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

Annotations already declare readOnly/idempotent/non-destructive, and the description reinforces this correctly by stating it does not pay or place an order. It goes further with the post-purchase lifecycle (confirmation page, Install button, QR code, private eSIM link), though it does not address link expiry or whether repeated calls return an identical URL, which matters given idempotentHint=true.

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-loads the deliverable in the first sentence and follows with the outcome flow. The enumeration of payment methods is slightly extraneous to invoking the tool but is defensible as user-facing context; overall there is little waste.

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?

With 100% schema coverage, an output schema, and full annotations, the description supplies the remaining behavioral context an agent needs: what the link is for and what it does not do. Only link lifetime and idempotency semantics are left implicit.

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 description coverage is 100%, so the schema already carries the parameter documentation; baseline is 3. The description adds only one useful pointer, that plan takes the name exactly as get_plans returns it, which mildly reinforces the plan parameter without adding new syntax or constraint detail.

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 artifact: produces a checkout URL on esimpass.com with one plan pre-selected, and explicitly clarifies it is not a payment or order. This distinguishes it cleanly from siblings like get_plans (discovery) and fetch (retrieval).

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?

Provides clear workflow context (the traveller opens the link and pays, then gets an install page) and routes the agent to get_plans for the plan-name input format. It lacks an explicit when-not or a named alternative for other purchase paths, but the intended use is unambiguous.

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