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

Annotations already declare readOnlyHint=true and openWorldHint=false. Beyond them, the description adds the notable reassurance 'Does not spend credits' — valuable because credit tooling often has side effects — and clarifies scope is limited to the caller's active organization. It does not cover pagination or result limits, which are minor given the read-only 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?

Three short sentences, each earning its place: the purpose and returned breakdown come first, the optional window second, and the no-side-effect reassurance last. No filler or redundancy.

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?

With no output schema, the description compensates by describing the return shape (totals, spend by tool, spend by day) and the org scoping. Annotations carry the safety profile, so an agent has enough to call it correctly, though the sibling routing and parameter window semantics remain underexplained.

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 are optional, so the schema already documents startDate/endDate inclusive ISO-8601 semantics. The description only restates that they form an optional window, adding no format or default-behavior detail beyond the schema — the baseline 3 for fully covered schemas.

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 specific verb and resource ('Get aggregated credit usage') and enumerates the aggregation dimensions returned (totals, by tool, by day). It implicitly separates itself from get_credit_balance and get_credit_history by calling out aggregation, but it never names those siblings to make the distinction explicit.

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 only implied: the agent can infer this is the reporting/summary tool while balance and history cover other needs, but the description never says when to pick this over get_credit_balance or get_credit_history. 'Does not spend credits' hints at a when-not condition without stating one.

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