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

Annotations already declare the read-only, idempotent, non-destructive profile, so the safety burden is lifted. The description adds real behavioral context beyond that: the 92-day maximum range, UTC interpretation, and the exact astrological rule governing inclusions. It does not describe output shape, but an output schema exists to cover that.

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?

Front-loaded with the core purpose, then cleanly sectioned into workflow, input contract, and disambiguation. Every block earns its place, though the trailing external docs link is a mild dependency and the Lilly citation is slightly ornamental.

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?

Given annotations covering safety, a full output schema, and a 100%-covered input schema, the description supplies everything else an agent needs: what the tool computes, the rule behind it, range limits, and sibling disambiguation. Nothing required for correct invocation is missing.

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 baseline is 3. The description adds value beyond the schema by disclosing the 92-day upper bound on to_date and its inclusive semantics, constraints the schema does not state. It does not explain response_format, but that parameter is self-describing with an enum.

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 verb and resource ('Lists void-of-course Moon periods in a date range') and immediately defines the term with the precise traditional rule, so an agent knows exactly what constitutes a void period. It also names the sibling tools it is not (moon phase, transits), removing ambiguity in a crowded namespace.

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?

Provides an explicit WORKFLOW block (standalone BEFORE; chain into get_western_planetary_hours to pick an hour inside a non-void window) and a DO NOT CONFUSE WITH section naming two siblings and why each differs. This is exactly the routing information an agent needs.

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