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

Annotations already declare readOnlyHint/idempotentHint/destructiveHint, so safety is covered. The description adds real behavioral context beyond that: 'a missing field means unknown, not "no"' disambiguates null semantics, and the note that phone/email live on the linked gym page explains an intentional omission. It does not cover behavior on an unknown/invalid slug.

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?

Three tight sentences, front-loaded with the field list, then the unknown-vs-absent rule, then the phone/email caveat. Every sentence conveys information an agent would otherwise have to guess.

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, the description carries the return-shape burden and does so by enumerating returned fields and clarifying null semantics. Combined with annotations covering safety, an agent has everything needed to call it correctly.

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%, so both slug and lang are already documented in the schema. The description reinforces slug provenance but adds no syntax or format detail beyond the schema, and never mentions the lang parameter or its default. 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+resource ('Public details of one gym by its slug') and enumerates exactly what is returned: address, website, affiliation, offerings, schedule, last-updated timestamp. It also distinguishes itself from the sibling find_gyms by naming it as the source of the slug.

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 description ties usage to find_gyms ('slug (from find_gyms)'), making the lookup-after-search workflow clear, and the 'public details' framing implies the non-authenticated read case. It stops short of explicit when-not-to-use guidance or naming alternatives for other lookup needs.

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