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

Annotations only declare readOnlyHint and openWorldHint, so the description carries the burden of disclosing the async lifecycle — the possibility of a 'computing' status and the retry_after_s field — which is genuinely non-obvious behavior an agent must handle. It also discloses that results come with uncertainty and method metadata. It stops short of covering latency expectations, failure modes for unknown addresses, or rate limits.

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 tight sentences: the first front-loads what is returned and for what input, the second front-loads the async retry caveat. No filler, no repetition of the title or annotations.

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 does the work of naming the returned fields (yearly and solstice sun hours, uncertainty, method, link) and the status/retry_after_s control fields, which is enough to call and interpret the tool. The remaining gap is the missing distinction from sun_hours_at, which matters given a near-identical sibling.

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%, with both address and lang fully documented including an example address and the default language, so the baseline of 3 applies. The description adds only a light restatement that the address must be Norwegian, without clarifying the lang parameter's effect on output beyond what the schema already says.

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 resource (hours of direct sun per year plus winter/summer solstice values) and a precise scope (a Norwegian street address), along with the bundled outputs (uncertainty, method, link). It does not differentiate itself from the sibling sun_hours_at, so an agent cannot tell from the description alone which of the two to pick.

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?

Usage context is implied by the 'Norwegian street address' constraint, and there is a useful operational instruction to re-call after retry_after_s when status is 'computing'. However, there is no explicit guidance on when to prefer this tool over sun_hours_at, nor any stated prerequisites or exclusions.

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