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

Annotations already cover readOnly, idempotent, non-destructive and closed-world, so the bar is lower. The description still adds real behavior beyond them: default ordering (newest first), the per-enquiry fields returned (id, listing, latest message, unread count, replied flag), and the required OAuth scope `listings:read`.

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, front-loaded with the core purpose and ordering, then the entity shape, then the auth requirement and a concrete example. Nothing is padded, though the example sentence is the most expendable line.

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?

An output schema exists, so return values need not be explained, yet the description still sketches the enquiry shape. With only two optional, fully-documented parameters, the read-only annotation set, and the OAuth scope called out, an agent has everything needed to call this correctly.

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% and both parameters are documented in the schema, so the baseline is 3. The description adds no parameter meaning of its own — it never mentions the limit or the listingId filter, so an agent reading only the description would not know it can narrow results to one listing.

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 states a specific verb and resource ('Show the messages buyers have sent about the authenticated user's Cyclesite listings') plus ordering ('newest first') and the entity's shape. It implicitly separates enquiries from other message types, but never names the sibling get_my_messages, so the agent must still infer which of the two message tools to pick.

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?

Usage is conveyed by example ('any messages about my Trek?') and by the note that the seller can answer an enquiry by its id, which points toward respond_to_enquiry. There is no explicit when-not guidance and no sibling tool is named, so the routing decision is implied rather than stated.

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