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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds that results are 'live' and that regional coverage varies by plan, but says nothing about result count, pagination behavior, or empty-result handling beyond what limit/offset imply.

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 short sentences, front-loaded with the core action and zero filler. Minor deduction: the example 'popular islands such as Brussels and Bali' is factually sloppy (Brussels is not an island), which slightly muddies the query-format guidance.

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 zero-required-param search tool with no output schema, the description should at least say what comes back and whether results are paginated. It covers input vocabulary and coverage nuance but leaves the returned entity and paging story to inference.

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 0%, so the description must carry parameter meaning. It explains the accepted query forms well (country names, ISO codes, cities, islands) but leaves limit, offset and the 40-value locale enum completely undiscussed.

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 ('search live country and regional coverage') that an agent can distinguish from the plan/pricing siblings. It is clear what is being looked up, though it never says what a result actually is (a destination, a plan, a price).

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?

Usage is only implied: you search coverage before acting on plans/prices. The line 'Regional coverage is specific to each plan' hints that plan-level detail belongs to get_esim_plan or list_esim_plans, but no alternative is named and no when-not condition is given.

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