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 country and language scope the catalog, which is useful behavioral context, but says nothing about pagination, result ordering, or how 'similar' is determined. With annotations and an output schema present, a 3 is appropriate.

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 core action, and the prerequisite and alternatives are packed efficiently. The middle clause ('its raw tm… or ts… id') is slightly telegraphic, but nothing is wasted.

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 read-only lookup with a full output schema and fully documented parameters, the description covers purpose, id acquisition, catalog scoping, and sibling alternatives. An agent has everything needed to invoke it correctly.

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 coverage is 100%, so the baseline is 3, but the description adds meaning beyond the schema by explaining that the required id is obtained via justwatch_search and that country/language scope the catalog. That is genuine guidance not present in the field descriptions.

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: 'Find movies or shows similar to a JustWatch title.' An agent immediately knows this is a recommendation/related-title lookup, and the surrounding sentences distinguish it from justwatch_title (seed details) and justwatch_title_offers (availability across markets).

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 names the prerequisite path (use justwatch_search to obtain the raw tm…/ts… id) and routes to alternatives for adjacent needs (justwatch_title for details, justwatch_title_offers for cross-market availability). When-to-use and sibling selection are both spelled out.

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