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

Annotations already declare the safe read-only, idempotent profile, so the bar is lower. The description adds genuinely useful operational limits not present in structured data: minimum step of 0.01 days and the range caps (1 year for sub-day steps, 5 years otherwise). The stated cost tier further informs budget-conscious callers.

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?

Two tight, front-loaded sentences that lead with purpose before the operational constraints, with no filler. The group/cost tags are compact metadata rather than prose padding.

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, and the key behavioral constraints are covered. But routing ambiguity against the many sibling ephemeris/chart tools and the undocumented date format leave gaps for correct invocation.

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 only 33%, so the description is expected to compensate. It adds meaning for stepDays ('configurable step, min 0.01 days') and planetIds ('optionally filter by planetIds'), but stays silent on the date format and stepDays' default/units, leaving the sparse schema to carry the rest.

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 ('Return planet positions for a date range') with the configurable step, which is clearly distinguishable from a single-moment tool. However, it never contrasts itself with close siblings like astroway_western_planets or the calendar ephemeris tools, leaving the agent to infer which one applies.

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 provides constraints (max range, optional planetIds filter) but no explicit when-to-use guidance or named alternatives. An agent cannot tell from this text when to reach for the ephemeris range versus astroway_western_planets 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.