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

Annotations already cover readOnly, idempotent, openWorld and non-destructive, yet the description still adds substantive behavior: the site is geocoded through OpenStreetMap, results assume flat ground with no neighbouring buildings, and the output is explicitly not a legal shadow certificate. The only meaningful gap is error behavior when the site cannot be resolved.

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?

Four sentences, each carrying distinct information: outputs, usage, data source, and limitations. It is front-loaded with what the tool returns. Slightly dense but no filler sentences.

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 describing the return values, and it does so explicitly (azimuth, elevation, shadow length per metre, shadow direction, sunrise/sunset). Combined with the flat-ground caveat and the OSM lookup disclosure, an agent has what it needs; only failure/edge-case behavior is unaddressed.

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 baseline is 3. The description still adds value the schema does not: times are local Central European time, which resolves real timezone ambiguity, and it clarifies that building_height_m converts per-metre shadow figures into absolute lengths. That is genuine semantic addition on top of a well-documented schema.

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 concrete outputs (sun azimuth and elevation, shadow length per metre of building height, shadow direction, sunrise/sunset) for a specific resource: a building site on a given day. That is far beyond a restatement of the title. It does not, however, differentiate itself from a plausibly overlapping sibling such as vedutum_add_solar, so it stops short of a 5.

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 states positive usage contexts ('orientation, terrace or window planning and quick shadow questions') and a clear exclusion ('A study on flat ground without neighbouring buildings, not a legal shadow certificate'), which sets expectations about accuracy and scope. No sibling alternative is named, so it is clear context without explicit routing.

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