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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so safety and closed-world nature are covered structurally. The description adds only the country_id provenance dependency; it says nothing about coverage gaps (country with no operators) or pagination, and an output schema exists so return shape needn't be explained.

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 short sentence, purpose front-loaded, with the dependency and usage trigger packed in without filler. Nothing here is redundant or padded.

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?

For a one-parameter read tool with full schema coverage, an output schema, and annotations carrying the safety profile, the description covers purpose, prerequisite source, and usage trigger. Only edge-case behavior (empty results, whether the list is filtered by country availability) is unaddressed.

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% and the single parameter is already documented as 'id_country from get_countries'. The description merely restates that provenance, adding no syntax, format, or validation detail beyond the schema.

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 and resource ('List mobile operators for a country') and ties the scope to a sibling input ('uses id_country from get_countries'), so an agent can distinguish it from get_countries and the rate/service-type siblings without opening a schema.

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?

Gives an explicit trigger ('use when carrier lookup failed or the user already knows the operator'), which implicitly positions lookup_carrier as the fallback path. It doesn't name that sibling outright or state a when-not-to-use case, so it falls short of a 5.

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