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

The annotations already declare readOnlyHint, idempotentHint, and no destructive effects. The description adds valuable behavioral context beyond annotations: the instruction to use `msisdn` in user-facing text and to not surface the internal `id` field. This is useful, non-obvious output-handling guidance.

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 concise and front-loaded: the first sentence summarizes the action, and the second sentence adds a focused, important clarification. Every sentence carries meaningful information without fluff.

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?

Given the tool's simplicity (no params) and the existence of an output schema, the description is complete for the agent's decision-making. It covers the key user-facing distinction (msisdn vs id) that goes beyond what the schema alone would convey.

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?

The tool has zero parameters, so the baseline is 4. The description correctly avoids inventing parameter details and instead explains the output fields, which is appropriate for a parameterless endpoint.

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 starts with a specific verb ('List') and resource ('the authenticated user's eSIMs'), and names the returned fields (status, balance, msisdn). It clearly distinguishes itself from siblings by focusing on listing multiple eSIMs for the current user, as opposed to get_esim or list_countries.

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 states what the tool does but does not explicitly compare it to alternatives like roamzy_get_esim. The context is clear enough to infer the primary use case, but it lacks explicit when-to-use/when-not-to-use guidance.

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