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

Annotations already declare readOnly/openWorld/non-destructive, and the description adds real value beyond them: the auth requirement (Cotlet API key with access to this app) and the shape of each item (data amount, validity days, USD price, rechargeable flag). It does not discuss rate limits or pagination, but the safety and auth profile is well covered.

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?

Front-loads purpose and scope, then return fields, then the buy_esim linkage and auth note. Slightly padded ('which Airalo shows under Additional information') but every sentence conveys usable 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 no output schema, the description helpfully enumerates the returned fields and adds an auth prerequisite. For a single-parameter read tool with annotations covering safety, this is complete enough; only the missing alternative-tool guidance and pagination/rate-limit details keep it from 5.

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% and destination is fully documented in the schema, so the schema carries the burden. The description restates 'a country or region' without adding syntax or format details, 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 (search) and resource (eSIM packages from the store) scoped to a country or region, and differentiates from siblings like list_topup_packages and get_esim by emphasizing store-listed packages for a destination. An agent can tell what it retrieves 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?

Gives clear operational context: use the returned package_id with buy_esim, which ties the search to a downstream flow. However, it never contrasts against the sibling airalo_list_topup_packages, so the when-not (searching add-on top-ups) is left to inference.

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