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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description usefully adds the result cap (limit clamps at 50), but it never defines the recency window implied by 'newly available', which is the key behavioral fact for this tool.

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, zero waste. The core purpose and constraint come first, and the sibling routing follows; every clause earns its place.

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 simple read-only listing tool with a full-coverage schema, annotations, and an output schema covering return values, the description is essentially complete. The only gap is the undefined recency window for 'newly available', which an agent would need to reason around.

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 schema already documents all four parameters including the type enum values and limit default/cap. The description only restates the type values and the limit default/cap, adding no syntax or meaning beyond the schema.

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 (Fetch) and resource (newly available JustWatch movie/show cards), and the scope of results. It explicitly names the sibling tools it is not (justwatch_popular, justwatch_discover, justwatch_search), so an agent can route without opening any 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 three alternative tools with the conditions that select them (broader catalog views, or a specific query). The conditions are stated but a bit loose ('broader catalog views'), and there is no explicit when-not for this tool, so it falls just short of a full 5.

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