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

Annotations already declare readOnly/idempotent/non-destructive, so the description's added value is the 30-day rolling window, newest-first ordering, and two real constraints: only lists the viewer is permitted to see, and SFW titles only. It does not mention pagination or result limits, which keeps it from a 5.

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 that front-loads the resource and then layers scope, ordering, and filters. Dense but every clause earns its place; slightly heavy as one long sentence rather than split for scanability.

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 no output schema, the description carries the return shape and does so reasonably: entries grouped by @username, newest first, filtered by visibility and SFW. Pagination/result-count behavior is the one missing piece an agent might need.

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 tool takes zero parameters, so parameter semantics baseline is 4. The description correctly adds no parameter narrative and instead spends its words on scope and result shaping.

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?

Names a specific verb and resource ('List what the people the signed-in person follows ... have been watching or finished') with explicit scope, time window, and ordering. This is clearly distinguishable from siblings like my_library (own list) and popular_anime (global popularity).

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 social-graph scoping ('people the signed-in person follows') implies when this tool applies versus my_library, but there is no explicit when-to-use/when-not guidance or named alternative. The visibility and SFW notes are filtering behavior, not selection guidance.

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