Antumbra
A voice with rules, and a checker for every rule — so the model can't drift into jargon, flattery, or claims nobody can check.
antumbra.space ↗︎
Four systems, one straight answer.
Western astrology, bazi, zi wei dou shu, and six questions about this particular relationship. When they disagree, the questions win. Black, white, and nothing in between — the whole product sits inside one CRT.
- Role
- Product, interface, AI behaviour, code — one person
- Status
- Live · closed testing
- Built in
- 7 days · 72 commits
- Model's job
- Writes the sentence. Decides nothing.
- Checks
- 22 scripts, one per rule
- Stack
- Next.js 16 · Neon Postgres · Claude
- score
- 78
- phase
- 0.71
- flag
- initiating is one-sided
- direction
- holds
You do the reaching, and you aren't tired afterwards — which is the part that matters.
- jargon
- model tells
- echo of one answer
- contradicts the numbers
- unfalsifiable
- repetition
The code decides what. The model only writes it.
Score, position, flag, direction — computed, none of it passes through a language model. The model gets a finished conclusion and makes it read like a person wrote it.
None of this passed through a model. The model gets it as a brief and writes.
A working model of the review layer. The checks are the product's real rules — the jargon table, the model-tell patterns, “built from one answer is an echo” — running here in the browser; the model's drafts and rewrites are scripted. Switch a checker off and run it again to see what ships.
A rule without a checker isn’t a rule. It’s a hope.
Press Write it. The checks are the product’s real ones, running in your browser. Switch one off and see what ships.
One script per rule.
If a rule matters, there is a command that fails when it’s broken. Voice, numbers, page — twenty-two of them.
The map, centred on you. Positions are computed, not draggable. Phase is how much a relationship gives back; size is how often you're in touch; a flat orbit swings close and distant. Redrawn from the demo account's real geometry.
The map, centred on you.
Phase is how much a relationship gives back. Size is how often you’re in touch. A flat orbit swings close and far. Positions are computed, not draggable.
- Change 01
“My best friend and I scored so low, I want to retake it.”
Wrong · The score came almost entirely from two birth charts. Not one of her answers about the relationship went in.Now · Driven by the answers, chart as a correction. 0 and 100 are both reachable. - Change 02
Every reading found a flaw — even the ones that scored 90.
Wrong · “What to watch” was a required field in the output shape. A flaw was decided before any data was read.Now · Follows a computed list. Empty list → it writes the boundary and invents nothing. - Change 03
You answer that you always reach out first. It tells you that you always reach out first.
Wrong · A conclusion built from a single answer reads like a finding and carries no information.Now · Hard rule: one input can't become a line. It has to cross two, or come from the computed layer.
The ruler changed three times.
Every change is written down in public under What changed, and each entry has to say what the previous version got wrong.
- 1Aug 29 · First commit: cover, forms, charts, verdict, map. Called Verdict.
- 2Aug 30 · Renamed Antumbra. Privacy and terms. Gazetteer rebuilt.
- 3Sep 02 · Review layer for the voice. Score redefined: 0 and 100 reachable.
- 4Sep 03 · Echo rule: one answer can't become a finding. Cover opened to everyone.
- 5Sep 04 · Repetition checker. About, How it works, Pricing. Closed testing.
Seven days from first commit to closed testing.
Next.js 16, Drizzle on Neon, next-auth. The hard layer is deterministic — astronomia, lunar-javascript, iztro, a gazetteer. The soft layer is Claude, given a fixed conclusion and asked only to write it.
What I'd do next
- 01Open the closed testFifty readers, and the first ‘What changed’ entry written from someone else’s complaint rather than mine.
- 02A regression set for the voiceEvery rewrite the review layer has ever made, kept as a test — so a prompt change can’t quietly bring the jargon back.
- 03Make the map say whyTap a person, see the three numbers that put them there. The position is already computed; it should be able to explain itself.