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

Annotations already declare readOnly/idempotent/non-destructive/no open world, and the description adds real context beyond them: 'live price' signals real-time (non-cached) quoting, the checkout stays with the traveller, and only one eSIM per booking. It still doesn't cover failure modes or how stale a quote can become.

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?

Three sentences, front-loaded with the return value, then the non-action boundary, then the date semantics. Every sentence carries distinct information and nothing is repeated from the schema or annotations.

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?

Output schema exists and annotations carry the safety profile, yet the description still tells the agent what comes back (price + link) and what it must not assume (no order placed). With both params fully documented, nothing needed for a correct call is missing.

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 genuinely adds meaning: dates are inclusive of both first and last day, with a worked example (2–9 November = 8 days). That disambiguates the most common off-by-one error an agent would otherwise make.

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?

Precise verb+resource: it returns the live Portugal eSIM price for given dates plus a pre-filled booking link. It does not name the sibling get_esim_portugal_plans, so the boundary between 'quote/book' and 'list plans' is left for the agent to infer.

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?

Clear context on when this is the right call (traveller wants a price and a ready-to-pay link) and an explicit boundary—'It does not pay or place an order'—which steers the agent away from treating it as a purchasing tool. No alternative sibling is named, so it stops short of full when/when-not routing.

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