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

With readOnlyHint=true, the safety profile is already covered. The description goes further by specifying what the agent can expect to learn: API plan, usage limits, and remaining quota. Though response format and error cases are not mentioned, the disclosed return values are meaningful for a zero-parameter read-only tool.

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, front-loaded sentence that conveys the entire purpose with no filler. Every word contributes to the tool's meaning.

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, read-only introspection tool, the description is fully complete. It tells the agent exactly what information is returned (plan, limits, remaining quota) and there is no output schema or nested structure to document. Nothing needed to call it correctly 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 has zero parameters, which makes the input schema trivially complete (100% coverage). Per the baseline for zero-parameter tools, the description adds no parameter information, but none is needed.

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 uses a specific verb ('Check') and names a clear resource ('your current API plan, usage limits, and remaining quota'). It is instantly distinguishable from the news-related siblings 'headlines' and 'search-news'.

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?

The description clearly states what the tool does, so an agent can infer when to use it—whenever quota or plan information is needed. No alternative tool serves this same purpose, and the siblings are clearly unrelated, so explicit when-not guidance is unnecessary.

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