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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so the safety profile is covered. The description adds substantive scope beyond that by enumerating exactly what is returned (promos, crossed-out/announced prices, order fees, commitment total, roaming, suitability overview), which tells the agent the depth of the response. No mention of error or missing-id 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?

Two sentences, front-loaded with what the tool returns before the usage trigger. The long enumeration of return contents is dense but each item is informative; only slight trimming would be possible.

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 describing the return payload, and it does so thoroughly while also pointing to the source of the id. Complete enough for an agent to call correctly, though it could note behavior when the id is invalid.

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 both parameters (plan_id, language) are already documented, which sets the baseline at 3. The description reinforces plan_id's provenance ('the id search_mobile_plans returned') and hints at a localized overview via 'PriceBee's overview', but adds no syntax or format detail beyond 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?

Starts with a specific verb+resource ('One mobile plan in full') and immediately enumerates the payload (contract options, prices, fees, roaming, EU calls/SMS, suitability overview). This clearly distinguishes it from the sibling search_mobile_plans, which is framed as the source of the id rather than the detail fetcher.

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?

'Use it when the user asks about a specific plan or wants the fine print before choosing' gives clear usage context, and the reference to 'the id search_mobile_plans returned' implicitly routes the agent through the search tool first. However, it never explicitly states when NOT to use it or names search_mobile_plans as the alternative for browsing, so it stops short of a full 5.

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