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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description's added value is enumerating the returned fields, which substitutes for the missing output schema, but it says nothing about ordering, result size, or pagination.

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?

One compact sentence with no filler, and the resource identification is front-loaded. It spends its words on field enumeration rather than on guidance, but nothing is redundant.

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, listing the returned fields is genuinely useful and partially compensates. However, for a list tool it omits practical invocation details such as whether results are all libraries by default and how the city filter narrows them.

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% and the single optional city parameter is documented in the schema with examples (Yerevan, Gyumri). The description adds no filtering semantics beyond that, so the 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?

The description identifies the resource precisely (directory of libraries in Armenia) and enumerates the fields returned, which lets an agent separate it from the book/author siblings. The verb is only implied by 'directory ... that ELIB lists' rather than stated as 'List libraries', but the meaning is unambiguous.

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?

There is no statement of when to use this tool, when not to, or how it relates to the book/author siblings. The city filter parameter exists but the description never mentions it, so an agent gets no routing or scoping advice.

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