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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds the context that it returns 'current price', but it does not disclose other behavioral aspects like response size, error conditions, or freshness guarantees. With annotations present, this meets the minimum viable bar.

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 a single, efficient sentence with no wasted words. It is front-loaded with the key action ('Full details') and the object ('one eSIM plan'), making it immediately scannable.

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?

This is a simple, read-only get-details tool with one well-documented parameter, an output schema to describe return values, and annotations declaring its non-destructive nature. The description, combined with structured data, provides enough context for an AI agent to select and invoke this tool correctly.

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 schema provides 100% coverage for the single parameter, identifying plan_id and instructing that it comes from search_esim_plans. The description's phrase 'one eSIM plan' loosely reinforces the singular nature of the parameter, but adds no substantive meaning beyond what the schema already gives. 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?

The description 'Full details of one eSIM plan, including current price' clearly identifies the action (retrieve full details), the resource (eSIM plan), and the scope (one plan). It is specific enough to distinguish from sibling tools like search_esim_plans, which lists plans rather than returning details for a single one.

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 implies the tool is for fetching details of a specific plan, and the schema's plan_id description ('plan_id from search_esim_plans') provides a useful prerequisite by indicating where to obtain the identifier. However, it does not explicitly state when not to use this tool or name alternatives.

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