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 nothing beyond that: it does not say how filters combine (AND/OR), how defaults behave, or what kind of result set (offers, availability) is returned. With annotations in place the bar is lower, but zero added context warrants a low score.

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?

It is a single four-word fragment with no wasted clauses in a trivial sense, but it is under-specified rather than concise — the brevity comes from omitting the information an agent needs, not from tight editing. There is no front-loaded statement of purpose worth reading.

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?

This is a 10-parameter filter tool sitting among ~20 JustWatch siblings, and the only output of relevance beyond the output schema is guidance on how the filters interact and when to prefer this over justwatch_search. The output schema removes any need to describe return values, but the invocation-side context is essentially absent, leaving the definition incomplete for a tool of this complexity.

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% across all 10 parameters, so the schema already documents types, defaults, enums and formats (e.g. genre/provider short names, monetization types). The description adds no parameter meaning whatsoever. Per the rubric, a 100% coverage schema yields a baseline of 3 when the description contributes nothing extra.

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 restates the tool name almost tautologically: 'justwatch_discover' becomes 'JustWatch filtered title discovery'. It hints that filtering is involved but names no specific verb, resource set, or scope that would separate it from siblings like justwatch_genre_titles, justwatch_provider_titles, justwatch_popular, or justwatch_search. An agent cannot tell from the text alone which discovery entry point to pick.

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?

There is no when-to-use guidance, no exclusions, and no mention of the many alternative JustWatch tools (search, popular, new, genre_titles, provider_titles). The word 'filtered' weakly implies this is the tool for multi-facet queries, but the agent must infer that entirely. This is effectively no guidance.

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