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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so safety is covered. The description adds genuinely new context: prices are in KRW, the result includes computed winners (lowest price, most data, longest validity, lowest price per GB), and each plan's page URL is returned.

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?

Two sentences, front-loaded with the verb and scope, and no filler. The attribute list in sentence one is long but each item is a real comparison dimension, so it earns its place.

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 a full output schema and rich annotations, the description only needs to frame scope and routing, which it does. The KRW currency note is a useful addition; nothing an agent needs to call this correctly 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 coverage is 100%, so the ids cardinality (2-5) and the lang enum are already fully documented in the schema. The description only restates that ids come from search_esims, adding minimal meaning beyond structured fields; baseline 3 applies.

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?

Specific verb (Compare), resource (esimoa eSIM plans), scope (2 to 5, by id), and the compared attributes are enumerated. It also names the sibling that produces the ids (search_esims), so an agent can distinguish it from search_esims, get_esim, and search without opening a 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?

It clearly establishes the precondition that ids come from search_esims and the 2-5 cardinality, which is exactly the context needed to invoke it. It stops short of saying when not to use it (e.g. single-plan lookup should use get_esim instead).

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