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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=true, so the safety profile is covered. The description adds a genuine, non-schema fact — the operation costs 1 credit — plus the algorithmic approach, which sets expectations about precision. It does not describe result granularity or unit conventions, so it adds modest rather than rich context.

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?

It is a single sentence, which is appropriately sized and front-loaded with the core capability. However, the redundant 'Daylight Duration Calculator: Daylight Duration Calculator' prefix wastes the most valuable position in the text by restating the name twice.

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 simple three-parameter read-only calculator with an output schema present, the definition covers purpose, method, and cost — enough for an agent to call it correctly without further inference. The only meaningful gap is disambiguation from the SunriseSunset 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 format hints, defaults, and examples for all three parameters, so the schema carries the burden. The description only reiterates 'any geographic location and date' without adding coordinate conventions (e.g., decimal degrees, negative for west) or timezone semantics for the returned times.

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 a specific verb and outputs: computes sunrise, sunset times, and total daylight hours for a given location and date, plus the method (astronomical algorithms). That is far more than the title restated. It stops short of a 5 because it never distinguishes itself from close siblings such as SunriseSunset or SunPosition, which an agent could easily confuse it with.

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?

There is no when-to-use or when-not-to-use guidance, and no mention of the obvious alternatives (SunriseSunset, SunPosition, MoonriseMoonset) that overlap in function. The only usage signal is the implicit 'requires a location and date', which the schema already conveys.

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