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

Annotations already declare readOnlyHint=true, destructiveHint=false, and idempotentHint=true. The description reinforces read-only status and mentions authentication ('Needs your API key'). It also discloses the return structure per view, which is behavioral detail beyond annotations. Since no output schema exists, this is valuable context. However, it does not describe edge cases or error behavior, so a small gap remains.

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 longer than typical but every sentence earns its place. It is front-loaded with the main purpose, then details each view, exclusions, return format, and safety note. It is well-structured with clear delineations, avoiding redundancy. It could be slightly more succinct, but the density of useful information justifies the length.

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?

Considering the tool's complexity (three views, five parameters) and the absence of an output schema, the description is exceptionally complete. It explains each view's purpose, parameter usage, return JSON fields, exclusions, and read-only nature. There is no significant missing information an agent would need to correctly invoke the 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 coverage is 100% with descriptions for each parameter, so the baseline is 3. The description adds value by mapping parameters to specific views (e.g., 'view=report uses hours', 'view=stats uses report and window', 'view=volume uses window'), which the schema does not do. This clarifies which parameters are relevant in each mode, going beyond the schema's individual descriptions.

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 states a clear purpose: 'Your account's usage in one of three views' and further explains each view in detail. It explicitly distinguishes this tool from siblings by naming alternatives (get_statement, get_billing_status, list_api_keys) and what they are for, leaving no ambiguity about the tool's specific function.

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 provides explicit when-to-use guidance: 'Use it to answer how much did we use, where, and how fast' and clearly states exclusions: 'Not for invoices (use get_statement), balances (use get_billing_status) or one key's settings (use list_api_keys)'. It also breaks down usage by view, telling the agent which parameters apply to which mode, which is excellent routing guidance.

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