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

Annotations already declare readOnly, idempotent, and non-destructive. The description adds crucial behavioral context beyond annotations: failed calls still consume quota, and this tool is the authoritative source for valid enum values. This is valuable operational information not present in the structured fields.

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 with no redundant words. The first sentence immediately identifies the resource and its scope, and the second delivers a practical usage warning. Every word earns its place.

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 no notable complexity, the description fully covers what the tool does, when to use it, and why it matters (quota impact). No additional context is needed.

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, so schema coverage is trivially 100%. The description adds semantic value by explaining that the output provides valid values for parameters of other tools (e.g., country codes, category IDs), which is essential for correct parameter usage across the API.

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's purpose: it lists 'the enum values every other tool accepts,' specifically countries, platforms, chart types, and categories. This distinguishes it from all sibling tools, which are data retrieval operations, not reference data.

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 when to use: 'Call this before guessing a country code or category id.' It also provides a strong rationale—invalid parameters fail and count against the daily quota—making the usage context very clear.

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