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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile needs no restating. The description instead adds genuinely non-obvious behavior: the three-valued outcome and the meaning of 'by_arrangement' (travel terms and timing agreed by phone), which an agent could not infer from the 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?

Three sentences, front-loaded with the trigger condition, then input tolerance, then return values. The example place list is dense but each entry illustrates a distinct case type (city, district, resort, village, out-of-region town). No filler wording.

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 an output schema present, the description need not enumerate return fields, and it still supplies the interpretive key for the three statuses plus the accompanying page URL. Combined with annotations and full schema coverage, an agent has everything needed to invoke and interpret this tool correctly.

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 coverage is 100%, so a baseline of 3 would apply on schema alone. The description exceeds that by disclosing that the place argument tolerates Bulgarian, Latin and Russian spellings, which clarifies accepted input forms beyond the schema's example strings and directly affects how an agent should pass user text.

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 a specific verb and resource in user-question terms ('asks whether Kanal Varna comes to a specific city, district (квартал) or village') and enumerates the place types it covers. It is clearly distinguishable from siblings like get_prices, get_faq or find_service, which do not answer coverage questions.

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?

The opening clause 'Call this when the user asks whether...' gives an explicit trigger plus concrete example inputs ('Младост', 'Аспарухово', 'Добрич'). It stops short of stating when NOT to use it or naming the sibling to use for adjacent questions (e.g. pricing or booking), so it falls just below a full 5.

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