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

Annotations already declare readOnly/openWorld/non-idempotent/non-destructive, and the description adds substantial context beyond them: OGL v3 licence, attributes-only return with no determination, source data and provenance, SI normalisation of hydrological units, no-API-key access, concrete anonymous throttling (60/hour, 300/day per IP and session), key-based higher limits with anonymous fallback, and licence warnings.

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?

Purpose and scope are front-loaded in the first sentence, and the remaining sentences each carry operational value (licence, return shape, quotas). The 'TerraMCP is a Wrench AI service' branding sentence is the one low-value entry, but the whole remains compact and readable.

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 no output schema present, the description does the necessary work of saying results are attributes plus provenance and not a determination, and it covers access and quota constraints. It stops short of enumerating the returned attribute fields, but for this data-lookup tool it is complete enough to invoke 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 description coverage is 100%, so lat/lon/limit/radius_km are all already documented, and the description adds only the general notion of a bounding box around a point (already echoed in the schema). Baseline 3 is appropriate when the schema carries the parameter semantics.

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 (Find), a named resource (Natural England Sites of Special Scientific Interest), and the exact spatial scope (intersecting a bounded WGS84 box around an England point). This is clearly distinguishable from all the sibling data-source tools (bgs, ea, nrw, sepa, etc.) without opening any schema.

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 conveys the operational context (open data, no signup, anonymous rate limits) and a caveat that results are not a planning or ecological determination, which implies intended use. However, it never states when to pick this tool over an alternative sibling such as planning_entities, nor any explicit exclusions or prerequisites for a query.

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