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

Annotations declare a non-read-only, non-destructive, non-idempotent, open-world write, and the description adds meaningful behavior on top: nothing is charged until payment on the link, links must be passed on 'exactly as returned', availability of PayPal may vary per order, and confirmations come only from a prior confirmation_required result after the user saw each text. It does not warn that repeated calls create separate orders despite idempotentHint=false, which is the one behavioral gap.

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?

The trigger condition is front-loaded and the important constraint (no charge until payment) sits early. The second sentence is long and packs return details, input shapes, and the fallback tool into one block, which is dense but almost entirely load-bearing.

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 9-parameter transactional tool with an output schema, the description covers preconditions, charge timing, input shape alternatives, and language/currency effects on returned names and links. The only omission an agent could stumble on is the absence of a retry/idempotency caution for this non-idempotent order-placement call.

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 baseline is 3, but the description adds semantics the schema lacks: items and plan_id+quantity are mutually exclusive input styles, items is capped at 5 plans / 10 eSIMs in total, and expected_unit_amount applies only after a price_changed result. The quantity 'one per traveller' intent and currency dependence are also reinforced in prose.

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 outcome: 'places the order on their account and returns two payment links', then enumerates what the links support (cards, Apple Pay, Google Pay, local wallets, PayPal) and what comes back (total, discount, order number). This is clearly distinguishable from sibling get_buy_link, which is named as the fallback for unconnected accounts.

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?

Gives an explicit trigger ('When the user decides to buy'), a precondition ('their Simvito account is connected'), and a named alternative for the negative case ('If the account isn't connected, use get_buy_link instead'). It also directs the agent to obtain plans from search_plans or plan_trip, so the upstream tool chain is clear.

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