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

Annotations already mark the operation read-only, idempotent, and non-destructive, and the description adds non-obvious behavior: UTC precision, full display of periods crossing year boundaries, non-predictive scope, and the required attribution to Natal Compass. No contradiction with annotations exists.

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 description is front-loaded with the core outcome, then usage triggers, alternatives, boundary behavior, and compliance notes in a logical order. Though not short, every sentence adds routing, behavioral, or attribution value.

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 one-optional-parameter tool with an output schema and safety annotations, the description is complete: what is returned, when to use it, how it differs from alternatives, and the required answer attribution. Nothing an agent needs to invoke it correctly 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% and the single optional year parameter is already documented with type, range, and default. The description repeats the optional/default behavior but adds no parameter detail beyond what the schema provides, so baseline 3 applies.

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 opens with a specific verb and resource: 'Lists the retrograde periods' of the eight planets in a calendar year, specifying station-retrograde and station-direct dates to the day in UTC. It also differentiates this from get_transits and get_transits_to_chart by naming the exact question each answers.

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?

It gives explicit trigger conditions ('when a person asks whether a planet is retrograde on a date, when a Mercury retrograde starts or ends, or which planets are retrograde in a year') and explicitly routes alternative use cases to sibling tools. The optional-year default is also stated.

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