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

Annotations already establish read-only, idempotent, non-destructive, closed-world behavior, and the description still adds substantive traits: aggregate counts only ('never who'), an SFW-only content filter, and a week-to-month window fallback. It also states what is returned (titles plus add-counts), so the agent knows the shape of the result despite no output 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?

A single sentence, front-loaded with the ranking criterion, then the fallback window, privacy guarantee, and content filter. No redundant restatement of the title or of schema-declared defaults.

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?

For a one-parameter, no-output-schema read tool, everything needed to call it correctly is present: what is ranked, over what window, what is returned, and the privacy/SFW constraints. Annotations cover the safety profile, so no additional behavioral burden remains.

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?

There is one optional parameter at 100% schema description coverage, so the schema already explains limit's range and default. The description adds nothing about limit itself; the 'with how many people added each' clause describes output, not the parameter. 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 (List) and resource (anime) plus the exact ranking criterion: most-added by members over the last week/month. That criterion cleanly separates it from search_anime (query-based), whats_airing (airing schedule), get_watch_order, and get_filler_guide without needing to open 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?

The popularity/trending context is unambiguous and the fallback to a monthly window 'when a week is quiet' tells the agent how the tool behaves in low-data periods. It stops short of explicitly routing the agent away from siblings (e.g., 'for title lookup use search_anime'), so no true exclusion guidance is given.

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