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

Annotations already declare readOnlyHint=true and idempotentHint=true, covering safety. The description adds value beyond that by specifying the authentication requirement ('Needs an API key') and detailing the output content (plan, watermark, quota used/remaining/reset date), which is essential since there is no output schema. This goes beyond the annotations.

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?

Three crisp sentences with no filler. The first line front-loads the output information, the second covers authentication, and the third gives usage guidance. Every sentence earns its place, making it efficient for an agent to parse.

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 tool with no output schema, the description fully covers what the agent needs: the data returned (plan, watermark, quota used/remaining/reset date), the requirement for an API key, and when to invoke it. There are no missing details that would hinder correct usage.

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 input schema has zero parameters, so there is nothing for the description to explain. The description still adds the helpful context that an API key is required, which is not a parameter but a prerequisite. With no parameters, the baseline is 4, and the description meets that without needing to compensate for schema gaps.

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 states exactly what the tool returns: the API key's plan, watermark status, and monthly quota details (used, remaining, reset date). This is a specific resource (usage/quota) and is clearly distinct from sibling tools that deal with card rendering or meta tags, so an agent can easily identify its purpose.

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 gives explicit usage scenarios: 'Check it before batch renders, or when a render came back watermarked unexpectedly.' This tells the agent exactly when to call it, and because the tool is unique among siblings, no exclusion is needed. This is direct, actionable guidance.

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