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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description adds meaningful behavioral context: it returns a clickable URL, instructs the agent to render it as markdown, and warns about the trust-breaking price mismatch if currency is inconsistent. No contradiction with annotations.

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 front-loaded with purpose and includes only a short usage rule plus the currency critical note. It is slightly repetitive with the schema's currency property description, but the repetition is justified by how important the requirement is.

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 annotations, full parameter documentation, output schema, and clear relationship to search_esims, the description covers the essential context: when to use it, how to render the result, and the critical currency alignment. Nothing necessary for correct invocation 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 the input schema already documents sku, currency, and quantity. The description reinforces the currency-matching rule and adds the trust rationale, but it does not add substantial parameter meaning beyond what the schema already provides.

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 specific verb and resource: 'Generate a checkout URL for a specific eSIM plan.' It clearly distinguishes this tool from the sibling search/plan/info tools by tying itself to search_esims results and the checkout 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?

Usage guidance is explicit: 'Use only AFTER the user has chosen a specific plan from search_esims results.' It also gives a precise currency-matching rule with a concrete failure scenario, so an agent knows exactly when and how to invoke the tool correctly.

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