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

Annotations already declare readOnly, idempotent and non-destructive, so safety is covered. The description adds genuinely useful behavior beyond that: results carry counts, and only areas that actually have accommodation in the index are returned (an implicit coverage limit). A minor gap is that it doesn't say whether the area names are the exact values search_hotels expects as filter keys.

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?

A single sentence, front-loaded with 'Use to', that carries purpose, sequencing and an example user question with 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 zero-param, read-only lookup with annotations covering the safety profile and no output schema needed, the description supplies everything required to select and call it correctly, including the ordering relationship with search_hotels.

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?

The tool takes zero parameters, so per the baseline this scores 4. There is nothing for the description to disambiguate beyond what the empty schema already communicates.

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?

Specific verb ('discover') plus concrete resource ('which parishes and localities have accommodation in the index') with the geographic scope named. It also differentiates itself from search_hotels, which is the sibling an agent would otherwise confuse it with.

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?

States exactly when to reach for it: before filtering search_hotels by area, or to answer a 'where can I stay' question. The alternative (search_hotels) and the condition that selects it are both named, so no inference is required.

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