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

Annotations already cover safety (readOnly, idempotent, non-destructive), and the description adds substantial context beyond them: source mixing (buildings/vegetation in Copernicus, EGM2008 heights vs. provider-declared datum), explicit failure behavior ('never zero elevation or low risk'), and stated unverified characteristics (deployment/version, local accuracy, licence, datum). It also warns that non-UK address lookup requires a configured geocoder, which the agent could not infer otherwise.

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?

Labelled sections (Purpose/When to use/Returns/Limitations/Parameter guidance/Chaining) make it scannable and front-loaded with the core purpose. It is dense and long for a single-value lookup, and some limitation clauses overlap (provider/datum caveats appear twice), but nearly every sentence carries decision-relevant information.

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, yet the description still usefully names the datum caveats and error semantics that matter for interpreting results. For a one-point lookup with nested site_ref chaining, nothing an agent needs to call it correctly is missing.

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 only 25%, so the description must compensate, and it does: it explains the three input routes (address, resolved site_ref, or coordinates with explicit country_code), states that country_code is mandatory for coordinate input, and flags the geocoder prerequisite for non-UK addresses. Minor gap: it never clarifies that all four params are optional or how conflicts between address and coordinates are resolved.

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 ('read one contextual elevation worldwide') plus the exact data sources (Copernicus GLO-30, or a configured Open Topo Data-compatible service). No sibling tool in the list computes elevation, so the scope is unambiguous and self-distinguishing.

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?

Explicit 'When to use: when a user asks about elevation at a known worldwide point', followed by an exclusion list ('One point does not establish slope, contours, drainage, flood risk, wind exposure, measured site levels or 3D terrain') that steers the agent away from misusing it for terrain analysis. Chaining guidance (pass site_ref unchanged) tells the agent how it fits into the wider workflow.

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