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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the safety profile is known. The description adds the crucial behavior that sign-in is required)Skip, specifying two authentication methods and a link to create credentials. This adds meaningful context beyond annotations, though it doesn't describe the output format beyond 'informational page'.

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?

The description is two sentences, front-loading the primary purpose and then providing essential authentication guidance. Every sentence adds value, with no filler. The critical sign-in requirement is placed prominently after the purpose.

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 tool with an output schema and readOnly annotations, the description is quite complete. It covers purpose, usage timing, and authentication details. The only minor gap is that it doesn't explicitly state that no parameters are required (though the schema shows this), which is trivial. The output schema presumably details the response structure.

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 parametersaday, so the description need not explain parameter semantics. It correctly focuses on what the tool returns, which is abundant. With 100% schema coverage (empty schema), the description compensates fully for the lack of parameters.

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 clearly states the tool checks the signed-in account's remaining credits and current plan name, and retrieves the informational page about plans and entitlement. It uses specific verbs ('Check', 'get') and a clear resource ('signed-in account', 'informational page'), which distinguishes it from siblings like 'list_models' or 'generate_image'.

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?

Explicitly instructs to use this tool before generating, and details the sign-in requirements (OAuth or API key) and where to create the key. It provides necessary context for when to call it, though it doesn't explicitly mention alternatives; however, the use case is so unique that no alternative is implied.

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