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

Annotations already declare this as a safe, idempotent, closed-world read, so the bar is lower. The description adds genuine behavioral context beyond them: the return shape (price tiers per trip length plus inclusions) and the network/carrier scope, which is operationally useful. It stops short of documenting pagination or ordering, but that is largely covered by the output schema.

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?

Front-loaded with what the tool returns, followed by a single routing sentence to the sibling. Every clause earns its place: product types, network, geography, return shape, and alternative.

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-argument, read-only catalog tool with full annotations and an output schema, the description supplies everything the agent needs: what is returned and how it differs from the quote tool. No gaps remain that the structured fields do not already cover.

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 (schema coverage 100%, empty object), so there is nothing to disambiguate; the baseline of 4 applies. The description correctly avoids inventing input semantics for a parameterless catalog call.

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?

Names a specific verb (get) and resource (Spain Internet plans/products), and enumerates the concrete product types returned: eSIM, data SIM card, and 4G+/5G pocket WiFi hotspots. It also scopes geography (mainland, Balearic, Canary Islands) and network (Vodafone Spain), which is far more specific than the generic title.

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 to the sibling: 'quote_spain_internet gives the exact price for given dates,' which distinguishes catalog browsing from price quoting. It does not state exclusions or prerequisites explicitly, but the alternative and its selecting condition are clear.

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