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

Annotations already establish readOnlyHint=true, openWorldHint=false, and destructiveHint=false, so the safety profile is covered. The description adds that results include starting prices and both country and regional/global coverage, which is moderate additional context. It does not explain pagination, price currency, or result ordering.

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?

It is short and front-loaded: purpose and output content come first. But the entire second sentence is spent on a parameter that is not in the schema, so part of this brevity is wasted and misleading rather than efficient.

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, read-only annotations, and a single fully described parameter, most of the burden is handled elsewhere. Still, the description leaves unclear what the tool actually returns per destination and how the nonexistent country_iso relates to the real coverage_type filter.

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% for the single coverage_type parameter, so the baseline is 3. But the description instead documents a 'country_iso' parameter that does not exist in the schema, which actively misleads about how to call the tool rather than supplementing 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?

The verb and resource are specific ('List travel eSIM destinations'), and it distinguishes itself from the get_esim_plans sibling by noting that results carry starting prices. However, the scope is muddied because it describes a country_iso input that this tool does not accept.

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 sentence 'Use it for get_esim_plans' implies this tool is the discovery step before fetching plans, which is useful routing. But the phrasing is vague and never states when not to use it or how coverage_type filtering changes the choice.

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