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

Annotations already establish readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds value beyond that by revealing the returned domain fields and implying the result can be plural (several municipalities), which is behavioral context the annotations do not convey. It stops short of describing error behavior for out-of-range or unknown postcodes.

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 sentences: the first front-loads what is looked up and returned, the second states the usage trigger. No filler, no redundancy with the title.

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?

With no output schema, the description carries the burden of explaining returns and does so by naming the three returned data categories. For a one-parameter, read-only lookup that is close to complete; only the shape of the response (single object vs list of municipality records) is left implicit.

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%: the single parameter is documented as 'Swiss 4 digit postcode' with min/max bounds. The description adds no format, padding, or edge-case detail (e.g. leading zeros, validity of 1000/9999) beyond the schema, 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?

States a specific verb ('look up') and resource ('Swiss postcode') and enumerates what comes back: municipalities, canton, BAG premium region. That is far more informative than the title. It does not, however, explicitly distinguish itself from the sibling tools (compare_insurance, draft_switch_letter, switching_deadlines), relying on the reader to infer it is a data-lookup rather than an insurance workflow tool.

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?

Gives a concrete triggering condition: 'Use it when a postcode may cover several municipalities,' which tells the agent when this lookup is warranted. It does not name an alternative tool or state when not to use it, but with unrelated siblings there is little to exclude.

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