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

Annotations already declare readOnly/idempotent/destructive=false, so the safety profile is covered. The description adds genuinely non-annotated context: cost behavior ('single HTML read regardless of chapter count') and a full return shape. It does not mention rate limits or the single-book scope constraint beyond 'one book', so not 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?

Front-loads the core definition, then clearly labels When to use / Do not use / Returns. No filler sentences; every clause adds routing or cost information.

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?

No output schema exists, but the description supplies the return structure in full, and annotations cover the safety profile. The only shortfall is the unexplained required lang/slug parameters, which are likely self-evident but not guaranteed.

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 coverage is 50%: page/per_page are documented in the schema, but lang and slug carry no schema description. The description names lang/slug only as return fields, not as callable parameters, so it does not compensate for the coverage gap on those two required inputs.

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 ('Table of contents for one book: ordered chapters with their real titles') and immediately distinguishes itself from the prose-reading sibling. An agent can tell it apart from cyberlibrary_get_chapter and book_meta 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: 'right after cyberlibrary_book_meta, to pick which chapter to read', plus a rationale (cheapest way to survey a long book). Explicit when-not: 'to read prose (call cyberlibrary_get_chapter)'. Both the trigger and the alternative are named.

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