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

Annotations already declare the safe read-only, idempotent, open-world profile, so the description only needs to add context. It does add the geographic coverage and, usefully, the semantic that latestValue is expressed in the station's own unit, which is not derivable from the annotations or schema.

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?

A single sentence with the core purpose front-loaded and the scenario list and filters following it; the em-dash enumeration of station types is slightly heavy but each item disambiguates scope. No filler or repetition.

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, so return values need not be explained, and with the unit note and filter semantics included the definition is sufficient to call the tool correctly. The only omission is routing to siblings (get_station by ID, get_readings for measurements), which would help in this crowded tool set.

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% and both parameters are fully documented there, including the ISO 3166-2 example. The description's phrases 'by name or water body' and 'region (a German federal state or a country code)' restate the schema rather than adding new meaning, so the baseline 3 applies.

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 states a specific verb ('Search') and resource ('stations') and enriches the resource with its subtypes (river gauges, groundwater wells, reservoirs, coastal gauges) and geographic scope. The verb/name contrast with the single-station sibling get_station is implicit rather than stated, so sibling differentiation is not explicit.

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 tells the agent that the region filter is optional and what the two lookup modes are (by name or water body), which implies when to use each. But no alternative tool is named and there are no conditions for choosing search_stations over get_station or get_readings, 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.