Caelus

Caelus is a clean‑room, MIT‑licensed TypeScript suite for validated astrology computation. It computes planetary positions, charts, events, hellenistic timing techniques, Vedic methods, and citable chart facts across browser, edge, Node, and MCP clients, without Swiss Ephemeris code, AGPL licensing, or ephemeris files. The project provides a rich API for developers to integrate precise astrological data into applications, with extensive documentation, a playground, and a growing set of MCP tools for AI clients.

Caelus is listed with 2 APIs on the APIs.io network. Tagged areas include Astrology, TypeScript, Open Source, MIT, and MCP.

The Caelus catalog on APIs.io includes 1 Spectral governance ruleset.

Caelus’ developer surface includes CLI, documentation, getting-started guide, API reference, changelog, and 11 more developer resources.

🌐 Visit website 📡 Profile data on GitHub

20.0/100 emerging Agent 16/100 agent aware Full breakdown ↓
scored 2026-11-13 · rubric v0.28.0 · Show this score on your site →

2 APIs 1 MCP Servers

Astrology TypeScript Open Source MIT MCP

Kin Score

Kin Score How this is scored →
scored 2026-11-13 · rubric v0.28.0

Composite quality — 20.0/100 · emerging

Contract Quality 2.0 / 21

Developer Ergonomics 7.3 / 17

Access Clarity 1.4 / 17

Operational Transparency 0.0 / 11

Contract Governance 2.2 / 10

Discoverability 4.8 / 9

Regulatory Posture 1.3 / 15

Agent readiness — 16/100 · agent aware

Machine-Readable Contract 18 / 18

Agentic Access Contract 0 / 10

Documented Reversibility 0 / 6

MCP Server 12 / 12

Machine-Readable Auth 0 / 10

Idempotency 0 / 9

Stable Error Semantics 0 / 8

Request/Response Examples 0 / 7

Rate-Limit Signaling 0 / 7

Typed Event Surface 0 / 6

Agent Skills 0 / 5

Well-Known Catalog 0 / 4

Consent & Bot Identity 0 / 3

A2A Agent Card 0 / 8

Dry-Run / Simulate Mode 0 / 4

Delegated User Identity 0 / 6

Protected Resource Metadata 0 / 5

Registration Without a Human 0 / 6

Agentic Commerce Well-Known Document 0 / 5

Pagination 5 / 5

Distinct Operations 3 / 3

MCP Tool Quality 6 / 6

Regulatory Posture applies to this provider. Its tags matched the Horizontal (data, software, accessibility, platform) regime, so Regulatory Posture carries 15 points of the composite. If this regime is wrong for your business, say so on your provider repo — the applicability map is public and we will correct it.

Create-or-Update Ergonomics could not be measured. We hold no machine-readable contract for this provider to read, so there is nothing to measure a write surface against. Excluded rather than scored zero: never-measured and measured-empty are different facts. Publishing an OpenAPI is what makes this facet — and several others — scorable at all.

The six quality facets above are damped to 85 points between them, because the conditional facet above carries the other 15. That is why each facet's contribution is shown against a damped maximum: raising a quality facet moves the composite by 85% of its nominal weight, not 100%. The full arithmetic is at apis.io/rating/.

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Agent readiness — checks not met, largest first (exact, from this profile):

Agentic Access Contract +10 pts — agentic_access artifact present (x-agentic-access), graded by author Ask about this →
Machine-Readable Auth +10 pts — a served openid-configuration/oauth-authorization-server carrying `issuer` (served), else the securitySchemes class in the provider OpenAPIs — bound (mutualTLS, DPoP, Signature) > negotiable (oauth2 authorizationCode/clientCredentials, openIdConnect) > bearer (http bearer, apiKey) Ask about this →
Idempotency +9 pts — OpenAPI mutating operations declare an idempotency key — a header, a request-body property, or a named de-duplication token whose own description says so (verified); else common[].type matches /idempoten/i (documented) Ask about this →
Stable Error Semantics +8 pts — OpenAPI $refs a shared error schema across 4xx/5xx responses (verified), else common[].type includes ErrorCatalog / ErrorCodes / DeclineCodes Ask about this →
A2A Agent Card +8 pts — a2a/-a2a.yml manifest, graded on conformance.grade against A2A 1.0.0 Ask about this →
Rate-Limit Signaling +7 pts — OpenAPI responses document X-RateLimit-* / RateLimit headers (verified), else a rate_limits artifact or RateLimits link (documented) Ask about this →

11 more unmet checks in the Agent Readiness table above.

Kin Score — facets with the most composite points still available (weight × headroom):

Contract Quality scores 9.4 — up to +22.7 composite points Ask about this →
Access Clarity scores 8.5 — up to +18.3 composite points Ask about this →
Operational Transparency scores 0.0 — up to +13.0 composite points Ask about this →

Each check links to what satisfies it. Publish the artifact, or tell us where it already lives, and the score moves on the next scoring run.

Not sure how this applies to your stack? Ask about any one item. Kin Lane reads every question, looks at your profile and your situation, and replies with what a fix would take — scoped to that one area, priced up front, yours whether you ship it or not. Ask a question →

Improve this rating by publishing the missing artifacts — every area above can be raised, and the full rubric is at apis.io/rating/. Every facet and dimension name above is a link: it opens that measurement's own page — what it means, the exact checks that feed it, how the whole catalog distributes on it, and the providers at the top of it. This rating is computed from the provider profile at artifacts.apis.io/ephemengine-com/apis.yml: open an issue on github.com/api-evangelist/ephemengine-com to ask a question or point us at an artifact you publish. Submit an artifact on GitHub — free → Manage your own listing — the Influence plan, $499/mo →

Standards implemented 1

Standards this provider implements or carries. De facto ones are profiled and measured by the API Commons; formal ones come from the standards directory and are linked by the provider's own tags. The evidence column says how each claim was established — not that it was made.

Model Context Protocol (MCP)

measured — observed by APIs.io (documented)

APIs 2

Individual APIs this provider publishes, each with its own machine-readable definition.

Caelus MCP

MCP streaming HTTP endpoint providing access to ephemeris data and tools.

Caelus API

Caelus API as documented publicly: 1 operations. Contract generated from the documentation by API Evangelist (2026-11-07); not the provider's own document.

MCP Servers 1

Model Context Protocol servers that expose these APIs to AI agents.

Caelus MCP Server

Remote MCP server at www.ephemengine.com.

MCP SERVER

Spectral Rules 1

Spectral governance rulesets for linting and validating these APIs. Counts are the severity each rule declares, not results of running them.

Caelus API Rules

20 rules · 18 error-severity 1 warn-severity 1 info-severity

SPECTRAL

Security Posture 1

Authentication, domain security, vulnerability disclosure, and trust-center signals.

Caelus Domain Security

TLSv1.3 · HSTS · DMARC

SECURITY

Resources

Get Started 1

Portal, sign-up, and the first successful call

GettingStarted

GettingStarted

Documentation 2

Reference material describing how the API behaves

Documentation

Documentation

APIReference

APIReference

Agent Surfaces 2

MCP servers, agent skills, and machine-readable catalogs

LLMsTxt

LLMsTxt

MCPServer

MCPServer

Design & Contract 3

Pagination, idempotency, versioning, errors, and events

Spectral

Spectral

Vocabulary

Vocabulary

Conformance

Conformance

Build 1

SDKs, sample code, and the tooling you integrate with

CLI

CLI

Access & Security 1

Authentication, authorization, and security posture

DomainSecurity

DomainSecurity

Operate 1

Status, limits, changes, and where to get help

Changelog

Changelog

Commercial 1

Pricing, plans, and the legal terms of use

PrivacyPolicy

PrivacyPolicy

Company 1

The organization behind the API

Website

Website

Other 3

Properties that don't map to a standard resource type

Hosts

Hosts

Vendors

Vendors

Playground

Playground

Source (apis.yml)

aid: ephemengine-com
name: Caelus
accessModel:
  pricing: unknown
  onboarding: unknown
  trial: false
  try_now: false
  public: false
  label: Unknown
  confidence: low
  source:
  - security
  generated: '2026-11-13'
  method: derived
image: https://www.ephemengine.com/opengraph-image?56ca3addee0d41b0
description: Caelus is a clean‑room, MIT‑licensed TypeScript suite for validated astrology computation. It computes planetary
  positions, charts, events, hellenistic timing techniques, Vedic methods, and citable chart facts across browser, edge, Node,
  and MCP clients, without Swiss Ephemeris code, AGPL licensing, or ephemeris files. The project provides a rich API for developers
  to integrate precise astrological data into applications, with extensive documentation, a playground, and a growing set
  of MCP tools for AI clients.
url: https://artifacts.apis.io/ephemengine-com/apis.yml
x-type: company
x-source: harvest:mcp-registry
x-tier: profiled
x-tier-reason: enrichment pass 2026-11-07 (modular-v1; was harvest)
specificationVersion: '0.20'
created: '2026-11-06'
modified: '2026-11-06'
tags:
- Astrology
- TypeScript
- Open Source
- MIT
- MCP
tags_raw:
- Astrology
- TypeScript
- OpenSource
- MIT
- MCP
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com
- FN: APIs.json
  email: info@apis.io
common:
- type: Spectral
  url: rules/ephemengine-com-rules.yml
- type: Vocabulary
  url: vocabulary/ephemengine-com-vocabulary.yml
- type: CLI
  url: cli/ephemengine-com-cli.yml
- type: Conformance
  url: conformance/ephemengine-com-conformance.yml
- type: LLMsTxt
  url: llms/ephemengine-com-llms.txt
- type: MCPServer
  url: mcp/ephemengine-com-mcp.yml
- type: Hosts
  url: hosts/ephemengine-com-hosts.yml
- type: Vendors
  url: vendors/ephemengine-com-vendors.yml
- type: PrivacyPolicy
  url: https://www.ephemengine.com/privacy
- type: DomainSecurity
  url: security/ephemengine-com-domain-security.yml
- type: Website
  url: https://www.ephemengine.com/
- type: Documentation
  url: https://www.ephemengine.com/docs
- type: GettingStarted
  url: https://www.ephemengine.com/docs/quickstart
- type: APIReference
  url: https://www.ephemengine.com/docs/api
- type: Changelog
  url: https://www.ephemengine.com/changelog
- type: Playground
  url: https://www.ephemengine.com/playground
apis:
- name: Caelus MCP
  description: MCP streaming HTTP endpoint providing access to ephemeris data and tools.
  humanURL: https://www.ephemengine.com/docs/api
  baseURL: https://www.ephemengine.com/api/mcp
  properties:
  - type: MCP
    url: https://www.ephemengine.com/api/mcp
  aid: ephemengine-com:caelus-mcp
- aid: ephemengine-com:ephemengine-com-api
  name: Caelus API
  description: 'Caelus API as documented publicly: 1 operations. Contract generated from the documentation by API Evangelist
    (2026-11-07); not

    the provider''s own document.'
  humanURL: https://www.ephemengine.com/docs/charts
  properties:
  - type: OpenAPI
    url: openapi/_ae-authored/ephemengine-com-openapi-generated.yml
    x-provenance: generated
x-enrichment:
  date: '2026-11-07'
  status: enriched
  artifacts_added: 15
  pass: modular-v1
  engine: identity=local,contract=local,surfaces=local,docs=local,regulatory=local

Caelus API — frequently asked questions

Does Caelus have an API?

Yes. APIs.io lists 2 APIs from Caelus, including Caelus MCP and Caelus API.

Is there an OpenAPI specification for the Caelus API?

Yes. APIs.io indexes 1 OpenAPI specification for Caelus, each linked for download from this page.

Does Caelus have an MCP server?

Yes. APIs.io lists 1 MCP server for Caelus: Remote MCP server at www.ephemengine.com.

Is the Caelus API ready for AI agents?

Caelus has a Kin Score of 20.0 out of 100 (emerging) and an Agent Readiness score of 16.4 (agent-aware), scored by API Evangelist on 2026-11-13.

Work with this as data

Every provider here is available over the APIs.io API and to AI agents over MCP.

MCP server

One button, every client — Claude, Cursor, VS Code and the rest.

https://apis.io/mcp

Tools for providers

9 MCP tools reach this

find_providersBrowse and filter every provider in the catalog.
get_provider_artifactsEvery artifact this provider publishes, grouped by type.
get_provider_operationsEvery operation across all of their OpenAPIs — one call instead of parsing every spec.
get_provider_toolsEvery MCP tool they ship, with the operation each wraps.
get_provider_evidenceHow each part of their score was established. Free — the basis for a claim should not sit behind it.
get_provider_ratingPRO — composite, band, trend and facet scores.
apis_io_searchSTART HERE — APIs, providers and tags for one query, each with its total.
resolveTurn a domain, URL or GitHub org into the provider it belongs to.
find_cohortsEvery scored population of providers in the catalog.

All 92 tools →

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