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

Annotations already declare readOnly/openWorld/non-destructive, so the safety profile is covered. The description adds an auth prerequisite ('Needs the user's Cotlet API key with access to this app') and describes the returned payload, which is valuable context beyond the annotations.

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 second sentence largely restates the first, repeating 'ICCID', 'package history'/'packages bought', and the renewals wording almost verbatim. The useful signal (auth + set_renewals sequencing) is diluted by this redundancy.

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?

For a single-parameter read tool with annotations and full schema coverage, the description covers return contents (since no output schema exists), usage context, and auth needs. Adequate, though the redundant phrasing wastes space that could carry more precision.

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 one parameter with 100% schema coverage, and the schema already explains 'eSIM ID from list_esims'. The description adds no new input semantics, 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 and resource ('Details of one eSIM') and enumerates the returned fields (ICCID, package history, rechargeable, renewals). It distinguishes clearly from the plural list_esims by emphasizing 'one eSIM', though it does not name list_esims 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?

Provides a concrete sequencing rule ('Use it before set_renewals'), which tells the agent when this tool is the right call. No explicit exclusions or alternate-tool routing are given, keeping it just short of a 5.

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