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

Annotations already cover the safety profile (read-only, idempotent, non-destructive), so the description's added value is the geometry semantics: any monument whose mapped area overlaps the search square is included, and distance is measured to the monument's reference point rather than its edge — a distinction that materially affects result interpretation. It also discloses the upstream source and a 1-credit cost. It does not say what happens when results exceed the limit.

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?

Front-loads the core action and ordering, then layers use cases, provenance, geometric caveats and cost. Dense but largely earning its space; 'Takes lat/lon' is the weakest phrase since the schema already makes that obvious.

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, the description compensates by naming the return fields, the sort order, and the distance metric. It is close to complete for a lookup tool, with the remaining gap being truncation behaviour when limit caps results and the required-vs-optional coordinate ambiguity.

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 and radius_m are already documented with ranges and defaults; the baseline of 3 applies. The description adds useful framing — that the coordinates define a search square and distances are to the reference point — but it does not resolve the discrepancy that the schema marks zero parameters as required while lat/lon are described as required, nor how radius_m shapes the search area.

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 and resource ('List scheduled monuments'), the geography ('around a point in England'), the ordering ('nearest first'), and the returned fields (date scheduled, area, official link). It does not name or distinguish itself from the sibling 'scheduled_monument_search', though 'around a point' implicitly signals a spatial query versus a name-based one.

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 a concrete decision context by framing the question it answers ('are there any scheduled monuments on or near this land') and naming two use cases (development checks, metal-detecting permission). It stops short of excluding alternatives or telling the agent when to prefer scheduled_monument_search or listed_building_search instead.

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