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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds real behavioral detail beyond that: the 31-day maximum range and the default window (start of current month through now), which an agent needs to size requests correctly.

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?

Two sentences, front-loaded with the resource and scope, then constraints; the trailing API endpoint reference is compact and unambiguous. No filler.

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 parameterless-required read-only list with no output schema, the description helpfully enumerates the shape of each returned charge entry and the default time window, which is exactly the information an agent would otherwise miss given the absent output schema.

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 carry their own descriptions including format, defaults, and the 31-day rule, so the schema does the heavy lifting. The description restates the same range/default information, adding no syntax or semantic detail beyond the schema.

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 ('List billable usage for a period') and enumerates the returned fields (product code, label, region, time span, hours, size_gb for volumes). It is unmistakably distinct from sibling list tools such as civo_list_instances or civo_get_quota, though it does not explicitly name an alternative.

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 implied by the resource name and the returned-field list, and the 31-day range constraint gives practical context, but there is no explicit when-to-use/when-not guidance or pointer to alternatives like civo_get_quota.

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