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

Annotations already cover safety (readOnlyHint, idempotentHint, destructiveHint=false, openWorldHint=false), but the description adds material context the annotations do not: pricing is in euros per month unless price_period overrides it, data comes from operators' own sites and is refreshed daily, and the result's pricebee_url/order_url is the link to hand the user. That freshness, currency-interpretation and follow-up-link guidance is genuinely supplementary.

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?

Four sentences, front-loaded with the what/where and then usage, units and the actionable link. All sentences carry information, though the 'Set only the filters the user actually asked for' sentence and the link sentence sit awkwardly after the schema-facing content rather than being grouped.

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 has to carry return-value orientation, and it does: it explains price units, per-period caveat, data provenance/freshness and which URL to surface. It does not describe the shape of each result or pagination beyond the limit parameter, which is the main remaining gap for a 17-filter search tool.

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 every one of the 17 filters is already documented with enums and units, which sets the baseline at 3. The description reinforces price semantics ('per month unless price_period says otherwise'), which is useful since price_period is a result field not present in the schema, but it adds little else beyond what the schema provides.

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 states a specific verb and resource with explicit scope: mobile phone plans across every operator in Lithuania, Latvia and Estonia, as compared on PriceBee. It implicitly separates itself from list_mobile_operators and get_mobile_plan by framing itself as the multi-plan comparison search, though it never names a sibling to sharpen the boundary.

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?

It gives a clear use trigger ('whenever someone wants a mobile, SIM-only, prepaid or data plan, or to compare operators') and an operational caution to set only the filters the user actually asked for. It stops short of naming alternatives (e.g. get_mobile_plan for a single plan's details), so there is no explicit when-not guidance.

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