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

Annotations cover read-only/open-world, and the description adds genuinely new operational context: free of charge, no API key required, and a concrete rate limit of 50 free-tool calls per IP per day. It also describes the returned sample's contents, which the absent output schema cannot convey.

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?

Three tight sentences, front-loaded with the purpose and then the routing decision, followed by cost/limit facts. Every clause carries information an agent needs; there is no filler.

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 one-parameter, annotation-covered, output-schema-less tool, the description covers purpose, alternative routing, cost, auth, rate limit, and the shape of the returned sample. Nothing required to call or interpret it is missing.

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 description coverage is 100% for the single parameter, so the schema already documents the English country name and the 'Germany' default. The description repeats that information without adding format, validation, or fallback behavior beyond it, so the baseline of 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 ('preview the shape and quality of eligibility data') and explicitly scopes itself as a sample rather than the full dataset. It names the sibling check_visa_free_eligibility as the full-data alternative, so an agent can distinguish the two without opening either schema.

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?

Gives an explicit when-to-use ('before paying', to preview shape and quality) and a when-to-use-the-other ('For full routes, conditions, dates and all sources use check_visa_free_eligibility'). Nothing about tool selection is left to inference.

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