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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds useful context beyond that by specifying the operation is authenticated and tied to the supplied X-API-Key, and confirms a read-only 'retrieve' behavior. No contradictions.

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?

A single, front-loaded sentence with no filler. Every phrase ('Retrieve', 'authenticated API usage', 'current plan limits', 'supplied X-API-Key') carries meaningful information for a zero-parameter tool.

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 zero-parameter read-only status/usage tool, the description is largely complete: it identifies the operation, resource, and authentication context. It does not describe the exact response shape, but the simple nature of the tool and the safety profile from annotations make that a minor gap.

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?

The tool has zero parameters and schema coverage is 100%, so the baseline is 4. The description usefully clarifies that the X-API-Key is the authentication context rather than an input parameter, which prevents an agent from hunting for a parameter that does not exist.

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 ('Retrieve') and names a precise resource: authenticated API usage and current plan limits for the X-API-Key. This clearly differentiates it from sibling tools like calculate_shipping or get_vehicle, all of which concern different domains.

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?

The description implies a clear usage context: whenever authenticated API usage or current plan limits are needed. Although it does not explicitly name alternatives or exclusions, the sibling tools are so unrelated that an agent can confidently choose this tool without further guidance.

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