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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely useful context beyond them: the endpoint, the four required inputs, and a 20-credit Tier 2 cost, which is a real operational constraint an agent should weigh before calling.

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 front-loaded and dense with useful detail, and the bracketed metadata block is scannable. The trailing metadata lines are somewhat boilerplate but cheap and informative.

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 15-parameter tool the description is thin: it omits the sidereal/tropical and ayanamsa choices that materially change results, and does not clarify the relationship to sibling phase/cycle tools. An output schema exists, so return values need not be explained, which keeps this at an adequate rather than poor level.

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?

With 15 parameters and only 33% schema description coverage, the description carries real burden, yet it merely restates the four required fields already listed in the schema's required array. Eleven optional parameters (zodiacType, houseSystem, cosmogram, city, name, ayanamsaId, etc.) go unmentioned, and nothing explains why latitude/longitude matter for a phase calculation.

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 (calculate) and resource (synodic phase of each planet relative to the Sun), and enumerates the eight phase names, so an agent knows exactly what is produced. It does not explicitly distinguish itself from close siblings like astroway_calendar_moon_phase or astroway_calendar_planetary_cycles, leaving the planetary-vs-lunar distinction to inference.

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 never says when to choose this tool over alternatives, nor does it exclude cases (e.g. single-planet phase vs moon phase). The bracketed metadata gives required inputs and a cost tier, which is operational context rather than usage guidance.

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