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

Annotations already declare readOnly, idempotent, non-destructive and open-world, so the bar is lower, yet the description adds real value by enumerating what does NOT happen: no price reservation, no order creation, no card charge, no eSIM issuance. It omits operational traits an agent might need, such as link expiry or whether the same plan_id always yields the same URL, which is why it is not a 5.

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 short sentences, front-loaded with what is returned and followed by the negative scope. Every clause carries distinct information and nothing is repeated from the name.

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?

No output schema exists, but the description compensates by stating the return is a URL only, which is the key fact for an agent building a downstream step. For a one-parameter tool this is nearly complete; the remaining gap is the absence of guidance on obtaining a valid plan_id and on error behavior for unavailable plans.

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 single parameter plan_id has zero schema description coverage and the description never explains it — no hint that it should come from get_plan/search_plans, no mention of the availability requirement or the pattern constraint. 'One currently available eSIM' is the only indirect signal, which is thin for a tool whose sole input gates everything.

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?

Starts with a specific verb and resource ('Get a link ... to review and buy one currently available eSIM') and immediately delimits the return value ('This only returns a URL'). The scope statement together with the explicit negatives makes it trivially distinguishable from get_plan and search_plans, which retrieve plan data rather than a purchase link.

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?

The description makes the usage context clear (a customer-facing review-and-buy link for a single available eSIM) and rules out side effects, so an agent knows this is the hand-off step before purchase. It never names an alternative sibling or states a when-not condition explicitly, so it falls short of a 5.

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