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

Annotations cover only read-only and open-world traits; the description adds substantial information they don't carry: approximate result count (~35 hotels), currency behavior tied to the visitor region (and that the currency is reported in the output), the metered cost ($0.002 USDC via x402 on Base/Solana/Arc), and that failed calls are not charged. That payment and currency context is exactly the kind of behavioral detail an agent needs before spending a paid call.

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-loaded with the core resource and return fields, and every clause (result count, currency, non-dated caveat, pricing) earns its place. The first sentence is a very long run-on packing seven output fields into one clause chain, which slightly hurts scannability but wastes no words.

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?

An output schema exists, yet the description still summarizes the key fields an agent would select on (rating, price, stars, URL) and adds non-schema context: approximate volume, currency semantics, the dated-vs-undated distinction, and the billing model. Nothing an agent needs to decide whether and how to call it 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 'city' parameter is already documented with examples in the schema, so the baseline is 3. The description adds only adjacent meaning (currency is chosen by visitor region, not a parameter) rather than further semantics for 'city' itself, which is acceptable but not additive.

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 ('trivago hotel prices for a destination') and enumerates exactly what comes back: hotel name, location note, lowest nightly price, guest rating out of 10 with review count, stars, URL, plus destination price facts. It also explicitly scopes itself against the obvious confusion ('not a dated availability search'), letting an agent distinguish it from dated availability lookups without opening the 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?

The phrase 'not a dated availability search' clearly signals the exclusion and implies the right use case (city-level price survey / destination cost benchmark). It does not, however, name any alternative sibling such as travel_booking_com_hotels, travel_kayak, or travel_google_hotels_price, so routing between the many hotel tools is still left partly to inference.

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