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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety and open-world scope are covered. The description adds the content categories returned (credits, clips, backdrops), but says nothing about pagination, rate limits, or auth requirements, which is a modest addition over 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 tight sentences with the core purpose front-loaded and routing guidance second. No wasted words, though it could be marginally denser.

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 an output schema present and annotations covering the safety profile, the description supplies the remaining essentials: what extras are returned and how to obtain the required id. Nothing critical for correct invocation is missing.

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%, with the id pattern (tm[0-9]+/ts[0-9]+) and country/language defaults fully documented in the schema. The description only echoes the raw id format already stated there, so baseline 3 is appropriate.

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 states a specific verb (Fetch) and concrete resources (credits, clips, backdrop images) scoped to a known JustWatch title id, and explicitly distinguishes itself from justwatch_title ('this tool for its media extras'). An agent can tell it apart from the sibling without opening the schema.

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?

It names the prerequisite path (use justwatch_search to obtain the raw tm…/ts… id) and the sibling to choose for the main record (justwatch_title). It gives clear context for when to use this tool but stops short of explicit exclusions or when-not conditions.

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