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

With no annotations, the description carries the full burden and does so well: including `proposal` updates the bid and 'hands the turn to the other side', omitted fields keep their value, and the counterparty can then accept it. It doesn't disclose auth/rate-limit behavior, but the mutation and turn-passing semantics are the key traits an agent needs.

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?

Three front-loaded sentences with zero filler: the core action first, the counter-proposal mechanics second, and the A2A routing advice last. Every clause carries usable information.

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 messaging tool with a nested proposal object and no output schema, the description covers the mutation effect, turn handoff, and field-omission rule. Return-shape details are absent but the response semantics ('hands the turn to the other side') are conveyed, which is what an agent needs to proceed.

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 coverage is 50%, so the description must compensate, and it does for the most complex parameter: `proposal` is unpacked as {amount?+currency?, terms?} with the rule that omitted fields retain their value and price/terms can be set independently. body and bid_id are self-evident; the api_key warning lives in the schema.

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?

States a specific verb and resource ('Message the other party on a bid') and explains the counter-proposal capability. It is clearly distinguishable from accept_bid/reject_bid/place_bid by its messaging purpose, though it never explicitly names a sibling to contrast against.

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?

Provides a clear alternative and condition: 'For long negotiations prefer A2A directly (counterparty.agent_card_url on get_bid) and mirror the final terms here.' This tells the agent when to route elsewhere, but gives no guidance on when to prefer send_message over accept_bid or reject_bid for finalizing a deal.

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