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 restates enum values and defaults that the schema already documents, adding only light behavioral context (which filters can be combined for chart-style queries). It says nothing about result ordering, pagination, or rate limits.

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 the core purpose, followed by constraints and the sibling routing. The middle section reads as an enum/default dump that partially duplicates the schema, but overall it is a tight, information-dense block with no filler sentences.

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?

An output schema exists, so return values need not be explained, and annotations cover the read-only/open-world profile. For a 10-parameter, all-optional discovery tool the description covers the primary filter surface, though it never mentions the limit/cap behavior and leaves the differentiation from justwatch_popular and justwatch_new unstated.

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%, so the schema already carries the parameter documentation and the baseline is 3. The description duplicates the type and monetization_types enums and the country/language defaults, and its one genuinely additive element is the providers+production_countries combination example, which is not enough to lift it above baseline.

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 clear verb+resource ("Returns popular movies and shows") plus the filter axes it accepts, and explicitly names the sibling it is not (justwatch_search). It does not, however, distinguish itself from other discovery-style siblings like justwatch_popular, justwatch_new, or justwatch_genre_titles, which overlap with the stated 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?

Names the alternative ("Use justwatch_search to search JustWatch titles") and gives a concrete usage pattern: combine providers with production_countries to chart Korean/Japanese titles on a service. No explicit when-not conditions are given for the other discovery siblings.

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