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

Annotations already cover read-only/idempotent/non-destructive, yet the description adds real behavioral detail: the dedup rule ('every metric ... once each, with the plans that limit it'), the semantic meaning of kind counter vs gauge, limit=0 meaning pure metered billing, policy hard vs metered, and the PLAN_NOT_FOUND failure mode. This is substantial context beyond the structured fields.

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?

Purpose and the two modes are front-loaded, and every clause is informative. The dense parenthetical explaining kind and the return-field enumeration make it longer than strictly necessary, but the content largely earns its space.

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, so the description properly carries the return-value burden, enumerating each quota field (metric, kind, limit, policy, pricing, source, reportWith) and its meaning, plus the error case. An agent has everything needed to call and interpret it.

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 coverage is 100%, so the baseline is 3, but the description meaningfully enriches planKey by explaining the shape of results in each presence/absence case and giving an example value ('pro'). The app parameter is not elaborated in the description, but the schema already documents it.

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?

States a specific verb and resource ('List usage-quota metrics with their kind') and immediately contrasts the two modes: with planKey returns that plan's quotas, without planKey returns every metric deduplicated across plans. It explicitly names the sibling it is not ('set_plan_quota changes one'), so an agent can separate read from write without opening a schema.

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?

Gives clear usage context ('Use this when wiring quota checks or usage reporting') and routes to the mutation alternative (set_plan_quota). It does not state explicit when-not conditions beyond naming the read/write split, so it falls just short of the 5-level 'explicit when/when-not/alternatives' bar.

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