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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description is consistent with that ('WITHOUT placing an order'). Beyond the annotations it adds real context: it surfaces the credit debit that a subsequent create_order would incur, and notes the extra travel-eSIM return fields (unlimited, data_gb). It stops short of stating error/expiry behavior for an invalid or stale price_token, which is the main remaining gap.

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 key constraint ('WITHOUT placing an order') is front-loaded and the whole thing is a handful of tight sentences with no filler. It is dense with parentheticals and enum-like asides, which slightly taxes parsing, but every sentence carries decision-relevant information.

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 an output schema present, return values needn't be spelled out, and the description covers the workflow gating, both auth personas, all three verticals and the eSIM-specific extras. What it omits — behavior on expired/invalid tokens or partial failures — is secondary but would help for a tool whose only required input is an opaque token.

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 90%, so the baseline is 3; the description earns a bump by explaining that vertical type is inferred from price_token/catalog_id so the type param is often unnecessary, which is a semantic shortcut the schema only partially conveys. It does not add much on the other nine parameters, which the schema already documents well.

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?

Starts with a precise verb+resource ('Returns the price breakdown') and immediately scopes it ('WITHOUT placing an order'), which separates it from create_order and the other write siblings. It also declares it covers every vertical (top-up, travel eSIM, gift card), so an agent knows this single tool spans cases it might otherwise split across siblings.

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?

Explicit conditional routing: required for PRO credits because it shows the debit before create_order, optional for guest/consumer payment_link where guests can create immediately. It ties the decision to concrete states (checkout_mode=payment_link vs credits) rather than leaving the agent to infer, and names the follow-up tool (create_order).

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