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

Despite the readOnlyHint=true annotation, the description clearly explains the behavioral nature: it hands off to an external shop, returns buy_url, no account is needed, the eSIM is emailed after payment. This adds substantial context beyond what the annotations provide, covering the interaction model and post-payment fulfillment.

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 three sentences, front-loaded with the core action, and each sentence adds distinct value: handoff behavior, return values, and explicit exclusions. Zero 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?

Complete for this tool. It covers what the tool does, what it returns, prerequisites (no account needed), fulfillment (email), and limitations. With an output schema also present, no critical information is missing for an agent to call it correctly.

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 documents both parameters (language and product_id). The description does not add syntax or format details for the parameters, so baseline 3 is appropriate.

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 (hand off to shop), resource (roamflat shop checkout), and scope (buy one plan). This is clearly distinguishable from sibling tools get_plan_details and search_esim_plans, which are for browsing/retrieval rather than initiating a purchase.

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 implies usage context (you use this to complete a purchase after selecting a plan) and explicitly rules out adjacent capabilities, stating there is no in-chat order tracking and no discount-code field. However, it doesn't explicitly name alternatives or state when not to use this tool versus browsing tools.

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