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

Annotations already declare readOnlyHint=true and openWorldHint=false. The description adds valuable context: returns yes/no plus counts and examples, and implies it's a quick check rather than exhaustive. No contradictions. Could mention rate limits or auth scope, but still strong.

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 concise sentences with every part earning its place. Front-loaded with the primary action and examples, followed by referral to siblings. No redundant or filler text.

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 simple read-only tool with 2 parameters and no output schema, the description completely addresses what the agent needs: purpose, return values, and guidance on when to use alternatives. No gaps given the context signals.

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 coverage is 100% with clear descriptions as ISO codes. The description reinforces the country parameter via examples but adds no new details beyond schema. Baseline 3 is appropriate since schema already fully documents parameters.

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 uses specific verb+resource ('Check whether we cover a destination') and provides example queries, making the purpose immediately clear. It also distinguishes from sibling tools by mentioning alternatives for full lists.

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?

Explicitly states when to use this tool ('before choosing a plan') and directs to alternatives ('Use search_esim_plans or find_cheapest_plan for the full list'). Provides concrete example questions for typical use.

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