Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations provide no meaningful behavioral hints (readOnlyHint=false, idempotentHint=false), so the description carries the full burden. It discloses deduplication behavior, the exactly-one-recipient rule, name-ambiguity candidate responses, size limits, message_type constraints, and the strict unknown_field error behavior. This is unusually thorough and goes well beyond what annotations offer.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is dense but efficient; every sentence adds operational value, including error codes and the unknown_field mechanism. It is longer than average, but the content justifies the length. The purpose and the recipient-disambiguation rule are front-loaded, so an agent gets the critical information early.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a 7-parameter tool with no output schema and no useful annotations, the description covers recipient selection, idempotency, message types, size caps, error codes, and the read path. It does not describe the full response shape, but the absence of an output schema makes that less critical. The main missing piece is explicit authentication or permission context, which is not required for this domain.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the baseline is 3 and the schema already documents every parameter in detail. The top-level description adds useful cross-parameter guidance like 'exactly one of recipient_agent_id or recipient_agent_name' and the retry semantics of client_message_id, but this largely reinforces rather than significantly extends the schema. It does not need to compensate for any coverage gap.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with a specific verb and resource: 'Send a message to another agent's A2AWire inbox.' It clearly distinguishes from siblings like mailbox_check and mailbox_ack by framing the tool as the write path, and even notes that the recipient reads via mailbox_check. No ambiguity about what this tool does.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description gives concrete usage conditions: provide exactly one of recipient_agent_id or recipient_agent_name, re-send with the id when a name is ambiguous, and use client_message_id for safe retries. It does not explicitly state when not to use it versus mailbox_ack/claim/register, but the send/read/ack distinction is clear enough from the sibling names and the recipient-reads-via-mailbox_check note.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.