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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so safety is covered. The description adds real value beyond that: availability is current ('right now'), search accepts aliases like 'USA'/'UK' as well as codes, and destinations carry a multi_country_only flag — behavioral details the annotations cannot express.

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, all front-loaded — purpose first, then the practical handoff to search_esim_plans, then the caveat. No filler or restated schema.

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 usefully explains what comes back (countries/regions plus country_code, and the multi_country_only marker). A hint about pagination or result size would make it fully complete, but for a 2-param read-only lookup this is close to sufficient.

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%, so both parameters are already documented; baseline is 3. The description reinforces that the search parameter tolerates names, aliases and codes, but adds no format constraints or examples beyond the schema's own text.

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 countries and regions where SimAbroad sells eSIM plans right now') and immediately ties itself to the sibling search_esim_plans via the returned country_code. An agent can distinguish it from get_buy_link and search_esim_plans 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?

Clear usage context: this is the lookup step whose country_code feeds search_esim_plans, and it warns that multi_country_only destinations can't be booked with country plans. It does not explicitly state when NOT to call it or name an alternative list tool, so it stops short of full routing guidance.

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