + capability-card declarations; agent identity verification |
| Use case the protocol is forsource ↗ | Agent needs to read a database, send an email, call an internal API | Agent needs to delegate a sub-task to another vendor's agent that has different capabilities or different data access |
| Governance overlaysource ↗ | Permission scopes per tool; audit log per invocation | Capability cards declare action surface + auth requirements; provenance tagging on inter-agent calls |
| Best for broker-mediated multi-agentsource ↗ | Yes — the broker uses MCP to dispatch tool calls | Yes — the broker uses A2A to route inter-agent messages |
| Replaces what existed beforesource ↗ | Vendor-specific function-calling formats (OpenAI tools API, vendor-specific connector frameworks) | Vendor-specific delegation APIs (custom inter-vendor agent integrations) |
When to choose which
MCP is the right protocol for any enterprise agent that needs tool integration with internal systems. As of Q2 2026 it is at production-grade stability. Use MCP for the local tool surface (databases, APIs, files, internal services) regardless of which foundation-model vendor the deployment uses.
A2A is the right protocol for cross-vendor or cross-organisation agent delegation, but production-grade stability is still maturing. As of Q2 2026, treat A2A as a 12-18 month investment for enterprises designing multi-vendor agent architectures, not a Q2 2026 production primitive. Use it where the deployment needs vendor-portable agent-to-agent coordination.