How to create a remote agent exposed via A2A in Foundry?

[buzahid]

In the Foundry portal, I created and published an agent MyAgent:

I created another agent a2a-test to try and connect to this agent using the custom Agent2agent tool, however I'm seeing an error ErrorFailed to fetch agent card: Response status code does not indicate success: 401 (PermissionDenied).

What is the correct way to use the A2A protocol with agents created in Foundry?

[leestott]

Hi @buzahid

Why you are seeing the 401 (PermissionDenied)

Agents created and published in the Foundry portal (like MyAgent) are not exposed as public A2A servers. The “Activity Protocol endpoint” and “Responses API endpoint” shown in the Foundry UI are internal, authenticated endpoints intended for Microsoft 365 Copilot and Foundry‑managed runtimes. They do not expose a public A2A agent card endpoint.

When your a2a-test agent tries to use the Agent2Agent (A2A) tool to fetch the agent card for a Foundry‑hosted agent, the request fails with 401 (PermissionDenied) because:

• The endpoint is not a public A2A endpoint
• It requires Foundry/M365‑scoped authentication
• Anonymous or external A2A card resolution is not supported for Foundry‑hosted agents

This behavior is expected with the current Foundry architecture.

What is supported today

1. Foundry agent calling an external A2A agent (supported)

The A2A tool in Foundry is designed for this pattern:

• A Foundry agent acts as the A2A client
• The remote agent is hosted externally (for example, Azure Container Apps, Functions, VM, or another service)
• The remote agent implements the A2A protocol and exposes a public agent card endpoint
• That external agent is registered in Foundry as an A2A connection
• Authentication is configured (shared identity or delegated identity)

Official docs:
https://learn.microsoft.com/azure/ai-foundry/agents/how-to/tools/agent-to-agent
https://learn.microsoft.com/azure/ai-foundry/agents/concepts/agent-to-agent-authentication

2. Foundry agent to Foundry agent composition (do NOT use A2A)

If both agents live inside Foundry, the correct approach is:

• Connected Agents
• Multi‑Agent Workflows

These are native Foundry composition mechanisms. A2A is not used for Foundry‑to‑Foundry agent calls.

Reference:
https://techcommunity.microsoft.com/blog/azure-ai-foundry-blog/building-a-digital-workforce-with-multi-agents-in-azure-ai-foundry-agent-service/4414671

What is NOT supported

• Using A2A to call a Foundry‑hosted agent from another Foundry‑hosted agent
• Treating a Foundry‑published agent as a public A2A server
• Fetching an A2A agent card from the Foundry “Activity Protocol endpoint”

Key Considerations

• Foundry agents are A2A consumers, not A2A servers
• A2A is for Foundry → external agents
• Foundry → Foundry agent orchestration should use Connected Agents or Workflows
• A 401 PermissionDenied when fetching an agent card from a Foundry agent endpoint is expected

Hope this clarifies your question.

[hhoeksel]

Hi Lee,

Does this also apply to the agents in the new foundry? As far as I am aware the connected agents feature was removed.

I am currently trying (and strugling!) doing the same thing and was also looking at the agent 2 agent connector.

Best regards, Hans

[finleysg]

@leestott I am also wondering about the status of Connected Agents. The official recommendation (https://learn.microsoft.com/en-us/azure/foundry/agents/how-to/migrate?tabs=python#agent-tool-availability) is two alternatives, depending on the pattern:

Workflows — for multi-agent orchestration within Foundry (Agent B takes full ownership of the thread from the point of handoff)
A2A tool — for a Foundry agent calling an external agent endpoint (Agent A stays in control, gets the answer back)

I have in mind an agent orchestrator that hands off work to specialists and synthesizes the results of a user. It doesn't appear to me that Foundry will support this going forward. So when you suggest connected agents as an alternative to A2A, isn't that a dead end?

[mdmddan]

Hi @leestott, joining this thread because I'm hitting the same 401 as @buzahid
on the same scenario.

I have an existing multi-agent system (orchestrator + 8 specialists) running
in classic Foundry today using Connected Agents, that needs to migrate to
new Foundry.

There's a contradiction between your reply and the official migration docs
that I need help reconciling:

• Your reply (Feb 11) suggests Connected Agents as the alternative for
  Foundry-to-Foundry orchestration.
• The official "Agent tool availability" section in the migration guide
  (https://learn.microsoft.com/en-us/azure/foundry/agents/how-to/migrate)
  shows Connected Agents is NOT available in new Foundry, replaced by
  Workflows and A2A.
• @hhoeksel and @finleysg both raised this in followups that haven't
  been answered.

Concrete question: For an orchestrator that dynamically delegates to
specialists by intent and synthesizes results (Agent A keeps control,
Workflow handoff is not the right pattern), what is the supported path
in new Foundry today? Is the only option to wrap each Foundry agent as
an external A2A endpoint?

Asking to commit to a real migration plan. Thanks.

[MiguelGomez2401]

Commenting for visibility. I am working with partners on building an agent, and we want to have a caller/orchestrator agent that dynamically calls its sub agents based on what is needed from the user. End goal is to expose this through M365 and Teams.

We initially thought of using "Connected Agents", but this feature will be deprecated, and Workflows does not seem to solve this problem as we would have to "build" the logic into the if/else's.

I've also tried enabling A2A through the REST API script given here, but this approach doesn't seem to work.

I've tried using Microsoft Agent Framework and this works, however this brings in two additional things I am not sure about:

1. We would need to host that agent somewhere as it is not built on Foundry
2. Do we need to use M365 Agent Toolkit to expose it to M365/Teams?

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