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

Annotations already declare readOnlyHint, idempotentHint and non-destructive/closed-world, so the safety profile is covered. The description adds useful behavioral context beyond that: it describes the shape of the response (grouped by service, USD, with overage rates and features), which matters because no output schema exists.

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 tight sentences, zero waste. The content/return shape is front-loaded and the filtering advice follows, so an agent gets the payload description before the optional narrowing tip.

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 return-value burden and does so adequately (plans, prices, USD, grouping, minutes/chats, overage rates, features). For a simple two-parameter read-only lookup with full annotation coverage, this is close to complete.

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 both the 'service' and 'billing_cycle' parameters are already fully documented with examples and enum values. The description only restates that filtering is possible and adds the motive ('keep the answer short'), which is baseline value over 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?

The description names a specific resource (current plans and prices in USD) and enumerates what it returns (included minutes/chats, overage rates, features, grouped by service). It is clearly distinguishable in intent from siblings like get_company_info or list_services, though it does not name an alternative explicitly.

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?

The second sentence gives actionable guidance ('filter by service or billing cycle to keep the answer short'), which implies when to narrow results, but there is no explicit when-to-use-vs-alternatives or exclusion guidance against the sibling tools.

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