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

With no annotations, the description adds useful behavioral context by noting it 'Handles midnight sun and polar night' and includes a 'day-over-day trend.' It does not explicitly state read-only behavior, but the 'get' verb and 'pure sun times' scope imply a safe calculation tool.

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, front-loaded with output details, no fluff. Every clause adds value, from the comprehensive list of times to the edge-case handling and usage pointer.

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 tool with 4 parameters and no output schema, the description fully covers what the tool returns, edge cases, and when to use it. The timezone parameter is well-covered in the schema, so no gap remains.

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 parameters are already well-documented. The description mentions 'location and date' but adds no extra meaning beyond the schema's parameter descriptions, meriting the baseline score.

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 lists specific outputs (sunrise, sunset, solar noon, civil dawn/dusk, golden hour, day length) and explicitly contrasts with vitamin D tools, making the tool's purpose unmistakable and differentiated from siblings.

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 clearly states when to use this tool vs. alternatives: 'Pure sun times — for vitamin D questions use the vitamin_d tools instead.' This provides an explicit exclusion and points to the correct sibling tools.

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