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

With no annotations, the description carries the full behavioral burden. It usefully discloses that answers are contingent on passport and entry route, and the informational framing implies a read-only lookup, but it says nothing about the shape of the answer (per-route rules, cost currency, processing steps) beyond the vague 'how'.

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?

Two sentences with no filler, and the scope statement is front-loaded before the constraint. It is efficiently sized, though the second sentence is doing double duty as both justification and parameter guidance.

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 two-parameter lookup with no output schema and no annotations, the description is serviceable but thin. It does not resolve the destination-vs-entry-route ambiguity or hint at what a qualifying answer contains, which matters because nothing else in the structured data fills that gap.

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 0% for both parameters, so the description must compensate. It does explain why both are required (rules vary by passport and entry route), giving passport clear meaning, but 'destination' is never defined relative to 'entry route', leaving genuine ambiguity about what value to pass.

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 informational resource — whether and how a stay can be extended, including duration and cost — which distinguishes it from siblings like visa_lookup and passport_power. It stops short of explicitly contrasting itself with those siblings, so it is clear but not fully differentiated.

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?

Usage is implied: this is the tool to consult for extension questions, and the description notes results vary by passport and entry route. However, it never states when to choose it over visa_lookup or list_destinations, nor any exclusions, leaving the agent to infer routing between siblings.

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