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

Annotations already declare this a read-only, idempotent, non-destructive, open-world call, so the safety profile is covered. The description adds genuinely useful context beyond that: the answer comes from esimgomobile's published plan catalog and is live-checked, plus a built-in country network reference, which tells the agent about data provenance and freshness.

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?

Two short sentences, with the usage trigger front-loaded before the data-source explanation. No filler or restatement of the tool name.

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?

An output schema exists, so return values need not be explained. The description covers purpose, trigger, and data provenance for a single-parameter lookup; only minor gaps remain, such as whether the answer reflects plan-specific or network-level coverage.

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?

One required parameter with 100% schema description coverage and an inline example ("Japan"), so the schema already does the work. The description implies the country argument but adds no format, accepted-value, or naming detail beyond what the schema provides.

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 (check) and resource (country coverage) scoped to esimgomobile plans, which distinguishes it from generic siblings like list_country_networks or search_plans. It stops short of naming the adjacent sibling that also answers coverage questions, so differentiation is implied rather than explicit.

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?

"Use when the user asks whether a country is covered" gives an explicit, recognizable trigger condition. There is no when-not guidance, no named alternative for overlapping coverage/plan questions, and no prerequisite stated.

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