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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered structurally. The description adds one genuinely useful behavioral fact not in the annotations — the 20-credit (Tier 2) cost — but says nothing about rate limits, whether results depend on the observer's location, or how the phase set is computed. With annotations carrying the safety burden, this is adequate but thin.

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?

A single front-loaded sentence that names the operation, the scope ('each planet relative to the Sun'), and the full phase vocabulary, followed by compact group/cost metadata. Nothing is wasted, though the enumerated phase list could be trimmed since the output schema presumably carries the values.

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?

An output schema exists, so return values need not be explained, and annotations cover safety. However, for a 15-parameter tool with only 33% schema coverage, the description omits why latitude/longitude are required for a planetary-phase calculation and how ayanamsa/zodiacType affect the result. Minimum viable, with clear gaps.

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 description mentions no parameters at all, and schema description coverage is only 33% across 15 parameters. Several undocumented parameters (cosmogram, zodiacType, houseSystem) plausibly alter the computed phases, yet the description does not explain any of them. With coverage below 50%, the description was expected to compensate and does not.

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: 'Calculate the synodic phase of each planet relative to the Sun,' and enumerates the eight phase names so the agent knows exactly what output to expect. It is distinguishable from astroway_calendar_moon_phase by the phrase 'each planet,' but the description never names that sibling or otherwise explicitly differentiates itself from the surrounding calendar tools.

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 guidance, no exclusions, and no named alternative. The only routing signal is the bracketed '[Group: Calendar & Cycles]' label, which is category metadata rather than usage guidance. An agent must infer from the tool name alone when this beats astroway_calendar_moon_phase or astroway_calendar_planetary_cycles.

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