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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so safety is covered. The description adds genuinely new behavioral context: it exposes per-minute rate-limit consumption, which is not derivable from annotations or the empty schema and matters for pacing calls. It does not state auth requirements or what happens when quota is exhausted.

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?

A single tight sentence with no padding, front-loading the returned information. Slightly clipped grammar ('The plan on this key') leaves the subject implicit, which costs a little clarity but not length.

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 zero-parameter, annotation-rich, read-only tool with no output schema, the description covers the two things an agent needs to know it will get back (plan and remaining calls). Only the exact response shape and quota-exhaustion behavior are unstated, which is a minor gap.

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 zero parameters and the schema is empty, so there is nothing for the description to explain; baseline 4 applies. The description correctly introduces no parameter discussion.

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 name 'whoami' is ambiguous on its own, but the description disambiguates it precisely: it reports the plan tied to the current key and remaining calls this minute. No sibling tool in the list returns account/plan or quota data, so the resource is effectively unique, though the description states no verb and relies on implication ('The plan on this key').

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 via 'how many calls remain this minute' – an agent can infer this is a rate-limit/quota check, but there is no explicit statement of when to call it (e.g. before bulk operations) or when not to. No alternatives are named, though none of the siblings overlap functionally.

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