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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds genuine context beyond that: the fare-type precondition, the fallback behavior of returning a reason, and the Cotlet API key/app-access requirement.

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 and reasonably tight, but the first two sentences restate the same idea (options for a new date plus per-option fees), and the 'Omio:' prefix adds no information. Minor redundancy only, not bloat.

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 in existence, the description carries the return-value burden and does so: alternate options with price difference and fee, or an explanation of why the ticket can't be changed. Combined with the annotations and 100% schema coverage, an agent has everything needed to call and interpret this tool.

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 booking_id and date are fully documented in the schema itself. The description adds nothing about their format or sourcing (it cites option_id, but that is an output value passed to change_booking, not an input here). Baseline 3 is appropriate.

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: for an exchangeable fare it returns the alternate travel options for a new date and their fees. It also disambiguates the sibling relationship by pointing at change_booking as the consumer of the option_id, so an agent can tell this apart from omio_change_booking or omio_get_booking.

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?

Clear eligibility context: online changes are only possible for exchangeable fares, and non-exchangeable fares return the reason instead. It also states the follow-up action (pass option_id to change_booking). No alternative tool is named for the ineligible case, which keeps it from a 5.

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