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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so safety is covered. The description adds value beyond these by spelling out the return shape ({generated_at, total_items, readable_items, languages[]}) and the ordering role of the call, though it says nothing about rate limits or the size/cost of the catalog response.

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?

Front-loads the purpose, then routes with labeled 'When to use' / 'Do not use' clauses and closes with the return shape. Every sentence carries distinct information; no filler or repetition of the title.

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?

There is no output schema, and the description compensates by enumerating the top-level return fields and the per-language entry contents. Combined with annotations covering the safety profile, nothing an agent needs to call this correctly is missing.

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 per the rubric the baseline is 4. There is no parameter syntax for the description to clarify, and it correctly describes the returned fields instead.

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+resource: indexing 'Every language catalog in Cyber Library with item counts and the corpus generation date.' It distinguishes itself from siblings by explicitly naming cyberlibrary_language_shard and cyberlibrary_get_markdown/get_chapter as different tools, so an agent can route without opening a 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?

Explicit 'When to use: first call in any session' with the reason (to pick a language before fetching a shard), plus a 'Do not use' clause naming the correct alternatives for each excluded case. Both when and when-not are covered with named substitutes.

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