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

Annotations already cover safety (readOnlyHint, destructiveHint=false), so the bar is lower. The description adds useful behavioral context: results become 'address-precise instead of postcode-wide' when uprn is passed, and clarifies that total_contract_cost is the whole-contract figure over contract_months – a semantic clarification not in the schema. It doesn't discuss rate limits or error behavior, keeping it from a 5.

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?

Three sentences, front-loaded with the when-to-use trigger before the parameter guidance. It is dense but each clause carries information; the only slight redundancy is restating address_label's purpose already in the schema.

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?

Given read-only annotations and an existing output schema (so return shape needn't be explained), the description covers selection (which deal), upstream dependency (deal_id from other tools), parameter intent, and a key field semantic (total_contract_cost). Nothing material for correct invocation is missing.

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 the schema already documents all four parameters thoroughly (including the 'never show this number' note on uprn). The description reinforces intended usage (pass deal_id from earlier result; postcode/uprn/address_label when known; total_contract_cost semantics) but adds little beyond the schema. 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?

The description states a specific verb+resource ('full details for one deal') and explicitly scopes it as 'ONE specific deal already returned by another tool', distinguishing it from siblings find_broadband_deals and check_if_overpaying. It also names the concrete detail fields returned (setup costs, price-rise terms, post-intro behavior, availability).

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 an explicit trigger ('Use when the user asks for more detail about ONE specific deal already returned by another tool') and names the upstream tools that supply the deal_id. The distinction from breadth tools is clear via 'already returned by another tool'.

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