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

The annotations already indicate a safe, read-only, idempotent operation. The description adds important behavioral context beyond that: cost is always in USD and billed (never amortized), rows include native_cost/native_currency, and native_cost must never be summed or quoted without naming its currency. This is exactly the kind of non-obvious behavior an agent needs.

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 dense but every sentence earns its place: purpose, sibling distinction, USD rule, native fields, and the billed-cost caveat. Key information is front-loaded, and there is no filler or repetition.

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 read-only two-parameter endpoint with no output schema, the description covers return-value semantics, currency rules, and how it differs from query_costs. The only meaningful gap is the lack of explicit date-parameter guidance, which prevents a perfect score.

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?

The schema descriptions are empty, so the description must explain startDate/endDate. It only says 'over a date range' and never names the parameters, their format, timezone handling, or whether they are effectively required. The agent is left guessing about how to supply these arguments.

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 opens with a specific verb and resource: 'Fetch raw per-service cost entries... over a date range (unaggregated).' It explicitly distinguishes itself from query_costs by calling out that it returns unaggregated individual rows, so an agent can tell them apart.

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 gives an explicit routing directive: 'Prefer query_costs for time-bucketed/aggregated spend — this is for inspecting individual rows.' It further clarifies the lack of a cost_metric parameter compared to query_costs, making the when-to-use decision unambiguous.

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