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

Annotations already cover readOnly, idempotent, non-destructive and closed-world, so the description is free to add what they can't: ground vs. surface modelling (Copernicus includes buildings and trees), 2 m vs. 30 m resolutions, negatives at sea, and an attribution obligation ('credit © swisstopo'). Only the return shape and behaviour for unsupported points are left unstated.

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-loaded with the core output (metres above sea level, negative at sea), followed by coverage, then billing. The telegraphic source list is dense but every clause carries information; nothing is padded.

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 two-parameter read-only lookup this covers accuracy expectations, geographic coverage, licensing and cost. With no output schema, the one remaining gap is that it never states the response is a per-point list of heights in input order.

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 bounds and max_chars truncation-with-offset behaviour are already documented in the schema. The description adds only that each point is billed as one lookup, a useful cost semantic but a marginal addition.

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?

The description names a concrete verb-and-resource ('Heights above sea level in metres for a list of points') and backs it with data sources, so the purpose is unmistakable. It stops short of naming the sibling elevation_profile or explaining how the two differ, which is the main thing an agent must decide between.

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 gives indirect routing guidance by disclosing per-region sources (Switzerland/Liechtenstein vs. elsewhere on land vs. sea) and a cost model ('Each point counts as one lookup; account_status shows the plan maximum per call'), which implies when to batch or split calls. There is no explicit when-to-use/when-not statement and no comparison with elevation_profile or geocode.

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