update_library_parts_by_part_id

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

Annotations already indicate this is a non-read-only, non-destructive, idempotent operation, so the description does not need to restate that. It adds useful behavioral detail about selecting audio/subtitle streams and the special value 0 for 'no subtitle.' However, it does not disclose what happens when optional stream parameters are omitted or whether the change persists globally, though annotations soften this gap.

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?

The description is compact and well structured: a one-line summary, the HTTP endpoint, and a clean args list. There is no filler, and each sentence adds value.

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?

Given that an output schema is present, the description does not need to explain return values. The endpoint, required part_id, and all parameter semantics are covered. The main missing piece is behavior when optional parameters are omitted, but overall this is sufficient for a simple parametric update.

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 0%, so the description carries the full burden of explaining parameters. It explains all four parameters clearly, including the important 'Specify 0 to select no subtitle' detail and the all_parts behavior. This fully compensates for the lacking schema 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?

The description opens with 'Set stream selection,' which names a specific action and resource: selecting streams on a library part. The endpoint and args further clarify that it operates on a specific part by ID. It does not explicitly contrast with sibling tools like update_library_streams_by_stream_id_ext or create_player_playback_set_streams, but the 'library parts' resource is distinct enough.

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 guidance about when to use this tool versus alternatives, nor any exclusions or prerequisites. The description implies it is for selecting audio/subtitle streams on a library part, but an agent is not told how it differs from other stream-related update tools or when not to use it.

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