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

Annotations already establish readOnlyHint=true and openWorldHint=false, but the description adds real behavioral context: prices are returned in RUB, normalized to one price per payment method, and ordered local-first. It does not mention pagination or result limits, which keeps it from a 5.

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?

Two compact sentences, zero filler, with the core resource and price semantics front-loaded before the ordering detail. Every clause carries information an agent can use.

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 usefully discloses return semantics (currency, per-payment-method pricing, ordering). For a read-only list tool with full schema coverage this is nearly complete, though it omits any hint of result volume or pagination.

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 days, min_gb, and country are fully documented in the schema, making 3 the correct baseline. The description adds currency context (RUB) but nothing about how filters interact or parameter formats beyond what the schema states.

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 ('List eSIM data plans for a country') and adds scope detail (final prices in RUB, one price per payment method). It distinguishes itself from compare_prices only implicitly via the price/ordering language, never naming the sibling, so it falls short of a 5.

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?

No when-to-use or when-not-to-use guidance is given, and the obvious alternative (compare_prices) is never mentioned. The clause about local vs. regional ordering describes output, not usage, so the agent must infer the tool's place in the workflow.

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