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

Annotations already declare readOnlyHint, idempotentHint, and non-destructive behavior. The description adds valuable scope limitations: it does not detect the registered network, verify plan eligibility, establish eSIM coverage, or guarantee charges. This helps the agent understand what the tool will and won't return, going beyond the annotations.

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?

The description is two sentences with no wasted words, and the main action is front-loaded. The second sentence provides useful exclusions. It is appropriately sized for a simple two-parameter tool, though the first sentence could more directly state the tool's outcome.

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 an output schema present and annotations covering safety, the description need not explain return values. It sufficiently covers scope and limitations for a country-comparison tool. The only minor gap is that it does not explicitly state that the tool determines roaming status, relying on the title and name for that context.

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%, so the baseline is 3. The description adds meaningful semantics by noting that countries are compared using 'country names and ISO codes', whereas the schema only gives a name example. This clarifies that ISO codes are also accepted, improving parameter understanding.

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 it 'compares entered countries' and provides 'conditional official roaming guidance', which implies the tool checks roaming status. However, the core verb+resource ('check roaming status') is not stated directly, and the mechanism ('compares') is foregrounded over the outcome. It distinguishes from siblings only indirectly through a list of what it does not do.

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?

There is no explicit guidance on when to use this tool versus alternatives like calculate_roaming_cost or check_coverage. The negative list ('Does not detect...') clarifies boundaries but does not direct the agent toward the correct sibling for related tasks. Usage context is left to inference.

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