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

Annotations already declare readOnly, idempotent, non-destructive, so the safety profile is covered. The description adds genuinely new behavioral context: the temporal coverage ('usually yesterday'), the presence of quality flags, and the exact data fields returned, which is valuable since there is no output 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?

Two tightly packed sentences: purpose and fields first, then the prerequisite pointer. Front-loaded and free of filler, though the field enumeration makes it slightly dense.

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 single-parameter, read-only lookup with full schema coverage and annotations, the description supplies purpose, return content, and param provenance, which is nearly everything needed. Only an explicit contrast with dwd_daily 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 coverage is 100%, so the single parameter is already documented as 'DWD station number.' The description goes beyond that by telling the agent where to source the value ('Get station_id from dwd_stations'), adding provenance meaning the schema lacks.

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: 'Most recent daily climate observation for one German DWD station,' then enumerates the returned fields (temperature, precipitation, sunshine, snow, wind, humidity). This lets an agent distinguish it from historical tools like dwd_daily, though it never names that sibling explicitly.

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 'most recent ... usually yesterday' framing implies when to reach for it, and 'Get station_id from dwd_stations' gives a concrete prerequisite-routing hint. However, it never states when NOT to use it or how it differs from dwd_daily, so the agent must infer the boundary.

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