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

Annotations already cover readOnly/idempotent/non-destructive, and the description adds context beyond them: no stock is reserved, and the response includes a cheapest-match recommendation alongside price/validity details. That pre-empts an agent worrying that searching has side effects or requires a follow-up to compare prices.

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 purpose, then filters, then return shape, then routing alternatives — a logical order with no filler. The first sentence is long and list-heavy, but every clause is load-bearing; no sentence could be cut without losing information.

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 8 parameters, no output schema and 75% schema coverage, the description usefully summarizes the return payload (matching plans, price/validity details, cheapest-match recommendation) and the full call sequence around it. The only gap is that 'limit' behavior (pagination/cap of 50) and any default page size go unmentioned.

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?

The description adds genuine semantics the schema alone leaves ambiguous — 'days' is explicitly a minimum (trip length) and 'data_gb' a minimum, not exact — and maps unlimited and max_price_eur to filter intent. It does not mention the 'limit' or 'lang' parameters, which are the two with the least schema documentation.

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?

Opens with a specific verb+resource ('Find available travel data eSIM plans') and enumerates the destination granularity with concrete examples ('Japan', 'Tokyo', 'Europe', 'TR'). An agent can immediately distinguish this lookup/search tool from siblings like compare_plans and get_plan.

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?

Explicitly routes the agent: use get_plan to validate a chosen plan, then prepare_order; use list_destinations when a location is not recognized. It also states the key negative — 'without reserving stock' — so the agent knows this is a safe exploratory step before the purchase flow.

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