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

Annotations already declare readOnlyHint=true, destructiveHint=false, idempotentHint=true, and openWorldHint=true, covering safety and idempotency. The description adds minimal new behavioral context (e.g., data source 'US Naval Observatory'), but does not disclose additional traits like rate limits or authentication. With annotations providing strong coverage, the description's incremental value is limited, earning a 3.

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 description is two sentences with zero wasted words. The first sentence front-loads the primary purpose (equinox/solstice dates and times), and the second efficiently adds perihelion/aphelion and the authoritative source. Every sentence provides essential information.

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?

The tool is simple (one optional parameter, output schema exists). The description covers all returned events, the source, and the applicable year range (implicitly via schema). Given the presence of an output schema, the description is fully complete for an agent to understand what the tool offers and when to use it.

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?

The input schema has 100% coverage for the single parameter 'year', including a description and constraints. The tool description merely restates 'for any year' without adding new semantics or usage nuance. Baseline 3 is appropriate as the schema already fully documents the parameter.

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 clearly states the tool provides exact dates and UTC times for specific astronomical events: vernal equinox, summer solstice, autumnal equinox, winter solstice, plus perihelion and aphelion. The verb 'Get' and resource list make the purpose unambiguous, and the specific events differentiate it from sibling tools like moon phases.

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?

The description explicitly says 'for any year', indicating the primary usage context. It does not directly compare to sibling tools (e.g., usno.astronomy.moon_phases), but the specificity of events implicitly guides selection. A brief note on when not to use it (e.g., for moon phases) would improve clarity, but current clarity is sufficient for an agent.

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