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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered without the description. The one genuine addition is the '[Cost: 10 credits (Tier 1)]' tag, which tells the agent about a metered call that no annotation conveys. Nothing is said about what the calculation covers, accuracy, or result shape.

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?

It is extremely short and front-loaded, with the subject in the first line and only the group/cost metadata after it; nothing is redundant or padded. The terseness reflects under-specification rather than bloat, so it scores well here while losing points elsewhere.

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 described, but the definition is still inadequate for a 15-parameter, 4-required tool: no indication of which inputs matter, no usage context, and no differentiation from the duplicate Hellenistic sibling. An agent would be guessing about how to invoke this correctly.

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 only 33% across 15 parameters, so the description carries a heavy compensation burden and adds nothing: no mention of the required date/time/latitude/longitude quadruple, the timezone-vs-timezoneOffset tradeoff, or the compact-mode fields/precision options. Undocumented parameters such as cosmogram, zodiacType, houseSystem and ayanamsaId receive no clarification from the prose.

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 specific subject ('Heliacal phases and stations') and locates it in a tradition group, so the agent can tell it is an observational-astronomy calculation rather than, say, a chart render. However, it is a bare noun fragment with no verb and no hint of what is computed or returned, and it does not distinguish itself from the near-identical sibling astroway_hels_stations_and_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?

There is no when-to-use guidance at all: no prerequisites, no statement of what inputs are needed to produce phases/stations, and no routing toward the many adjacent phase-related siblings (astroway_calendar_moon_phase, astroway_calendar_planetary_phases, astroway_hels_stations_and_phases). The group and cost tags are metadata, not usage guidance.

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