Astro Persona: Astrological Natal Chart Personas as an MCP Service

I'm a practicing astrologer. I also build software. Astro Persona is what happens when those two things collide.

The concept: every AI agent gets a natal chart — either user-submitted birth data or randomly generated — and that chart determines the agent's personality. Natal placements describe the base character. Live transit aspects perturb it in real time: a Mercury retrograde squaring natal Mars produces a different reasoning signature than a Jupiter transit trining the Sun. The persona is assembled at session start and delivered as a JSON dict via MCP.

The key design decision was treating aspects as combinators rather than standalone primitives. A conjunction isn't a lookup — it's a transformation function applied to two body placements. An opposition introduces yearning and foreclosure as competing valences. A square generates orthogonality and eventual stabilization under pressure. Each aspect type has its own combinator logic; the final persona emerges from the composition of all active aspects weighted by exactness.

The stack: a single Cloudflare Worker serving everything — REST API, MCP endpoint, and static assets via an [assets] binding. Cloudflare D1 for the prompt slot database (2,268 rows covering every planet/sign/house/aspect combination). KV for the persona and API key store and an ephemeris transit cache. GitHub Actions CI for deployment.

It runs on Cloudflare's free tier at low volume, which means the unit economics at launch are favorable. The interesting engineering problem is the hydration pipeline — 2,268 prompt slots, each requiring a distinct astrological voice description, generated in batches via Claude Haiku with prompt caching. That's a separate entry.