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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds genuinely useful context beyond that: the result is a PDF download link, the invoice content is immutable after booking because it is reported to tax authorities, and the API key needs access to this specific app. Minor gap on pagination/expiry of the link, but strong for an annotated read tool.

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 key fact (invoice as PDF link) and each subsequent sentence earns its place: return format, immutability constraint, and auth requirement. Slightly wordy with some redundancy between the first two sentences, but no filler.

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 one-parameter, read-only tool with annotations covering safety and no output schema, the description supplies what an agent needs: what is returned (PDF link), the immutability constraint, and the auth prerequisite. Nothing critical 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 description coverage is 100% and the single trip_id parameter documents itself ('Booking number from list_trips'). The description adds no parameter-level detail, so the default baseline of 3 applies – the schema does the heavy lifting.

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 and resource ('Invoice of a booking as a PDF download link') and specifies the concrete return format (PDF link). An agent can distinguish this from kiwi-com_get_trip or list_trips 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?

Usage is implied by the name and the phrase 'invoice Kiwi.com shows at the bottom of the booking page', but there is no explicit when-to-use or when-not-to-use guidance and no named alternative. The auth prerequisite ('Cotlet API key with access to this app') is stated, which helps invocation.

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