add_to_watchlist

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

No annotations are provided, so the description must carry the full burden of behavioral disclosure. It does mention the mutative prerequisite, but it does not disclose what happens on success, whether the operation is idempotent, or any side effects beyond the flag. For a write operation, this is a significant 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 a single, front-loaded sentence that says everything needed in as few words as possible. No filler or redundant information.

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 the tool's simplicity (one parameter, no output schema), the description covers the core purpose and a critical prerequisite. However, it lacks information about behavior on duplicates, return value, or error conditions. With no annotations, this leaves some ambiguity, making it minimally adequate rather than complete.

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?

The schema fully describes the only parameter 'ratingKey' as 'The rating key of the media item', so schema coverage is 100%. The description adds no additional semantic detail beyond the schema, matching the baseline of 3 for high schema coverage.

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 clearly states a specific verb+resource: 'Add a media item to watchlist'. It distinguishes from sibling tools like 'remove_from_watchlist' and 'get_watchlist' by explicitly indicating the action of adding.

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?

The description provides a clear usage condition: 'requires PLEX_ENABLE_MUTATIVE_OPS=true'. This tells the agent when the tool can be invoked, effectively establishing an exclusion when the flag is false. It does not explicitly name alternatives, but the purpose and sibling names make the differentiation obvious.

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