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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and a closed-world scope, so the safety profile is covered. The description goes beyond that by disclosing the result granularity (one entry per partner), what each entry contains (verified pickup facts plus a tracked booking link), and the empty-list outcome for uncovered cities. It doesn't mention pagination or partner-coverage caveats, but it adds real behavioral context.

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 compact sentences, both front-loaded with the essential scope and the failure mode. The '(read-only)' tag is redundant with the annotations, which is a minor waste, but nothing else is padding.

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?

An output schema exists, so return-value documentation is not required, yet the description still characterizes each entry usefully. Combined with the empty-result behavior and 100% schema coverage, an agent has enough to invoke it correctly; only explicit usage guidance 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%, including the slug/name examples and the did_you_mean behavior for unknown cities, so the schema already carries parameter semantics. The description adds no extra syntax or constraint detail about country vs city usage beyond restating 'cover a city'. 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 names the resource precisely ('car hire partners that verifiably cover a city') and the shape of the result (one entry per partner with pickup facts and a booking link). The verb is implied rather than stated, but an agent can tell instantly this is a car-hire lookup and not a stays or experiences lookup. No sibling overlaps, so explicit differentiation isn't needed.

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 is only implied: the agent infers this is the tool for finding car hire in a given city. There is no explicit when-to-use statement, no guidance on city vs country combinations, and no routing to any alternative (e.g., when a city has no car-hire coverage, what to do instead). The 'empty list' note is behavioral rather than a usage instruction.

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