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Open Ephemeris

Open Ephemeris

by openephemeris
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Remote

House Cusps

ephemeris_house_cusps
Read-onlyIdempotent

Calculates the twelve house cusps and ASC/MC/DSC/IC for a given date, time, and place, supporting multiple house systems for astrology chart analysis.

Instructions

Use this when the user asks 'what are my house cusps', 'which sign is my 7th house', 'what's my Midheaven', 'show my houses in Whole Sign' or 'compare Placidus and Koch' — houses and angles only, for a date, time and place. Returns the twelve cusps and ASC/MC/DSC/IC for each requested system.

HOUSE SYSTEM CODES: P=Placidus, K=Koch, O=Porphyry, R=Regiomontanus, C=Campanus, E=Equal, W=Whole Sign.

CREDIT COST: 1 credit per call.

Input Schema

NameRequiredDescriptionDefault
datetimeYesISO 8601; zone required (`Z`/offset, or local time plus `timezone`).
latitudeYesObserver latitude.
timezoneNoIANA zone for a local datetime.
longitudeYesObserver longitude.
house_systemsNoCodes, e.g. ['P','W']. Default ['P'].

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed5 schema fields changedv4.29.0
    • changedInput schema / properties / datetime / description
      Previous value: -"ISO 8601 datetime. A datetime with no zone is rejected; give a `Z` or ±HH:MM suffix, or a local time with the `timezone` argument. Date-only resolves to 12:00 UTC."New value: +"ISO 8601; zone required (`Z`/offset, or local time plus `timezone`)."
    • changedInput schema / properties / house_systems / description
      Previous value: -"List of house system codes. E.g. ['P', 'W']. Defaults to ['P'] (Placidus)."New value: +"Codes, e.g. ['P','W']. Default ['P']."
    • changedInput schema / properties / latitude / description
      Previous value: -"Observer latitude in decimal degrees."New value: +"Observer latitude."
    • changedInput schema / properties / longitude / description
      Previous value: -"Observer longitude in decimal degrees."New value: +"Observer longitude."
    • changedInput schema / properties / timezone / description
      Previous value: -"IANA timezone (e.g. `America/Chicago`); required when the datetime is naive, ignored otherwise."New value: +"IANA zone for a local datetime."
  2. Changed2 schema fields changedv4.24.2
    • changedInput schema / properties / datetime / description
      Previous value: -"ISO 8601 datetime; zone required — a `Z`/±HH:MM suffix or the `timezone` argument. Date-only resolves to 12:00 UTC. Full rule: server `instructions`."New value: +"ISO 8601 datetime. A datetime with no zone is rejected; give a `Z` or ±HH:MM suffix, or a local time with the `timezone` argument. Date-only resolves to 12:00 UTC."
    • changedInput schema / properties / latitude / description
      Previous value: -"Observer latitude in decimal degrees. Resolve from a place name with location_search; never recall coordinates from memory."New value: +"Observer latitude in decimal degrees."
  3. Changed3 schema fields changedv4.8.0
    • changedInput schema / properties / datetime / description
      Previous value: -"ISO 8601 date/time in UTC or with offset (e.g. '2026-03-20T12:00:00Z')."New value: +"ISO 8601 datetime; zone required — a `Z`/±HH:MM suffix or the `timezone` argument. Date-only resolves to 12:00 UTC. Full rule: server `instructions`."
    • changedInput schema / properties / latitude / description
      Previous value: -"Observer latitude in decimal degrees."New value: +"Observer latitude in decimal degrees. Resolve from a place name with location_search; never recall coordinates from memory."
    • addedInput schema / properties / timezone
      Added value: +{
+  "description": "IANA timezone (e.g. `America/Chicago`); required when the datetime is naive, ignored otherwise.",
+  "type": "string"
+}
  4. First observedv0.1.0

TDQS

A4.4/5.0
Behavior4/5

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

Annotations already declare readOnly/idempotent/openWorld=false, so the safety profile is covered; the description adds genuinely new behavioral facts — the exact output set per system and the 1-credit cost per call. It does not describe error behavior for invalid or missing timezone data, which is the main remaining gap.

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?

Front-loaded with when-to-use and example queries, then the code table, then cost — a sensible ordering where every block earns its place. The example-query list is slightly longer than strictly necessary, but it is the highest-value content for tool selection.

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

Completeness5/5

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

For a read-only, stateless calculation with no output schema, the description supplies everything needed: trigger cases, scope boundary, output shape, the enum values for the one non-obvious parameter, and the credit cost. Nothing an agent needs to call it correctly is missing.

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 coverage is 100%, so the baseline is 3, but the description adds real value the schema lacks: the full enumeration P/K/O/R/C/E/W with meanings, whereas the schema only says 'Codes, e.g. ["P","W"].' That mapping is what makes the house_systems parameter usable without guessing.

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

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb+resource — compute house cusps and angles for a datetime/place — and explicitly bounds scope to 'houses and angles only, for a date, time and place.' It also states the return contents (twelve cusps plus ASC/MC/DSC/IC), which separates it from angle-only siblings like ephemeris_angles_points and full-chart tools like ephemeris_natal_chart.

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

Usage Guidelines4/5

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

Four concrete user phrasings ('what are my house cusps', 'which sign is my 7th house', 'show my houses in Whole Sign', 'compare Placidus and Koch') give an agent a clear trigger signal, and 'houses and angles only' scopes out non-house requests. It stops short of naming the sibling to use instead when the user wants a full chart, so the exclusion is implicit rather than routed.

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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