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

Beyond readOnlyHint/openWorldHint, the description discloses cost (free), auth (no key), a concrete rate limit (50 calls per IP per day across free tools), and precisely what the response contains. It also surfaces the no-agency/intermediary policy caveat, which shapes how results should be presented.

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?

Front-loaded with purpose, then inputs, output, alternative, compliance note, and cost/limits — logical order with strong signal density. The bilingual legal disclaimer is boilerplate that occupies meaningful space, the only real bloat.

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?

With no output schema, the description compensates by enumerating the returned fields (visa-free status for ordinary passports, max days, route names, one source link). Combined with limits, defaults, and the sibling handoff, nothing material is missing for correct invocation.

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% and the schema already says the parameter is an English country name defaulting to 'Germany'. The description restates the same facts (English country name, default Germany) without adding format edge cases or semantics beyond the schema, 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 — preview the shape and quality of eligibility data — and immediately frames itself as a sample rather than the full lookup. The contrast with check_visa_free_eligibility is made explicit, so an agent can separate 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 (preview/sample) and an explicit alternative with the condition that selects it: 'For full routes, conditions, dates and all sources use check_visa_free_eligibility.' That is exactly the routing information an agent needs.

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