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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely useful behavioral context beyond that: the data is 'credential-free public Numbeo data', and the response shape varies by family (headline indices plus optional sub-index sections and/or itemized prices). That variability warning is valuable and not conveyed by 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?

Three tight sentences that front-load the resource and scope, then the data-source caveat, then the sibling pointer. No filler. Slightly dense in the first sentence, but nothing is wasted.

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 an output schema present, return values need not be enumerated, and annotations cover the safety profile. The description still covers purpose, source, credential-free access, response variability, and the country-level alternative, leaving little an agent would need before calling it. Only the unmentioned ranking siblings 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 description coverage is 100%, with both slug ('Numbeo city slug, e.g. Los-Angeles') and index (exact enum values) documented in the schema. The description restates the slug and paraphrases the family list without adding format, validation, or casing rules, so baseline 3 is correct.

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 ('Returns one city's data for a Numbeo index family') and enumerates the six possible families, plus the shape of what comes back (headline indices, sub-index sections, itemized prices). It explicitly contrasts itself with numbeo_indices_country, so an agent can distinguish it from siblings without opening schemas.

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?

Names a concrete alternative ('Use numbeo_indices_country to get a Numbeo country's data') with the condition that selects it, which is strong when-to-use guidance. However, it doesn't address the other nearby siblings (numbeo_indices_rankings, numbeo_indices_rankings_by_country), so the routing is only partially complete.

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