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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so the safety profile is covered. The description adds genuinely useful behavior: the paid guide body is never returned, and an unknown slug produces an error rather than empty output.

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-loads the action and identifier, then the return contract and the error case, in a compact paragraph with no filler. The field enumeration is slightly list-like but earns its place given no output schema.

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 takes on the return-value burden and does so: it names the returned fields, states the boundary condition (no full guide), and documents the failure mode. Nothing needed to call it correctly 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 coverage is 100% and the single slug parameter is fully documented (pattern, maxLength, examples) in the schema itself. The description only restates that the slug comes from list_itineraries, adding no format or syntax detail beyond the schema — baseline 3.

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+resource (get one itinerary preview by slug) with explicit scope narrowing ('public preview', 'the complete paid day-by-day guide is never returned'). It distinguishes itself from list_itineraries by name, so an agent can route without opening a 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 clear intended uses ('describe a trip to the user', 'decide whether the full guide fits') and identifies list_itineraries as the source of the slug. It stops short of an explicit 'if you want all itineraries, call list_itineraries instead' exclusion, so it's clear context without full alternative routing.

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