What is A2A, and how does Loomcoding use it?

What it is

A2A is an open protocol for agents to exchange work as tasks. Loomcoding uses it as the base for talking to other agents, instead of a protocol of its own. Where Loomcoding adds a rule or a state of its own, this page says so.

What it is for

• Running subagents as A2A tasks.
• Using remote agents that someone else runs.
• Sharing your local agents with other clients, if you turn that on.

How

1. Set the A2A role in loomcoding.toml. It is off by default.
2. Approve each remote agent in /agents.
3. Inspect cards, tasks and exchanges with /a2a.

Example

[a2a]
role = "consume"   # use remote agents that you have approved

Roles and statuses

Role ([a2a] role)	What it does
off	Default. No A2A client and no listener.
consume	Delegates to remote agents that you have already approved.
serve	Exposes your local agents to other clients. It needs an explicit setting and authentication, kept in ~/.loomcoding/runtime.toml.
both	Does both: consume and serve.

The A2A protocol defines eight task states: submitted, working, input-required, auth-required, completed, failed, canceled and rejected.

Subagents have a richer state of their own, which Loomcoding shows in the flock. Each of those states is projected to one A2A state:

Loomcoding phase (own)	A2A state shown to other agents
Queued, Starting	submitted
Streaming, Reasoning, ToolRunning, AwaitingPermission, Working, Stalled, Unknown	working
AwaitingParentInput	input-required
AwaitingCredentials	auth-required
SettledOk	completed
SettledErr, Lost	failed
Rejected	rejected
Canceled	canceled

Loomcoding's own phases and rules, not defined by A2A:

• The phases Stalled and Lost, which come from the progress watch on subagents.
• The delegation modes off, on_request and proactive.
• The routing setting, which chooses an agent by itself. A2A does not say how to choose an agent. The routing is off by default.
• The ODD phases in the header, see ODD.

Remote agents

A remote agent is a profile file with transport: a2a-remote and the address of the agent. Loomcoding downloads its card, which describes what the agent can do.

1. Open /agents and approve the remote agent. Nothing runs before you approve it.
2. Use /refresh-agents to download the cards again.
3. A remote agent can ask you a question while it works. The phase for that is "awaiting parent input".

Settings and defaults

Name	Default	Requires restart
[a2a] role	off	Yes
[a2a] request_timeout_secs	30 seconds	Yes
[a2a] card_refresh_secs	3600 seconds. 0 turns the refresh off. The minimum is 60.	Yes
[a2a] max_card_bytes	65536 bytes (64 KiB)	Yes
[a2a] max_result_bytes	262144 bytes (256 KiB)	Yes

Loom reads the [a2a] section when it creates the agent. Restart Loom after you edit it.

For the status of each A2A task in the project, see the A2A roadmap.

Next steps

• Agents, subagents and jobs
• Permissions