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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds genuinely non-obvious behavior: the verdict is computed server-side and must be presented verbatim, and each alternative's cost_24_months is the true cost over a 24-month window rather than a headline monthly price.

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?

Front-loaded with the usage trigger, then result-handling, then the one non-obvious parameter note. Dense but every sentence carries information; the quote_type sentence is mildly redundant with the schema enum description.

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?

An output schema exists so return values need not be enumerated, and the description still clarifies the cost_24_months semantics and the verbatim-presentation requirement. With annotations covering safety and the schema covering inputs, the remaining gap is minimal; cross-references to get_deal_details and search_addresses are present.

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 parameter (including quote_type's enum and the uprn/address_label handoff from search_addresses) is already documented in the schema. The description's only parameter guidance, the 'renewal_offer' case for quote_type, largely restates the schema, so the baseline 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 and resource: it compares the user's current or quoted price against comparable deals available at their address and returns a computed verdict with 24-month savings. It also names the sibling get_deal_details and how it differs (whole-contract totals), so an agent can distinguish it without opening schemas.

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?

Opens with an explicit trigger ('Use when the user asks whether their CURRENT broadband bill or plan, or a RENEWAL or retention offer...is expensive, competitive or worth switching from') and routes the adjacent case to get_deal_details. It also tells the agent how to act on the result ('present the verdict and figures verbatim rather than deriving your own').

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