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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description adds genuinely new context by describing the returned fields (plan count, cheapest monthly price, 5G flag), which the annotations cannot 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?

Two sentences, front-loaded with what the tool returns and followed by usage routing. Every clause earns its place, though the parenthetical country list partially duplicates the schema enum.

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 burden of explaining return shape and does so explicitly (per-operator plan counts, cheapest price, 5G presence). Combined with the usage handoff and the fully documented single parameter, an agent has everything needed to call it 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% and the enum already documents lt/lv/ee including the default. The description's parenthetical country list reinforces the enum but adds no syntax or semantics beyond it, so the baseline of 3 applies.

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+resource ('The mobile operators PriceBee compares') scoped to three named countries, and explicitly enumerates what each entry contains (plan counts, cheapest price, 5G availability). It also distinguishes itself from siblings by naming search_mobile_plans as a downstream consumer.

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 clear when-to-use framing ('questions about which operators exist, or to pick operator names for search_mobile_plans'), effectively routing the agent to the lookup-vs-search split. It stops short of stating when this tool is the wrong choice (e.g., when the user already knows the operator).

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