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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so safety is covered. The description adds real value beyond them: the exact returned fields, the edge case that Airalo shows the bar only when available and returns usage_available=false with no numbers otherwise, and the auth requirement (Cotlet API key with access to this app).

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?

Three sentences, front-loaded with the returned data before the edge-case caveat and the auth note. No filler, though the 'data bar from My eSIMs' phrasing is a bit of an aside that could be tightened.

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?

No output schema exists, so the description must convey the return shape, which it does (total/used/remaining/expiry, usage_available=false fallback). Auth and the missing-bar behavior round it out; a single-param read tool is adequately covered.

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?

Only esim_id, and schema coverage is 100% with the schema itself noting 'eSIM ID from list_esims.' The description references 'an eSIM' but adds no format or sourcing detail beyond the schema, so the 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?

States a specific verb (get) and resource (data usage on an eSIM), plus the concrete payload: total, used, remaining data and expiry date. It is distinguishable from siblings like airalo_get_esim or airalo_list_esims, though it doesn't explicitly name a sibling to contrast against.

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 is implied (check remaining data/expiry for an eSIM) rather than stated with when-to-use vs alternatives. There is no explicit guidance on when to prefer this over airalo_get_esim or when the eSIM must already be installed/active, so an agent must infer the trigger.

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