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

Annotations already mark it read-only and open-world, so the description wisely spends its words elsewhere: per-call pricing ($0.002 USDC, x402 on Base/Solana/Arc), that failed calls are not charged, that currency depends on visitor region, and that the order is Hostelworld's not a sort you control.

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?

One dense, front-loaded paragraph: what you get, in what order, what format the inputs take, the key limitation, then the price. Every clause carries distinct information and nothing is repeated.

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 covers scope, input format, result cap, ordering, absence of availability data, and billing model. Return values need not be explained further since an output schema exists, yet the field list is still supplied as a convenience.

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 the schema already documents all four parameters including per-parameter examples. The description reinforces the URL-slug convention (europe / germany / berlin) but adds no format or constraint detail beyond what the schema states. Baseline 3 applies when the schema carries the load.

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 resource (hostel listings for a city), names the source (Hostelworld's public city page), caps the result set (up to 30, Hostelworld's own order), and enumerates the returned fields. This is enough to distinguish it from sibling hotel tools like booking_com_hotels or google_hotels_price without opening any 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?

'No live availability for dates' explicitly draws the boundary against date-based booking siblings, and 'up to 30, Hostelworld's own order' sets expectations. It does not name a specific alternative tool to use instead, so it stops short of a full when/when-not routing statement.

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