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

With readOnlyHint/openWorldHint already declaring the safety profile, the description adds genuinely new context: what each row contains (price of the cheapest single-country plan, page link) and that it covers only single-country plans, which is not stated in annotations or schema. No output schema exists, so this payload disclosure carries real weight.

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: the first defines the resource and its returned fields, the second routes usage. Front-loaded, no filler, every clause earns its place.

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 two-optional-param read-only list tool with no output schema, the description covers purpose, payload shape and usage triggers. Minor gaps remain: whether the list is complete/unpaginated and whether prices reflect one-time vs per-day plans.

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% and both parameters are enums with documented defaults (locale, currency and their locale-dependent default pairing), so the schema does the heavy lifting. The description adds nothing about locale or currency behavior, making 3 the appropriate baseline.

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 where VIDI sells travel eSIM data plans') and adds the returned payload (cheapest single-country plan price + country page link), which cleanly separates it from search_esim_plans and search_destinations.

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?

Gives concrete triggering questions ('does VIDI cover X', 'cheapest eSIM for X'), which is strong positive guidance. It stops short of naming an alternative tool or exclusion (e.g., when to prefer search_esim_plans for multi-country plans), so it is not a full when/when-not spec.

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