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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered structurally. The description adds relevant behavioral context beyond annotations: the required `read` scope and the specific usage metrics returned. It does not contradict the 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: it starts with the core operation, enumerates the returned metrics, then adds the endpoint and required scope. Every sentence contributes useful information without 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?

There is no output schema, but the description explicitly lists the returned metrics, which compensates well. With the single optional parameter fully documented in the schema and annotations covering the read-only/open-world safety profile, an agent has enough information to invoke this tool correctly.

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 has 100% description coverage for the single `period` parameter, including its enum values and default. The description adds no additional parameter semantics, so the baseline score of 3 is appropriate because the schema does the heavy lifting.

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 usage and spend for the calling key. It further specifies exactly which metrics are returned (wallet_usd, consumed_usd, query count, budget remaining) and maps the operation to GET /v1/usage, making the tool's purpose unambiguous relative to the sibling tools.

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 includes a key prerequisite—the calling key's `read` scope—which is useful context for whether the call can succeed. However, it does not explicitly say when to use this tool versus alternatives such as get_status, nor does it state when-not to use it.

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