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

Beyond the readOnly/idempotent/non-destructive annotations, the description discloses what the annotations cannot: the per-region data sources (swissALTI3D 2 m, Copernicus GLO-30 30 m, GEBCO at sea), the crucial difference that GLO-30 measures surface including buildings and trees while swissALTI3D measures ground, a legally required attribution ("© swisstopo"), and the billing model where one point equals one lookup.

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 sentences, front-loaded with the definition and output unit, then the source/accuracy caveats, then the cost model. Every sentence carries distinct information, including the attribution obligation, with no filler.

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?

For a geospatial lookup with no output schema and only two parameters, the description covers the important unknowns: units, sign, vertical datum caveats by source, and quota behavior. It leaves secondary details (whether results preserve input order, how out-of-coverage or sea-adjacent points are reported) unstated, which keeps it from a 5.

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 100%, so lat/lon bounds and max_chars are already documented; the baseline would be 3. The description earns an extra point by explaining that each element of `points` is charged as a lookup and that account_status reveals the per-call plan maximum, which is quota semantics the schema cannot express.

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?

"Heights above sea level in metres for a list of points" names a specific resource and output unit, and "negative at sea" pins down the sign convention. It implies the contrast with elevation_profile (a list of discrete points rather than a sampled line) but never names that sibling explicitly, so an agent must infer the boundary.

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?

The qualifying clause "for a list of points" hints at when this is the right tool over elevation_profile, and the lookup/plan-maximum note signals a cost constraint per call. There is no explicit when-to-use or when-not-to-use statement and no named alternative, so guidance stays implied.

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