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

Annotations mark this as a non-read-only, non-destructive, non-idempotent write; the description adds genuinely new context: no account or key required, nothing is reserved, and a plan_url is returned for the traveller to open and save. It does not warn that repeated calls create duplicate plans, which is the main gap given idempotentHint=false.

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?

Well front-loaded: purpose, then prerequisites, then how to pass stops, then return value, then the booking exclusion. Slightly padded by the redundant 'Give the traveller that link' right after describing plan_url.

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 compensates by naming the return value (plan_url) and telling the agent what to do with it, which is exactly what a caller needs. Nothing required to invoke or hand off the result 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%, so baseline is 3. The description restates what the schema already documents (stops in order, arrival/departure dates, optional activities) without adding format or constraint detail beyond it.

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?

States a specific verb+resource ('save a trip plan') and explains the concrete outcome: handing a traveller an editable itinerary plus a plan_url instead of a wall of text. It is unmistakably distinct from the visa/schengen siblings.

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?

Explicit trigger ('after you have planned a trip with someone') and an explicit exclusion ('Do not use it for bookings: it records a plan, it does not reserve anything'). The agent knows both when to call it and when not to.

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