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

Annotations already mark it read-only, idempotent, and non-destructive. The description adds useful context beyond annotations: the tool requires authentication and returns time-series buckets with named fields such as subscriptionUsed, extraUsed, totalUsed, and extraPurchased. There is no contradiction with annotations.

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 description is compact and front-loaded with the core purpose, then summarizes parameters, return structure, and the alternative tool. There is slight redundancy between 'for analyzing usage patterns' and 'Use for trend analysis and spotting usage spikes,' but overall every part is useful.

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?

Since there is no output schema, the description compensates by naming the return shape (time-series buckets for credits and exportRows with the relevant fields). It also covers authorization, default behavior, and the related sibling tool. Nothing critical is missing for this read-only usage-history tool.

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 75%, and the schema already documents range, granularity, and feedback. The description mostly repeats the range/granularity enums and defaults without adding new meaning, and it omits the feedback and _requestId parameters entirely. This falls at the baseline for schema-covered parameters.

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 names a specific action and resource: get the authenticated user's credits and export-rows usage over time. It clearly frames this as a trend-analysis tool and explicitly contrasts it with getAccountDetails, which handles current remaining balances.

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 says when to use the tool ('Use for trend analysis and spotting usage spikes') and when not to use it ('For current remaining balances, use getAccountDetails instead'). It also documents the range and granularity choices so the agent can decide appropriate calls.

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