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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds meaningful behavior beyond that: results are cheapest first with live prices in USD, and if no single plan covers every country the tool returns one eSIM per country. It also implies a returned code that feeds into get_esim_plans. These are useful operational details that annotations alone would not convey.

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 the core purpose and then gives usage conditions and follow-up steps. The list of example hub cities is helpful but adds length; nevertheless, each sentence provides a distinct piece of information. It is appropriately sized for a search tool with a nuanced routing condition.

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?

There is no output schema, so the description must carry the return-value burden. It explains that results are plans on one QR code, cheapest first, priced in USD, with a fallback of one eSIM per country if no combined plan exists, and that a returned code is used with get_esim_plans. This is enough for an agent to invoke the tool and understand what comes back, though it does not describe the full response shape.

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 individual parameters are already documented. The description adds semantic value by explaining that 'via' and 'to' must both be covered by a single plan, and that an optional second stop is supported. This clarifies how the parameters interact to produce a combined-coverage result, which is more than the schema 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 states a specific verb and resource: finding Slashtel travel eSIM plans that cover both a transit hub country and a destination on one QR code. It distinguishes this from generic plan lookup by emphasizing combined layover-and-destination coverage, cheapest-first ordering, and live USD pricing. An agent can tell exactly what this tool does without opening the 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?

The description gives clear when-to-use guidance: trips with a connection through hubs such as Dubai, Doha, Istanbul, Singapore, and others, where data is needed during the layover and on arrival. It also explains the follow-up path with get_esim_plans and create_checkout_link, which helps an agent sequence calls. It stops short of explicitly saying when not to use this tool versus a single-destination search, so it is strong but not exhaustive.

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