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

With no annotations, the description carries full burden. It discloses real-world effects (writing a formal order, connecting to real payment flow), failure modes (ok=false may mean order created but payment link failed, do not retry), and required user communication (provide paymentUrl as-is, remind order won't ship until payment). This goes far beyond basic mutation disclosure.

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 description is structured with a clear opening statement, numbered prerequisites, and explicit post-conditions. Though longer than average, every sentence provides necessary safety or correctness information for a high-stakes financial action, and the content is front-loaded with the core purpose.

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?

Given the tool's complexity (7 parameters, real money, no annotations, no output schema), this description covers prerequisites, parameter validation, return handling (paymentUrl, ok/error), and user-facing instructions. It leaves no critical gaps for safe invocation.

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?

Although schema already covers all 7 parameters (100% coverage), the description adds crucial constraints: productId and spec must come from query tools, quantity must match user confirmation, email/userName are mandatory, paymentMethod should be explicitly asked rather than defaulted. This enriches parameter semantics beyond the schema.

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 clearly states the tool creates a real eSIM order and returns a payment link (LinePay or ECPay). It explicitly distinguishes itself from the sibling read/search tools and emphasizes this is a real transaction, not a simulation.

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 provides explicit prerequisites referencing sibling tools (search_esim_plans/recommend_esim_plan/get_esim_plan_detail), mandates user confirmation and informed consent, and specifies when it should not be used (not for simulation/estimation). This gives clear when-to-use and when-not-to-use guidance.

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