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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the description only needs to add context beyond them. It does: data source and freshness (Puley Price Index, updated daily), the quota-relevant note 'no read allowance', and the default shaping of results when filters are omitted. Return format is described only in outline.

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?

Front-loaded with purpose, then data source, then parameter behavior in one dense paragraph with no filler. The long app enumeration is long but earns its place by acting as an implicit value list for the required parameter.

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?

With no output schema, the description steps in to sketch the response (local prices, USD amounts, cheapest and priciest countries, US price), which is what an agent needs to plan a call. Gaps are minor: behavior for unknown apps/plans and result shape when countries is supplied are not spelled out.

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?

Schema description coverage is 0%, so the description must carry all three parameters, and it largely does: countries as optional two-letter codes with the cheapest/priciest fallback, plan as optional name-plus-period with the main monthly plan as default, and the app list effectively constrains the required app value. It does not state what happens for an app outside the listed set.

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 a specific resource (subscription prices per App Store country) and enumerates the covered services (ChatGPT, Claude, HBO Max, Notion, etc.), which separates it cleanly from price siblings like drug_prices, gas_prices, ticket_prices and resale_prices. It never explicitly routes against those siblings, so it stops short of a 5.

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?

Usage is only implied: it says the dataset is Puley's own and requires no read allowance, and it explains what happens when optional filters are omitted. There is no explicit 'use this when X, use compare_countries otherwise' guidance, so the agent must infer fit from the resource name.

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