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

Annotations already declare readOnlyHint=false, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds value beyond that: the error behavior when the ZIP is already served, and the asynchronous side effect that Fold emails the user if service starts there. It does not describe the response shape, but with no output schema that is a minor gap.

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 sentences, no filler, and the core action plus its scoping rule are front-loaded before the error case and consent note. Every sentence carries distinct 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 3-parameter write tool with no output schema, the description covers the action, the guard condition, the error case, the downstream email side effect, and a consent policy. Only the handling of the optional firstName and any pagination/response detail are unspecified, which is acceptable at this complexity.

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 email, zipCode, and firstName are already documented in the schema. The description reinforces the ZIP constraint ('5-digit US ZIP' semantics appear in the schema) and adds a consent requirement for email, but contributes no syntax or format detail the schema lacks. Baseline 3 applies.

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 ('Adds an email address to Fold's waitlist') with an explicit scope constraint ('for a ZIP code Fold doesn't serve yet'). That scope constraint is exactly what separates it from the other ZIP/service siblings, so an agent can identify it 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 a clear positive condition ('Only for unserved ZIPs') and spells out the failure mode for the wrong condition (served ZIPs return an error). It also adds a consent rule ('Use the person's own email with their permission'). It stops short of naming check_service_zip as the prerequisite lookup, so the alternative is implied rather than named.

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