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

With no annotations, the description carries the full burden and does disclose meaningful behavior: read-only introspection of quota state plus the cost trait (free, quota-exempt) and the reset rule (first of next month, UTC). It does not state auth/permission requirements, but for a key-scoped read endpoint that is a small residual gap.

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 tight sentences; the returned fields are front-loaded and the cost/reset caveat follows. Every clause carries information the agent would otherwise have to guess.

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?

No output schema exists, so the description correctly compensates by enumerating the return values and the reset semantics. For a zero-parameter read tool, nothing needed for correct invocation is missing.

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 there is nothing for the description to disambiguate beyond confirming the scope is implicitly the calling key. Baseline 4 applies for a parameterless tool.

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 exact resource (this API key's quota) and enumerates the returned facts: plan, monthly limit, calls used, calls remaining, and reset timing. It is unambiguous and clearly distinct from the listing/comps siblings, though the verb itself is only implied by the tool name rather than stated.

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?

It gives clear call-time guidance by stating the call is free and does not count against the quota, which tells the agent it can invoke this liberally for diagnostics. There is no explicit when-not or alternative-tool comparison, but no sibling covers this capability, so the omission is minor.

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