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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds that the values are country-specific and intended for interpretation, but doesn't disclose anything further about freshness, caching, or breadth of the label set. Adequate but not rich 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?

Two sentences, front-loaded with the tool's function followed by the use case. Every sentence earns its place with zero redundancy.

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 single-parameter reference lookup with an output schema, the description covers purpose and usage context fully. Nothing an agent needs to invoke it correctly is missing, and return values are covered by the output schema.

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 100% and the country parameter is fully documented with its ISO format and US default, so the schema carries parameter semantics. The description says values are country-specific but adds no format or fallback detail beyond the schema, making the baseline of 3 correct.

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?

States a specific verb and resource ('List the age-certification labels JustWatch uses for a country'), and goes further by naming how the output relates to JustWatch title and search tools. An agent can immediately distinguish this reference-lookup tool from content-returning siblings like justwatch_title or justwatch_search.

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?

Gives clear context for when to reach for it: to interpret content ratings returned by JustWatch title and search tools. It names the relevant sibling categories, though it stops short of stating when NOT to use it or listing alternatives by exact name.

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