Call a worker from anything.
Four inbound call shapes, one outbound flow, and ten things people actually build. Everything below runs behind your guardrails — opt-in exposure, bearer auth, kill-switch, and audit.
Four ways to call a worker
The bridge is bound to localhost and reachable externally only through a tunnel you start in Settings → A2A. Pick the shape that fits the caller.
Discover
Public Agent Card — capability discovery, no auth.
# Discover (public, no auth) → Agent Card listing your exposed workers as "skills"
GET https://<host>/.well-known/agent.jsonSync
Run to completion; the cited answer comes back on the same request.
# (1) SYNC — run to completion, answer on the same request
POST https://<host>/a2a/v1/message/send
Authorization: Bearer <a2a token>
{ "message": { "role": "user",
"parts": [ { "kind": "text", "text": "Research the EU market for X, with sources." } ] },
"skillId": "<persona uuid, optional — defaults to Theodor>" }
→ { "message": { "role": "agent",
"parts": [ { "kind": "text", "text": "…cited summary…" } ] },
"conversationId": "…" }Stream
SSE status events for long tasks — see tools fire as they run.
# (2) STREAMING — Server-Sent Events for long tasks
POST https://<host>/a2a/v1/message/stream (same body + Bearer)
event: {"type":"status","state":"working","tool":"deep_research"}
event: {"type":"status","state":"completed","message":{ … }}Push + lifecycle
Fire-and-forget with a webhook callback; poll or cancel by task id.
# (3) ASYNC PUSH — fire-and-forget; result POSTed to your webhook later
POST …/message/send
body adds: "pushNotification": { "url": "https://you/cb", "token": "…" }
→ 202 { "taskId": "…" }
# (4) LIFECYCLE — poll or cancel a push-mode task by id
POST …/a2a/v1/tasks/get { "taskId": "…" }
→ { "status": "working|completed|failed|canceled", "message": …, "conversationId": "…" }
POST …/a2a/v1/tasks/cancel { "taskId": "…" } → { "status": "canceling" }📤 The other direction — a worker hires an agent
Theodor delegates a sub-task to an outside specialist, fetches what it built, and continues the workflow — inside one org chart, one delegation tree, one audit log. Token resolution happens server-side.
# A worker hires another agent — URL + token resolved server-side, never in-context
a2a_delegate(agent="OpenHands", task="implement the CSV export and add a test")
# CLI agents run via shell + fs; the worker fetches the artifact and continues
shell: openhands --task "…" --dir ./work/feature-x → fs_read ./work/feature-x/export.rs