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

Annotations already declare readOnlyHint and openWorldHint, so the description's added value is the 404 failure mode across the shared id space and the credential-free public nature of the data. It also discloses pagination defaults and the per_page clamp. It stops short of describing the response envelope, which is largely covered elsewhere.

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?

Four dense sentences, front-loaded with the return contract and scoping, followed by the id-space warning and the sibling routing. No filler.

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 an output schema present, return values need not be explained, and the description still names the cast fields. The 404 caveat, credential note, pagination behavior, and sibling routing make this complete for correct invocation.

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 the schema already documents id, page, and per_page. The description restates the same defaults (page 1-based default 1, per_page default 10 clamped to 50) without adding syntax or format detail 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 — a manga's cast — and enumerates the returned fields (character name, native name, billed role, image, favourites). It explicitly names the sibling it is not (anime_title_characters) and the Rubicon between the anime/manga id spaces.

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 negative condition (an anime id here returns 404, use GET /anime/title/{id}/characters instead) and a positive routing hint (use manga_title_staff for staff credits). Nothing is left for the agent to infer.

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