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

With no annotations, the description carries the full behavioral burden and does most of it well: it discloses that the link is Stripe-powered but self-hosted, that the buyer must confirm via a 6-digit emailed code, that nothing is ordered until confirmation, and that no account is required. It omits operational details like link expiry, rate limits, or what happens on abandoned checkouts.

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?

The core action and the 'give the url to the user' instruction are front-loaded, which is the right structure. It runs six sentences and the final sentence about one-tap install/QR codes is largely consumer-facing color rather than guidance the agent needs to select or invoke the tool.

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 no output schema, the description correctly compensates by explaining the return value (a url to hand to the user) and the end-to-end flow the agent must narrate. Nothing an agent needs to call this tool correctly 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 description coverage is 100%, so every parameter is already documented in the schema, giving a baseline of 3. The description adds meaning only for email (pre-fill + delivery target) and says nothing about currency or plan_id beyond the schema's own wording.

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?

The description opens with a precise verb+resource ('Create a secure payment link ... for a Siima eSIM plan') and immediately scopes it to siima.online, distinguishing it from the read-only siblings (search_esim_plans, get_esim_plan, list_destinations). An agent can tell this is the only tool that initiates a purchase flow.

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?

It states the operational context clearly ('Give the returned url to the user to complete payment') and implies the plan_id must come from a prior search, but it never explicitly names the sibling to call first (search_esim_plans) or states when-not to use it. Clear context, no explicit exclusions.

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