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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds value beyond that by disclosing geographical coverage (mainland, Madeira, Azores) and the shape of what comes back (tiers plus inclusions). It doesn't discuss caching, freshness or pagination, but those are minor for a static catalog lookup.

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: the first front-loads what the tool offers, the second handles return content and sibling routing. No filler and nothing buried.

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 no-parameter, read-only catalog tool with no output schema, the description supplies the scope, the nature of the return (tiers plus inclusions) and the routing rule. An agent has everything needed to call it correctly.

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 per the rubric the baseline is 4. The description correctly implies the tool is parameter-free by directing date-specific pricing to the sibling quote tool.

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 resource (Portugal Internet eSIM, with explicit coverage of mainland, Madeira and Azores), its key attribute (truly unlimited data, priced by trip length) and its return content (price tiers and inclusions). It is clearly distinguishable from the sibling quote tool without opening either schema.

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?

Explicitly routes the agent: this tool returns the tier structure, while 'quote_esim_portugal gives the exact price for given dates'. The condition that selects each tool is stated rather than left to inference.

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