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

Annotations already declare the write, non-idempotent, non-destructive profile, so the bar is lower; the description still adds that records surface in history and stats, which is real effect information. It does not address duplicate logging or what happens if the same repeat is logged twice, which is the notable gap for a non-idempotent write.

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 short sentences with zero waste: what it does, when to use it with examples, and how it relates to the status mechanism. The key distinction is front-loaded.

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 full schema coverage, no output schema, and annotations covering the safety profile, the description supplies everything needed to decide and invoke. Minor omission: it does not say whether the title must already exist in the library or what happens on an unknown title, though the schema hints at candidate resolution.

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%, so media_type, event_type, event_date, title, item_id, rating and notes are all already documented, including defaults and enums. The description only reinforces that a date accompanies the log; it adds no syntax or disambiguation beyond the schema, so baseline 3 applies.

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?

States a specific verb and resource ('Log a completion or a re-watch/re-read/re-listen with a date') and explicitly separates itself from status-based tracking: 'The first finish is tracked by status; this records repeats.' An agent can distinguish this from update_status or set_progress without opening any schema.

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?

Gives an explicit trigger ('Use when the user mentions finishing something again') plus two concrete utterance examples, and an explicit exclusion rule (first finishes go through status). The when/when-not/alternative structure is fully present.

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