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

Annotations only cover the safety profile (readOnly, openWorld, non-destructive). The description adds non-obvious behavioral contract: the response contains a list plus a hidden uprn and display_address, uprn must never be surfaced to the user, the agent must do the matching itself, and the values feed into the next tool. That is meaningful context beyond the structured fields.

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?

It is a single dense paragraph, but it is front-loaded with the usage trigger and nearly every clause carries operational instruction (question phrasing, matching, list fallback, uprn handling). Slightly run-on, but not padded.

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 an output schema present, return values need no explanation, and the description still covers the full usage loop: collection, matching vs. disambiguation, and the handoff of uprn/display_address to downstream tools. An agent has everything needed to call and act on it correctly.

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% for the single postcode parameter, so the baseline is 3. The description nonetheless adds real semantics beyond the schema: house number/name is deliberately NOT a parameter and must be collected in the same question and matched client-side against the returned list, which clarifies how the one-parameter design is meant to be used.

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 gives a specific verb and resource ('find the exact property' for a UK postcode) and clarifies the granularity rationale (broadband availability differs per property). It doesn't explicitly name or contrast the sibling tools (check_if_overpaying, find_broadband_deals, get_deal_details), so it stops short of top-tier sibling differentiation, but the tool's role as the address-lookup entry point is unmistakable.

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 states precisely when to use it (postcode in hand, exact property needed) and gives explicit branching: ask for postcode + house number in ONE question, self-match and proceed when the user already identifies the property, and only render the numbered list when the match is ambiguous or postcode-only. This is a full when/when-not/alternative specification.

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