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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description adds real behavior beyond them: detail=true silently caps limit at 25 and swaps the payload from progress fields to full item records. That cap-and-switch interaction is exactly the kind of hidden trait that prevents bad calls. It stops short of describing ordering or default page size.

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?

Three tight sentences, front-loaded with what the agent gets, then the filters, then the mode switch. The parenthetical field list ('watched, viewCount, actors, collections…') is informative rather than filler, and nothing repeats the schema.

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 no output schema, the description usefully sketches both return shapes and the truncation rule, which is what an agent needs to pick a mode. It doesn't state result ordering or that the default limit is 20, so it isn't fully airtight, but nothing critical 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 only 25%, so the description carries the burden — and it does: library is explained as a section filter, user as a Plex Home user selector, and detail's dual effect (cap + payload shape) is spelled out. Only `limit` is left to the schema, which supplies min/max/default, so the gap is minor.

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?

Names a very specific resource — the next unwatched episode per in-progress show plus partially-watched movies — with the delivered value (progress position) stated up front. The 'in progress' scope naturally separates it from siblings like watch_history and now_playing without needing to name them.

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?

Usage is implied through the optional narrowing flags ('optional library narrows to one section', 'user shows a Plex Home user's list'), but it never states when to prefer this over watch_history, now_playing, or search, nor any exclusions. An agent can infer the use case from the purpose but gets no routing guidance.

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