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

Annotations already establish readOnly, idempotent, open-world, non-destructive behavior, so the safety profile is covered. The description adds genuine value by disclosing the ESIM_NOT_TOPPABLE failure condition tied to eSIM state, which the annotations cannot express. It stops short of describing pagination or the limit parameter's effect.

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 tightly written sentences, front-loaded with the resource and scope, then the error condition. No wasted words, though the parenthetical could be integrated more cleanly.

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 carries the return-value burden; 'with your price' hints at the payload and the error code is given, but list shape, ordering, and how limit affects results are left unstated.

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 only 50% — iccid is documented but limit is not. The description says nothing about either parameter beyond 'ONE eSIM', so it fails to compensate for the undocumented limit/cap behavior.

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+resource (top-up packages for an eSIM), scopes it to ONE eSIM, and notes the dependency on provider and location. This distinguishes it from catalog-wide siblings like search_packages, though it doesn't name them explicitly.

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 'ONE eSIM' framing and the provider/location dependency imply when this tool is appropriate versus a broad package search, and the ESIM_NOT_TOPPABLE note signals an eligibility precondition. However, no alternative tool is named and no explicit when-not-to-use guidance is given.

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