Retrograde Station Tracker

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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so safety is covered. The description adds genuinely useful behavior the annotations don't carry: the default window (next 90 days), the hard cap of one year, and a per-call credit cost of 5 — cost disclosure is rare and valuable for agent planning.

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 blocks: trigger examples plus payload/scoping in the first, cost in the second. Every sentence earns its place and the highest-value routing information (the user phrasings) is front-loaded.

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 read-only, no-output-schema tool with four optional params, the description covers the return fields, defaults, range cap and cost — enough to call it correctly. The remaining gap is the unexplained 'format' enum and no statement of what timezone the returned times use.

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 100%, so the baseline is 3. The description restates the date-range default in prose and clarifies the planet span (Mercury through Pluto) versus the schema's default of Mercury–Saturn, but it does not explain the 'format' enum (json vs llm) or confirm the timezone basis for returned times.

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: it returns every retrograde and direct station from Mercury through Pluto, with time, longitude and sign. The verbatim user-question examples ('when does Mercury go retrograde', 'Mercury retrograde dates for 2026') make the scope (station dates in a range) clear against a sibling like ephemeris_retrograde_status, though no sibling is named explicitly.

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?

Gives concrete trigger conditions through quoted user phrasings, which is stronger than generic 'use for retrograde questions'. It does not say when NOT to use it or name an alternative tool (e.g. current-status vs historical stations), which keeps it short of a 5.

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