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

Goes well beyond the readOnly/idempotent annotations: pd_status is always 'unclear', unresolved restriction evidence returns PD_EVIDENCE_UNAVAILABLE, nearby/null distances never prove containment, and source freshness is unverified. The limitations list (no legal applicability, no current-law version, no full-boundary intersection, no condition verification) is exactly the caveat context an agent needs.

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?

Labeled sections (Purpose / When to use / Returns / Limitations / Parameter guidance / Chaining) make it scannable and front-loaded. It is long, but nearly every sentence carries a distinct constraint; minor trimming possible in the returns list.

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?

The description covers usage, output semantics, failure mode, all major limitations, parameter expectations, and cross-tool chaining via site_ref. An output schema exists but the description still tells the agent how to interpret the deliberately non-committal result, which is the key risk for this tool.

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 already 100%, but the description adds real guidance: supply a full address/postcode and a concrete proposal phrase including use, works, and known dimensions, plus the rule that site_ref must be passed unchanged to reuse the canonical site. This meaningfully exceeds the schema text.

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 deliverable verb: prepare an England permitted-development evidence checklist with a tentative class hint, explicitly not confirming a legal route. The scope (England only, tentative not definitive) is stated up front, distinguishing it from raw-constraint siblings.

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?

Gives three concrete trigger questions (rear extension, Class E shop to flats, Article 4 loft conversion) and names the alternative 'use check_planning_constraints when you only need raw constraints'. Both when-to-use and a routing rule to a sibling are present.

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