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 genuinely useful behavior beyond that: times are emitted in a local time zone auto-detected from the coordinates. It still says nothing about accuracy caveats, polar day/night edge cases, or date-range limits, which for an astronomical calculator would be worth stating.

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?

The core sentence is dense and front-loads the returned data well, but the opening two fragments ('Sunrise, sunset, twilight and golden hour.' and 'Sun times.') are redundant restatements of the title and consume the most prominent position without adding information. Trimming them would sharpen the entry point.

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 correctly carries the burden of enumerating return values, and it does so thoroughly (all sun events, twilight bands, golden hour, moon data). It is slightly thin on output formatting (e.g. how day length is expressed) and edge-case behavior, but an agent has enough to call and interpret the tool.

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 four parameters (lat, lon, tz, date) are already documented with examples and defaults in the schema. The description's time-zone statement merely restates the schema's tz 'auto' semantics and adds no format, range, or edge-case detail beyond it, so baseline 3 applies.

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 concrete resource and enumerates exactly what is computed: sunrise, sunset, solar noon, day length, three twilight bands, golden hour, plus moon phase/illumination/rise/set. That is far more specific than the title alone. It does not, however, distinguish itself from the sibling 'moon_phase' tool even though it duplicates that capability, so sibling differentiation is incomplete.

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 is implied by the stated inputs ('for any coordinates and date'), which tells an agent this is the coordinate-based sun/moon calculator. There is no explicit when-to-use versus alternatives, and no mention of the overlapping 'moon_phase' or 'timezone_by_coordinates' siblings, nor any prerequisite (e.g. valid coordinates, date range limits).

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