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

Annotations already mark this as destructive and non-read-only, but the description adds critical behavioral context: messages are delivered immediately, cannot be unsent, the recipient sees they were sent through an assistant, and there is a 3-message rate limit until a reply. This goes well beyond the annotations.

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?

Four sentences, each earning its place: usage, parameter routing, delivery/visibility/confirmation behavior, and rate limit. The most important usage guidance is front-loaded.

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?

The description covers when to use, how to target recipients, irreversible delivery, assistant disclosure, confirmation requirement, and rate limiting. With an output schema present, return values need not be explained, so the definition is complete.

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. The description adds meaning by explaining the routing choice ('Give listing_id to reach that listing's owner, or to_user_id to reply to someone'), clarifying the purpose of to_user_id beyond its terse schema description.

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 another TraydStar member') and distinguishes the use case from formal proposals by noting 'before proposing a trade'. An agent can identify this as the direct messaging tool without opening the schema.

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?

Gives clear conditions for use ('when the user wants to message another TraydStar member') and explains how to choose between listing_id and to_user_id. However, it does not explicitly name alternative sibling tools or state when not to use this tool.

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