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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds the useful behavioral fact that output is derived recommendations keyed to a relationship type, but it says nothing about pagination, rate limits, or coverage gaps, so it adds only modest context beyond the annotations.

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?

Two sentences, no filler, and the core capability is front-loaded before the sibling routing. Every clause earns its place.

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?

An output schema exists, so return values need not be described, and the required ASIN plus relationship types are covered. Only minor gaps (no sense of result set size or ordering) keep it from a 5.

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 100%, but the schema's similarity_type only says 'How to relate titles to the given ASIN' with no enum. The description supplies the actual candidate relation values (series, narrator, author, similarity), which is meaningful information the schema lacks. asin and limit remain purely schema-documented.

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?

The description gives a specific verb ('Fetch') and a precise resource ('Audible title recommendations related to a known audiobook ASIN'), and it enumerates the four relationship axes (series, narrator, author, similarity). This makes it immediately distinguishable from the sibling detail/search/review tools.

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?

It states the precondition (a known ASIN is required) and explicitly routes to three named alternatives with their conditions: audible_product for title details, audible_product_reviews for reviews, audible_search to discover titles. The when-to-use boundary is fully spelled out.

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