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

Annotations cover the safety profile (readOnly, idempotent, openWorld), so the description correctly focuses on behavior beyond that: the upstream data sources (PVGIS, federal price study 2025, Pronovo EIV 2026), the CH-vs-DE asymmetry in what is returned, and the instruction to cite sources and label it a rough estimate. It does not cover error/edge behavior, which keeps it just short of a 5.

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?

One dense, front-loaded sentence carries the core purpose and scope, followed by the exclusions and the alternative. Every clause earns its place, though the single sentence is long enough that structure is slightly strained.

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 fills the gap by naming the returned values and pointing to fullReport.url for the omitted metrics. Combined with the source-citation instruction, an agent has everything needed to call and report the result correctly.

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 all seven parameters already carry units, ranges, defaults and examples (e.g. azimuth conventions, tilt for flat roofs). The description adds only the implicit address/country context and nothing about parameter syntax, so the baseline 3 is appropriate.

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 ('First estimate for a rooftop solar system') with explicit geographic scope (Swiss or German address) and enumerates what the estimate contains (annual yield, turnkey cost, subsidy, feed-in tariff). Clearly distinguishable from the unrelated siblings geocode_address and list_cities.

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?

Explicitly states when to use it and, critically, what it does NOT cover (measured shading, self-consumption, savings, payback), naming the alternative path (fullReport.url / the Soljo report) for those needs. This is exactly the when/when-not/alternative structure.

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