cost_report

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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description still adds useful behavior beyond them by disclosing that the values are estimates and that results cover three distinct time windows plus budget remaining. It stops short of saying how fresh the estimate is or where budget data originates.

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?

One sentence, zero filler, with the most important information (what is returned) front-loaded. Nothing could be removed without losing meaning.

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 zero parameters, read-only annotations, and an output schema that documents the return shape, the description covers nearly everything an agent needs to select and call it. The only remaining gap is data freshness/estimation basis, which is minor given the 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?

The tool takes no parameters and the schema is an empty object, so there is nothing for the description to disambiguate. Baseline 4 applies since no semantic gap exists.

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 pairs a specific verb ("Show") with a specific resource ("estimated spend" / "remaining budgets") and enumerates the aggregation windows (today, this month, total). It leaves no ambiguity about what the tool returns; only an explicit nod to the sibling image/video tools is absent, and those are unrelated enough that no differentiation is needed.

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: an agent can infer this is the tool to call for spend/budget questions, but there is no explicit when-to-use framing, no statement of prerequisites (e.g. authentication or billing scope), and no named alternatives. For a zero-parameter reporting tool that is largely self-evident, this is adequate but not instructive.

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