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

Annotations already declare readOnlyHint=true/openWorldHint=true and are not contradicted — this tool only mints a URL and mutates nothing server-side. The description adds genuinely useful behavior the annotations cannot convey: accepted payment methods, optional discount code, no-account requirement, post-payment email delivery, and the absence of in-chat order tracking.

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-loaded with the core action and return value, then layered with payment and delivery details. Slightly heavy with secondary facts (payment methods, discount code, email) but every sentence is relevant to setting customer expectations.

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 not be explained, yet the description helpfully names buy_url, plan name, and price anyway. Combined with annotation coverage and a simple two-parameter schema, the definition gives the agent enough to call it correctly; only explicit sibling routing 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 both parameters (product_id, language) are fully documented in the schema and the description adds no new syntax or format detail. The mention of an 'optional discount code' is not a parameter at all, so it adds no semantic value for invocation.

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 states a specific verb and resource — handing the customer to the IbiPoint shop to buy one plan and returning a buy_url — which is unmistakably different from the lookup-oriented siblings get_plan_details and search_esim_plans. An agent can identify this as the conversion step without opening any schema.

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 establishes clear context (buying one plan, no account needed, eSIM emailed after payment) that implies when to invoke it after plan discovery. It stops short of explicitly naming the sibling tools or stating 'call after search_esim_plans', so the routing guidance is inferred rather than spelled out.

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