spec.capabilities

Declares which protocol-level capabilities the agent supports. All three fields are required so the schema makes the agent's contract explicit - a runtime should never need to guess whether streaming is on.

These are the A2A AgentCard capability flags - what a caller reads off the agent's card before connecting. See A2A & the Agent Card for what each flag means to a client.

spec:
  capabilities:
    streaming: true
    pushNotifications: true
    stateTransitionHistory: true

streaming

• Type: boolean
• Required: yes

Whether the agent can stream incremental responses (typically token-by-token) back to the caller, instead of returning a single buffered result.

pushNotifications

• Type: boolean
• Required: yes

Whether the agent can push notifications about state changes - useful for long-running tasks where the caller subscribes and is informed when something happens.

stateTransitionHistory

• Type: boolean
• Required: yes

Whether the agent retains a record of state transitions over the course of a task. When true, callers can replay or audit how the agent reached its final state.

A note on defaults

There are no defaults - every value must be explicitly true or false. This is intentional: a manifest that elides streaming would leave runtimes and clients unsure what to negotiate. Making the field required forces the author to think about it.