Western Astrology MCP Server by RoxyAPI

Solar arc directions calculator - directed chart at one degree per year

post_astrology_solar_arc

Read-only

Calculate a solar arc directed chart for any birth moment and target date. The solar arc is the secondary-progressed Sun longitude minus the natal Sun longitude, about one degree for each year of life, and every natal point including the Ascendant and Midheaven is advanced forward by that same arc. Returns the solar arc, each directed point with its natal and directed longitude, zodiac sign, degree, and a plain language interpretation, for predictive astrology apps timing major life events. Built on accurate tropical chart positions, no astronomy expertise needed.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`date`	Yes	Birth date in YYYY-MM-DD format. Determines planetary positions for the specific calendar day.
`lang`	No	Response language (BCP 47). Supported: en, tr, de, es, hi, pt, fr, ru, zh-Hans, zh-Hant. Defaults to en. Coverage varies by domain, and a field with no translation in the requested language returns English.	en
`time`	Yes	Birth time in 24-hour HH:MM:SS format. Determines the Ascendant (rising sign) and house cusps. Use 12:00:00 if unknown.
`compact`	No	Set true for the same data in a compact shape: arrays of same-shaped objects arrive columnar as {"__cols":[names],"__rows":[[values]]}. Lossless, typically 40 to 52 percent fewer tokens.
`latitude`	Yes	Birth location latitude in decimal degrees (-90 to 90). Positive = North, negative = South.
`nodeType`	No	Lunar node convention. "mean" is the smoothed average node, which always moves retrograde; "true" is the osculating node, which tracks the real perturbed node, oscillates up to about 1.5 degrees either side of the mean on a 173-day cycle, and can briefly turn direct. Neither is more correct and they almost always fall in the same sign. Applies to the North and South Node. True is the osculating node and the default, because it is what most Western chart software reports; mean is the smoothed node preferred by several evolutionary schools, so pass "mean" to match one. Nothing else in the chart changes, and the two agree on the sign except when the node sits within about 1.8 degrees of a cusp. Defaults to "true".	true
`timezone`	Yes	Timezone: IANA name (e.g. "America/New_York", "Europe/London") OR decimal hours from UTC (e.g. -5 for EST, 1 for CET). IANA strings are resolved to the DST-correct offset for the given date, so you can pass `cities[0].timezone` from /location/search directly.
`longitude`	Yes	Birth location longitude in decimal degrees (-180 to 180). Positive = East, negative = West.
`targetDate`	Yes	Date to direct the chart to, in YYYY-MM-DD format. Every natal point is advanced by the solar arc accumulated from birth to this date, about one degree for each year of life.

TDQS

A3.6/5.0

Behavior3/5

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

The annotations (readOnlyHint=true, destructiveHint=false) already declare that this is a safe, non-mutating operation, and there is no contradiction. The description adds 'Built on accurate tropical chart positions' and a plain-language interpretation, which is context but not disclosure of meaningful behavioral traits such as edge cases around missing times or the fidelity of the interpretation layer. Since the safety profile is implied, the extra value is moderate — a solid 3.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, well-structured paragraph with a reasonable length for a 9-parameter, output-rich tool. The key concept (solar arc arithmetic) is front-loaded, followed by return contents and use case. The closing phrase 'no astronomy expertise needed' is marginal filler, but the rest of each sentence carries information, so it remains efficient overall.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

This tool has no output schema, so the description does the entire job of explaining return values; it enumerates the solar arc, each directed point's natal/derived longitudes, sign, degree, and interpretation — adequate for an agent to understand the result shape. Combined with 100% schema-backed parameters and read-only annotations, the definition is functionally complete. The prior mention of explicit sibling disambiguation is the only notable omission within a complete tool description.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

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 prose, however, adds conceptual semantics that reinforce parameter meaning: the solar arc is defined as secondary-progressed Sun minus natal Sun, and the effect on targetDate ('every natal point... advanced by that same arc') is clearly expressed. This enrichment helps an agent understand how targetDate, date, and the returned positions relate, pushing the score to 4.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

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: 'Calculate a solar arc directed chart for any birth moment and target date.' It then explains the technique (forwarding all natal points by the solar arc of ~1 degree per year), which leaves no ambiguity about what the tool produces. It does not explicitly name a sibling tool it is not, so it stops short of a 5, but the distinctive mechanism makes it easy to distinguish from transits, progressions, and solar returns.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description gives a concrete use context: 'for predictive astrology apps timing major life events.' That tells an agent when solar arc is relevant, but it does not explicitly compare against alternatives, state when NOT to use this tool (e.g., when secondary progressions or transits would be more appropriate), or name a competing sibling like post_astrology_progressions. The guidance is implied rather than stated, warranting a 3.

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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TDQS

A3.8/5.0

Disambiguation3/5

Most tools are scoped to a clearly distinct domain—moon phases, houses, returns, fixed stars, astrocartography—but several pairs overlap, notably synastry vs. compatibility_score and transits vs. transit_aspects. The descriptions are long and do help an agent choose, but the boundaries are not always obvious at the name level.

Naming Consistency4/5

Every tool follows the same snake_case get_astrology_/post_astrology_ prefix pattern, making the group predictable and readable. However, collection endpoints like get_astrology_planet_meanings_id and get_astrology_signs_id awkwardly combine plural collection and singular id naming, and names like calendar_year_month depart from the cleaner resource+suffix pattern.

Tool Count2/5

With 38 tools, this is well over the 25+ threshold and feels heavy for an agent to traverse. While Western astrology is a broad domain, several near-duplicate endpoints, especially synastry/compatibility and transits/transit_aspects, could be consolidated into fewer, more scoped tools.

Completeness5/5

The toolset is comprehensive, covering natal charts, relationships, transits, returns, progressions, aspects, houses, relocation, and reference data. It includes enough specialized endpoints for both casual horoscope use and in-depth astrological analysis, with no obvious dead ends for the stated domain.

Resources

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