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

Annotations already declare readOnly and openWorld, so the bar is lower. The description adds genuinely useful behavior beyond the annotations: a hard 20-id batch cap and the fact that unresolved ids are returned alongside the summaries (partial-success semantics), which helps an agent interpret results.

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?

A single sentence, front-loaded with the operation and scope, ending with the partial-success detail. No filler; every clause carries 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?

An output schema exists, so return values need no elaboration, and the description covers the batch cap, input source, and unresolved-id behavior. It is complete enough for correct invocation, with only sibling differentiation left implicit.

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 lang, country, and guide_ids are already documented. The description restates the guide_ids constraint (1-20, sourced from a place's guide_ids) and adds nothing about lang/country, 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?

States a specific verb (lookup) and resource (Apple Guide summaries) with an explicit scope: up to 20 guide ids in one call. The batch nature implicitly distinguishes it from the singular apple_maps_guide, but no sibling is named, so it falls short of a 5.

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?

The 'up to 20 guide ids in one call' phrasing and the 'e.g. a place's guide_ids' hint imply batch-resolution use and a source for the ids, but there is no explicit when-to-use-this vs apple_maps_guide (single) or apple_maps_guides statement, nor any exclusion.

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