sky_nowToday's sky (or any date from 1901 to 2100): the Moon's phase, sign and how much is lit, the next full moon (with its traditional name) and new moon, which planets are retrograde and until when (answers "is Mercury retrograde?"), and the sign of every planet.
| Name | Required | Description | Default |
|---|---|---|---|
| date | No | Optional date, YYYY-MM-DD (noon UTC). Default: right now. |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare this as a safe, read-only, idempotent, non-destructive operation, so the description does not need to carry the safety burden. It adds useful behavioral context beyond annotations by specifying the supported date range and enumerating the astronomical data returned, including traditional full moon names and retrograde end dates.
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 a single front-loaded sentence that immediately states the scope and then enumerates the useful outputs. It is dense but efficient, with the parenthetical 'answers is Mercury retrograde?' earning its place by grounding the tool in a common query.
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?
Given only one optional parameter and no output schema, the description is complete enough for correct invocation: it covers the default date, supported date range, and all major returned data categories. Nothing essential for selecting or calling the tool 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%, so the schema already documents the optional date format, noon UTC handling, and default. The description adds meaningful constraint beyond the schema by stating the allowed range of 1901 to 2100, which helps an agent know when the parameter is valid.
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 clearly states the resource and contents: today's sky or any date from 1901 to 2100, including Moon phase, lunar dates, retrogrades, and planetary signs. It implicitly distinguishes itself from birth_chart and famous_chart by focusing on current/sky data rather than natal charts, though it does not name the siblings 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?
Usage context is clear: use it for today's sky or historical/future dates in the 1901–2100 range, including common questions like 'is Mercury retrograde?'. It does not explicitly state when to prefer sibling tools such as birth_chart, but the context is sufficiently clear for an agent.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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