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

Annotations already cover read-only, idempotent, non-destructive, closed-world behavior, so the bar is lower. The description adds genuinely useful non-schema facts: UK-only coverage, free cost, and that the key is a UPRN rather than an address. It does not explain what max_drilldowns does or the latency/cost tradeoff it controls.

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 short sentences, front-loaded with purpose and immediately followed by routing and prerequisites. The 'UK only. Free.' fragments are terse but earn their place as scope/cost constraints; nothing is wasted.

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 explained. Combined with annotations, the description covers scope, cost, key type, and acquisition workflow. The only real gap is the unexplained max_drilldowns control on a tool whose depth it likely governs.

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 0%, so the description must carry parameter meaning. It handles uprn well (not an address; how to obtain one) but says nothing about max_drilldowns beyond the schema's default, leaving the second parameter's semantics undocumented in both places.

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 resource and scope: 'Sold-price history for a property, with per-sale detail.' It names the sibling it overlaps with (transactions_by_uprn) and the distinction is immediately usable, so an agent can separate the two 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?

Explicitly routes the agent: use transactions_by_uprn for raw HMLR rows, and this tool when per-sale detail is wanted. It also gives the prerequisite workflow (address_autocomplete then address_resolve to obtain a UPRN), which is exactly the when/how guidance most tools omit.

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