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

Annotations cover the safety profile (read-only, idempotent, non-destructive), and the description adds substantial context beyond them: no payment occurs, delivery must be chosen on the page for physical products, dates are inclusive, the price covers one device with quantity editable, and SIM/WiFi have multi-day delivery lead times while eSIM can start today. That last point materially affects whether a call is even valid.

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?

Purpose and return value are front-loaded, and each subsequent sentence carries a distinct constraint (payment scope, date arithmetic, quantity, delivery lead times). Dense but largely waste-free; the checkout-flow sentence could be tightened slightly.

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?

An output schema exists so return values need no elaboration, yet the description still tells the agent what comes back (price plus pre-filled booking link). Combined with the three required params and the date/delivery caveats, an agent has everything needed to call this 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?

Schema coverage is 100%, so the baseline is 3, but the description adds real meaning: the inclusive date semantics ('2 to 9 November is 8 days') remove ambiguity the pattern and format do not resolve, and it explains the per-device quantity assumption. It does not restate the product enum values, which the schema already documents well.

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: it returns 'the live price of one Spain Internet product for the traveller's dates, and a booking link with those dates already chosen', and it clarifies what it does NOT do ('does not pay or place an order'). The sibling get_spain_internet_plans is not named, so the agent must infer that this tool prices a single product while the sibling enumerates options.

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 clear context and an explicit exclusion: this is a quote step that hands off to a checkout the traveller completes, so it is not the ordering tool. It also explains the end-to-end flow after the link. It stops short of naming the sibling as the alternative for browsing plans.

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