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

Annotations already establish read-only, idempotent, non-destructive behavior, so the description's job is to add result semantics — and it does, disclosing cheapest-first ordering, throttling rules, hotspot policy, uncovered countries, and checkout availability. This is substantive context beyond the annotations, though it does not discuss pagination or empty-result behavior.

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 when-to-use guidance is correctly front-loaded, but the return-value sentence is a long comma-chained list in a single dense paragraph. Given there is no output schema the detail is earned, yet splitting it or trimming the enumeration would improve scannability.

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 takes on the burden of describing the response and does so thoroughly (price, data allowance, validity, networks, link, checkout status). All six optional parameters are meaningful and the zero-required-parameter design is implicitly clear from 'Leave out to search every destination' plus the schema.

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 interpretive framing: trip_days means only plans valid for the whole trip, and min_gb means the data actually needed, plus examples of country/region values. That clarifies intent of the filters rather than merely repeating the schema.

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 ('search and compare travel eSIM data plans') and frames it around the user question it answers. It is clearly distinguishable from siblings such as get_plan (single plan detail) and list_destinations (destination discovery).

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 concrete trigger scenarios: choosing a travel eSIM, finding the cheapest plan, comparing plans, or avoiding roaming charges. It also tells the agent which inputs to supply. It stops short of naming when to prefer a sibling (e.g. get_plan for a known plan), so it is clear context without explicit exclusions.

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