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

readOnlyHint=true already tells the agent this is a safe read, and an output schema exists so return shapes need not be spelled out. The description does add one genuinely useful behavioral detail: daily-limit data is only present on paid plans, so the agent knows fields may be absent. Beyond that it says nothing about auth, caching, or failure behavior, so the bar set by the annotations is only modestly exceeded.

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 short sentences: the first states what is returned, the second when to call. Content is front-loaded and every clause earns its place, with the paid-plan caveat correctly attached inline to the affected data.

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 an output schema covering return values, zero parameters, and a readOnly annotation, the description covers everything needed to decide to call it and to interpret the result. Only minor gaps remain, such as what happens if the call itself is unauthorized or rate-limited.

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, so parameter semantics are trivially satisfied and there is nothing for the description to compensate for. No misuse of the schema is possible here.

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 names the concrete resource it returns: plan/tariff, project slot occupancy, and daily quota remainders. This clearly separates it from the list_*/read_* siblings, which all deal with project content rather than account state. It does not explicitly name a sibling it replaces or excludes, and the name 'whoami' alone would suggest identity rather than quota, so the description is doing necessary corrective work.

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 two explicit trigger conditions: at session start, and after another tool fails due to a limit. That is concrete, actionable when-to-use guidance an agent can act on without inference. It stops short of 5 because it names no alternative tool or when-not condition.

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