MCP vs A2A: what AI agent teams need for tool access

At a glance

What this is: This is WorkOS’s comparison of MCP and A2A, showing that one protocol handles tool access while the other handles agent-to-agent collaboration.

Why it matters: It matters because IAM, PAM, and NHI teams now have to govern both execution paths and delegation paths when AI systems can reach tools and other agents.

👉 Read WorkOS's MCP vs A2A comparison for agentic systems

Context

MCP and A2A solve different identity problems. MCP governs how an agent reaches external tools and data sources, while A2A governs how agents discover one another, exchange tasks, and coordinate work.

For identity teams, that split matters because the control surface changes from tool permissions to delegation relationships. The question is no longer whether an AI system can act, but which identities it can reach, how those rights are scoped, and where accountability sits when multiple agents collaborate.

Key questions

Q: How should security teams govern AI systems that use both MCP and A2A?

A: They should govern the workflow as a delegation chain, not as two separate technical choices. MCP controls what tools an agent can reach, while A2A controls which peers it can delegate to. Security teams need identity registration, explicit scope, consent boundaries, and revocation for both layers so that collaboration cannot outrun access control.

Q: Why do MCP and A2A together create more identity risk than either one alone?

A: Because the risk is compounded across layers. A2A can broaden who receives work, and MCP can broaden what each recipient can touch. When those links are combined without strong scoping, the organisation gets a larger blast radius, more difficult revocation, and weaker accountability across the agent chain.

Q: What do IAM teams get wrong about agent-to-agent collaboration?

A: They often treat it as messaging infrastructure instead of delegated identity. If one agent can assign work to another, that handoff is a governance decision with access implications. IAM teams should require the same level of review for agent peers that they would require for privileged service accounts or other non-human identities.

Q: How can organisations decide whether to start with MCP, A2A, or both?

A: Start with the control surface that matches the problem. Use MCP when the main requirement is safe access to tools and data. Use A2A when the core need is coordination across specialised agents. Use both when orchestration and execution are both present, then govern the combined identity path as one system.

Technical breakdown

MCP tool manifests and JSON-RPC access to external systems

Model Context Protocol standardises agent-to-tool integration by advertising available tools through a server-side manifest and invoking them over JSON-RPC. That gives a model a predictable way to call a database query, file reader, or API without custom connectors for each system. The security value is in making tool access explicit, but the control model still depends on the server enforcing permissions, scoping, and session boundaries. Without those controls, standardisation reduces integration friction without reducing risk.

Practical implication: inventory MCP servers as NHI entry points and bind each advertised tool to explicit access policy.

A2A agent cards and peer-to-peer delegation

Agent-to-Agent Protocol is designed for horizontal collaboration. Agents publish capabilities in Agent Cards, then discover and delegate work to peers without sitting under a single master process. That makes A2A useful for distributed orchestration, but it also changes the trust model because the system now relies on identity, consent, and task handoff between autonomous peers. The protocol defines communication, not deep tool control, so delegation can expand faster than governance if the receiving agent is not tightly scoped.

Practical implication: treat A2A peers as delegated identities and require explicit trust and consent boundaries before task handoff.

Why MCP and A2A together create a broader identity surface

Used together, MCP and A2A separate orchestration from execution. One agent can delegate work through A2A, while each sub-agent uses MCP to reach the systems it needs. That creates a layered identity chain, where privilege is no longer held by one process but distributed across collaborating actors. For IAM and NHI governance, the key issue is not just authentication. It is whether each link in the chain has a defined purpose, a bounded tool set, and a revocation path when the delegation ends.

Practical implication: model agentic workflows as delegation chains and review both peer relationships and downstream tool entitlements.

Threat narrative

Attacker objective: The objective is to turn a legitimate agentic delegation chain into an over-broad execution path that reaches systems and data outside the intended scope.

1. Entry occurs when an agent is given legitimate MCP access to tools or an A2A relationship to peers, because the protocol itself assumes trusted enrollment and declared capability.
2. Escalation happens when a peer agent or delegated workflow gains broader context or tool reach than the original task required, allowing scope drift across the chain.
3. Impact emerges when chained agent actions reach sensitive systems, move data, or trigger business processes without a human review point that matches the speed of execution.

Breaches seen in the wild

• Moltbook AI agent keys breach — Moltbook breach exposed 1.5M AI agent keys.
• AI LLM hijack breach — attackers used stolen AWS access keys to hijack Anthropic LLM models on Bedrock.

Read our 52 NHI Breaches Analysis report for a comprehensive view of breaches impacting Non-Human Identities including AI Agents.

NHI Mgmt Group analysis

MCP and A2A are not competing identity models, they are different control planes. MCP is about bounded tool reach, while A2A is about delegated coordination between peers. The governance mistake is to treat either protocol as a complete agent identity strategy. Practitioners should read them as separate layers of one expanding identity surface.

Delegation is now an identity event, not just a workflow event. When an agent hands work to another agent through A2A, the security question is who is authorised to act, not just who can message whom. That means task routing, consent, and revocation belong in the identity conversation, not only the orchestration conversation. Practitioners should stop separating collaboration design from access governance.

Tool scoping alone does not solve agent governance. MCP can make tool access explicit, but it does not decide when an agent should be trusted to choose, sequence, or combine those tools in a business process. That gap becomes sharper when A2A is added, because one agent can delegate to another and amplify privilege across a chain. Practitioners should govern both entitlement and delegation.

Identity blast radius is the right concept for multi-protocol agent systems. The more an organisation combines MCP for execution and A2A for orchestration, the larger the consequence set when trust is misplaced. A mis-scoped peer relationship can lead to a mis-scoped tool session, then to a broader operational impact than either protocol would suggest in isolation. Practitioners should assess the full blast radius, not just the local connector.

Agentic AI governance will converge on lifecycle controls applied to non-human identities. Discovery, delegation, tool access, and offboarding all have to be tracked as one chain of ownership. The practical implication is that enterprises need a policy model that spans NHI registration, peer trust, and revocation, rather than isolated protocol-specific rules.

From our research:

• 33% of organisations report their AI agents have accessed inappropriate or sensitive data beyond their intended scope, according to AI Agents: The New Attack Surface report.
• Only 44% of organisations have implemented policies to govern AI agents, leaving a large share with documented behaviour but no formal control baseline.
• For a broader control model, see OWASP Agentic AI Top 10 for the risks that emerge once delegation and tool use combine.

What this signals

Identity blast radius: once orchestration and execution are split across different protocols, security teams need to think in terms of cumulative reach rather than isolated permissions. A permissive A2A relationship can turn into a permissive MCP session, and that chain is what governance has to measure.

With 33% of organisations already reporting agent access outside intended scope in AI Agents: The New Attack Surface report, the operational signal is clear: agentic programmes are already producing governance drift faster than review cycles are adapting.

For teams formalising this space, the useful next lens is the OWASP Agentic AI Top 10, because it frames tool misuse, delegation abuse, and identity boundaries as one connected risk surface.

For practitioners

• Map agentic delegation chains end to end Document which agents discover peers, which agents call tools, and where a human or policy gate can still interrupt the chain. Use that map to identify where one delegated task can expand into multiple downstream actions.
• Scope every MCP tool to a named business purpose Do not expose generic tool catalogs to agents without task boundaries. Limit each MCP server to the minimum tools required for the current workflow and tie access to a specific identity, session, or approval state.
• Treat Agent Cards as governance artifacts Review advertised capabilities the same way you would review service account privileges. If an agent can be discovered by others, its published scope, contact path, and delegation permissions should be approved and periodically recertified.
• Build revocation paths for both peers and tools Ensure that ending an A2A relationship also shuts off any MCP access that relationship enabled. If peer trust can continue after the task ends, the organisation has created standing privilege by another name.

Key takeaways

• MCP and A2A solve different problems, but together they create a broader identity surface that must be governed as one chain.
• Agent-to-agent delegation is an access decision, not just a messaging detail, and it can expand privilege faster than most IAM programmes expect.
• Enterprises should model tool reach, peer trust, and revocation together or risk creating standing privilege across collaborating agents.

Key terms

• Model Context Protocol: A standard that lets an AI model discover and call external tools and data sources in a predictable way. In identity terms, it turns tool access into a governed connection point, where the server must still enforce scope, permission, and session control for the calling agent.
• Agent-to-Agent Protocol: A protocol for letting agents discover peers, advertise capabilities, and hand work to one another. It matters for identity governance because the handoff is a delegation event, not just a message exchange, and delegated trust can expand the practical access surface very quickly.
• Agent Card: A published descriptor that tells other agents what an agent can do and how to contact it. It functions like a capability statement for delegated machine identities, so security teams should treat it as a governance artifact and review it for scope, trust, and offboarding implications.
• Identity blast radius: The total set of systems, data, and actions that can be reached when one identity chain is mis-scoped. For agentic systems, blast radius can grow across both peer delegation and downstream tool access, so the control question becomes how far one compromised or over-trusted relationship can travel.

Deepen your knowledge

MCP, A2A, and agentic identity governance are core topics in our NHI Foundation Level course, the industry's only accredited NHI security programme. If your team is starting to formalise agent access and delegation, it is a practical place to build shared language and controls.

This post draws on content published by WorkOS: MCP vs. A2A: Which AI agent protocol should you use? Read the original.