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

Annotations already declare readOnlyHint, idempotentHint, and non-destructive behavior, so the description only needs to add context beyond those. It adds a current-month rollup and which metrics are covered, but does not describe any caveats, such as whether data is near-real-time, delayed, or how the outputs are shaped. This is adequate but not rich.

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?

One concise, front-loaded sentence states the resource, time scope, and outputs. Every word adds value, and the structure efficiently communicates the necessary 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 zero-parameter read-only rollup tool, the description is complete: it specifies the time window, the item being retrieved, and the metrics contained in the result. The annotations cover the safety profile, so no further context is necessary for an agent to invoke this tool appropriately.

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?

There are zero parameters, so the description cannot add parameter meaning. The baseline for zero-param tools is 4; the description simply confirms the lack of inputs by being a standalone retrieval tool. Nothing about parameters needs explanation.

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 ('get') with a concrete resource ('current-month usage rollup') and enumerates the components (calls placed, minutes, active numbers, spend). This clearly differentiates from sibling tools that work with individual calls or numbers.

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 'current-month' qualifier and aggregate focus imply usage is for cumulative monthly statistics rather than for listing calls or performing actions. It does not explicitly name alternatives or exclusions, but context is clear enough for an agent to choose it over call-listing or SMS tools.

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