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 real value beyond them by disclosing that prices are live-checked against an external site, which signals freshness guarantees and possible latency/cost of the call.

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 sentences, zero filler, and the usage trigger is front-loaded before the content description. Every clause carries information (trigger, content, currency, freshness).

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 parameters, a rich annotation set, and an output schema already describing the return shape, the description only needs to supply the trigger and scope — both are present. An agent has everything required to decide to call it and to interpret the result.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate; the baseline for a no-arg tool applies. The schema is empty and fully covered, and no parameter guidance is missing.

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 the published plan catalog) plus the notable scope detail that prices are USD and live-checked against esimgomobile.com. It is clearly distinct from recommend_plan/compare_plans/get_plan_details in spirit, but it never names a sibling, so the 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 what esimgomobile plans exist or what an eSIM costs" gives an explicit trigger condition, which is exactly what an agent needs for routing. It stops short of stating when NOT to use it or pointing to search_plans/recommend_plan for filtered or personalized queries.

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