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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description adds rich context beyond that: ~190 entries with Travel Pass first, alphabetical ordering of countries/regions, an exact-string guarantee for the search_esims country parameter, and disclosure that responses also surface PUL destinations. No contradiction with 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?

Despite being long, every sentence earns its place. Core purpose and trigger conditions are front-loaded, the (a)/(b)/(c) enumeration makes conditions skimmable, and the alternative-tool routing appears exactly where needed rather than in a separate section.

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 zero-parameter read-only tool with an output schema and safety annotations, nothing an agent needs is missing: return size, ordering, parameter-matching semantics, reverse-question answering, edge cases (uncommon destination names, empty search results), and routing to the sibling that covers region contents.

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?

With zero parameters, the baseline is 4, and the description earns above baseline by confirming 'No input parameters required' and by adding cross-tool semantics: the returned names are the exact strings to pass as the country parameter to search_esims. This meaningfully instructs the agent how to chain outputs into a sibling tool.

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 opens with a specific verb and resource: 'List every destination (country or region) the eSIMfinder catalog covers.' It also distinguishes itself from siblings by name, noting that search_esims consumes these names as the `country` parameter and that get_esim_finder_info handles region-bundle breakdowns.

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?

Usage guidance is explicit and structured: three concrete trigger conditions (a/b/c) tell the agent when to call this before search_esims, and a clear when-not instructs it to use get_esim_finder_info with topic='regions' instead for bundle contents. It even covers the no-results fallback case.

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