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

Annotations already declare read-only and idempotent behavior, but the description adds much more: the exact return fields (price EUR/VAT, data, validity, activation, purchase link), the language-insensitive matching behavior, the exclusion of regional/global plans under country names, and the matches/returned pagination semantics. This far exceeds what annotations alone convey.

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 description is logically organized: purpose, return fields, matching semantics, then pagination. Every sentence earns its place, though the regional/global explanation and examples make it slightly longer than strictly necessary. Overall it is dense but not bloated.

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, the description carries the full burden of explaining return values, and it does so thoroughly: plan attributes, matches/returned counts, and limit cap. It also covers the tricky matching behavior and filter semantics. An agent has everything it needs to invoke search_plans correctly.

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%, so the baseline is 3. The description still adds meaningful nuance: it explains destination matching beyond the schema examples (country name returns local plans, regional/global require region name) and clarifies limit/pagination behavior ('raise limit (max 40) to see the rest').

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?

The description opens with a specific verb-resource pair: 'Search travel eSIM data plans by destination name.' It clearly differentiates from siblings (get_plan and list_destinations) by framing this as a search-by-name operation and further specifying country vs. regional/global behavior, so an agent can tell it apart.

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 description gives explicit direction on when search_plans works: country names return local plans, while regional/global plans require searching the region's name or 'global'. It doesn't explicitly reference sibling tools as alternatives, so the when-to-use guidance is strong but the alternative-selection guidance is implied rather than stated.

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