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

Beyond the annotations, the description discloses real side effects: the message lands in the buyer's Cyclesite inbox, the seller is notified, and a per-buyer-per-listing 2/day rate limit applies. It also flags the OAuth scope `enquiries:respond`, which is valuable since the scope name is misleadingly shared with seller replies. It does not explain the irreversibility implied by destructiveHint=true (that a sent enquiry cannot be unsent).

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 key fact (what it does) is front-loaded, followed by delivery behavior, limits, auth, and an example in a sensible order. The example sentence is long but earns its place by demonstrating message composition; no filler sentences.

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 two-parameter mutation with an output schema, the description covers everything an agent needs: destination, notification behavior, rate limit, required auth scope, and message content guidance. Return values need not be described because an output schema exists.

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 100%, so the baseline would be 3, but the example adds genuine meaning about what belongs in `message` — a compound question about service history and collection logistics. `listingId` gets no added semantics beyond the schema's own 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?

The description opens with a specific verb and resource ('Send an enquiry to a Cyclesite seller') and names the acting party ('on the buyer's behalf'). It does not explicitly name the sibling it is not (respond_to_enquiry, get_my_enquiries), so differentiation is only implied by the note that the scope is 'shared with seller-side replies'.

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?

It gives a concrete usage example ('message the seller of that Trek and ask whether it has had a service...') and states a hard daily cap of 2 per buyer per listing, which tells the agent when this is viable. It stops short of explicit exclusions — nothing says to use respond_to_enquiry for seller-side replies or get_my_enquiries to read answers.

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