Mercury retrograde

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

Annotations already declare readOnly, idempotent, non-destructive and openWorld=false, so safety is covered. The description adds genuine context beyond that: temporal precision ('to about a minute'), UTC plus a chosen time zone, and the fact that station degrees and signs are included in the output.

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 with no filler; the parentheticals carry real information (default range, precision, time zone, station data) rather than padding. Slightly dense, but every clause earns its place.

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?

With no output schema, the description carries the burden of describing returns, and it does so by naming the four time points plus degree/sign data and the time zone handling. Combined with the fully documented schema, an agent has everything needed to call and interpret this tool.

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%, so all three parameters are already documented with defaults, patterns, and the 30-year cap. The description only restates the default range behavior, adding little beyond what the schema provides. 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?

States a specific resource (Mercury retrograde periods) and a precise scope (overlapping a date range), then enumerates the exact artifacts returned: pre-shadow start, both stations, and post-shadow end. This is clearly distinguishable from siblings like moon_phase or transits.

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?

Usage is implied by the astronomy domain and the defaults ('default: the next 12 months'), but there is no explicit when-to-use guidance or routing against siblings such as transits or moon_phase. An agent can infer intent but receives no conditional steering.

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