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

Annotations already declare readOnlyHint, idempotentHint, non-destructive, and openWorldHint=false, so the safety profile is covered. The description adds genuine context that the destination argument accepts a country, region, or global plan, but says nothing about the shape of the answer or how ambiguous country input is resolved.

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 tight sentences with zero filler; the core purpose leads and the accepted input forms follow immediately. Nothing is redundant against the title or 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?

For a simple read-only coverage check with no output schema, the description gives enough to call the tool correctly, including valid input forms for both required parameters. The main remaining gap is that it never characterizes the response (boolean vs. coverage detail), which matters slightly when no output schema exists.

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 only 33% (locale is documented; country and destination are bare), so the description carries real weight here: it explains that country may be a name or ISO code and that destination spans country, region, or global plan. This meaningfully compensates for the undocumented required parameters, though it does not spell out locale's role.

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?

The description states a specific verb and resource — answering whether a destination covers a country — and frames it as the user-facing question it resolves ("does this eSIM work in <country>"). It is clearly distinct from siblings like get_destination_info or list_destinations, though it never names them, so differentiation is inferred rather than stated.

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?

The framing implies the use case (a yes/no coverage question for a plan, region, or global destination), which is enough to infer when the tool applies. However, it gives no explicit when-not guidance and never points to alternatives such as get_destination_info for richer detail or list_destinations for enumeration.

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