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

Beyond the annotations (readOnly, idempotent, non-destructive), the description adds highly relevant behavioral context: the itinerary follows the OFFICIAL stages adapted to pace, an omitted `fecha_inicio` produces 'to be confirmed' dates, `mapa_url` is a real PNG that should be rendered immediately after the stage table, and the Spanish section requires asking for confirmation before quoting. This is exactly the kind of runtime behavior and interaction protocol an agent needs.

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?

The description is front-loaded with the core purpose, then systematically covers usage scope, parameter semantics, output behavior, and the confirmation workflow. There is no filler; the Spanish section earns its place by adding the pre-quote confirmation instruction rather than merely repeating the English text.

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?

The description is nearly complete for a 7-parameter tool with an output schema: it explains optionality, date behavior, output rendering, and the client-confirmation workflow. The main missing piece is guidance on how to obtain valid `camino_slug` and `poblacion_inicio_id` values, which would make first-time invocation fully unambiguous.

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?

With 0% schema description coverage, the description carries the burden and does it well for most parameters: it defines `ritmo` with exact km/day ranges, explains `km_max_etapa` as an explicit cap or cycling (~2x), specifies `fecha_inicio` format and the consequence of omitting it, and scopes `num_noches` to fixed-night requests. However, the required `camino_slug` and `poblacion_inicio_id` plus the optional `poblacion_destino_id` are left only to their names, with no guidance on where valid values come from.

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 opens with a specific verb and resource: 'Build a day-by-day Camino de Santiago itinerary' and enumerates the concrete outputs (walking stages, km per day, overnight towns, dates, route map image). It also defines the exact scope of questions it answers, such as 'any Camino itinerary, stage plan or "how many days from Sarria/Tui/Porto/Roncesvalles" question', which distinguishes it from the quoting/packaging siblings in this tool set.

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 description clearly states when to use the tool ('Use it for any Camino itinerary, stage plan...'), when to call it even without a confirmed date ('call it anyway'), and gives conditional parameter guidance (use `km_max_etapa` instead of `ritmo` for a cap or cycling; pass `num_noches` only when the client fixes the number of nights). It lacks explicit alternatives or 'when not to use' statements naming sibling tools, so it does not earn a 5.

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