Read spend and usage

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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), so the description is not obligated to restate that. It adds genuinely useful disclosure beyond the annotations: the usage:read scope requirement and the caveat that unpriced requests make any total a floor. It stops short of noting rate limits or freshness/caching behavior.

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?

Two sentences with no filler; the core capability is front-loaded and the auth requirement and pricing caveat follow in priority order. The first sentence is long and clause-dense, but every clause carries information an agent would otherwise have to infer.

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?

An output schema exists, so return values need not be explained, and the bounded range enum removes pagination concerns. The description covers scope, auth, and the pricing-floor caveat, but omits any hint of the consuming context (e.g. budget monitoring vs. cost attribution) that would complete the picture.

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 enum-constrained with documented defaults, so the schema already carries the parameter meaning. The description's 'over a range' and 'broken down by day, model, key or agent' mirror the enums without adding format or default detail beyond them, which is the baseline-3 case.

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 ('what this organization has spent through the gateway over a range') and enumerates the exact breakdown dimensions (day, model, key, agent) plus the metrics returned. No sibling (route_preview, models, chat) does spend reporting, so an agent can route to this tool without ambiguity.

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 context is implied by the spend-reporting framing, and a concrete prerequisite is given ('Requires an API key with the usage:read scope'). However, there is no explicit when-to-use/when-not guidance and no alternatives are named, so routing between this and other tools is left to inference.

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