update_metadata

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

Annotations already state readOnlyHint=false and destructiveHint=false, so the mutating nature is known. The description adds the environment variable requirement, which is useful extra context. However, it doesn't disclose any other behavior, such as the fact that several fields 'replace' existing values (though that is in the schema).

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?

One concise sentence that states the core purpose and the key requirement. Every word is useful, and the structure is front-loaded with the action. There is no wasted text.

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?

The tool has many parameters but the schema covers them exhaustively. The description provides the critical mutative-ops prerequisite and the annotations cover safety profile. It could mention that all fields are optional (except ratingKey) or that some fields replace existing data, but these are already in the schema, so the context is fairly 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 input schema has 100% description coverage for all 14 parameters, so the schema fully documents each field. The description adds no parameter-specific information, so it relies entirely on the schema. This meets the baseline for high 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?

It clearly states the action ('Update metadata fields') and the target ('a media item'), which distinguishes it from the many read-only sibling tools. However, it doesn't explicitly differentiate from the similarly named 'update_metadata_from_json' tool, so it's not a perfect 5.

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 includes a key prerequisite: 'requires PLEX_ENABLE_MUTATIVE_OPS=true'. This gives clear context about when the tool is usable (only if the env var is set). It doesn't explicitly say when not to use it or mention alternatives, but the prerequisite provides strong guidance.

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