Pheno
A genetics co-pilot for Horse Reality — built as a browser extension and a companion web app.
Developed by Engine Room
Overview
Pheno reads the genetics a player already has access to inside Horse Reality — a long-running online horse-breeding simulator — and turns raw allele strings into decisions a breeder can actually act on: what colour a foal will be and at what odds, whether a planned cross carries a lethal gene, how a horse will perform across seven competition disciplines, and what a horse is worth on the market.
It runs in two places. A Chrome extension overlays the game itself, so the analysis appears in-context on the pages players are already looking at. A Next.js web app handles accounts, saved collections, breeding goals, and the cross-device sync the extension reads from.
The problem it solves
Horse Reality exposes a horse's genotype as a compact string — something like EE aa gg CRn. Experienced breeders learn to read these by hand, but the real work is combinatorics: cross two horses and you're mentally multiplying two sets of alleles across fifteen-odd colour loci, weighing dilutions and modifiers, and remembering which gene pairings are lethal. Doing that reliably, for every prospective pairing, is exactly the kind of bookkeeping a computer should be doing.
Pheno does that bookkeeping. For a single horse it names the exact coat colour, lists what each gene will pass to a foal and at what probability, and flags carried lethal alleles. For a pairing it cross-multiplies both parents into the full distribution of possible foals with probabilities, computes the coefficient of inbreeding from the pedigree, estimates covering-success and fertility, and warns before a lethal cross.
Beyond colour, it grades conformation and genetic potential into projected ability across dressage, driving, endurance, eventing, flat racing, show jumping and western reining — and on the market it surfaces that same analysis inline on listings, so a buyer can judge a horse without ever opening it. Every number a serious breeder would otherwise compute on paper, computed instantly and in-place.
How it works
A pure genetics engine at the core
The heart of Pheno is a dependency-free genetics engine — no DOM, no network, no I/O. It parses Horse Reality's genotype strings into typed genotypes, then resolves them across all ~15 coat-colour loci (extension, agouti, grey, cream, dun, champagne, silver, mushroom, the white-spotting family, tobiano, sabino, splashed white, frame overo, roan, leopard complex) to derive canonical colour names — matched against 200+ named colours from the game's own wiki — pass-on odds, full foal distributions, Wright's coefficient of inbreeding, and lethal-gene alerts. Keeping this layer pure is what makes it trustworthy: it's covered by an extensive Node test suite and powers both surfaces from a single source of truth.
Conformation, potential & market analysis
On top of genetics, Pheno reads a horse's 10 genetic-potential stats and 12 conformation areas (plus breed-specific gaits like tölt and flying pace), refines them with the game's own Breeder's Advice, and blends potential and conformation into a projected discipline rating — lazy-loaded into market listing rows as they scroll into view, exactly where a buying decision is made.
Image-based coat detection
Some modifiers aren't in the genotype string — they're only visible on the horse. Pheno samples the passport image pixel-by-pixel to auto-detect sooty and flag flaxen and pangaré as possible, while suppressing false reads when roan, grey or heavy white spotting would confound the brightness signal.
Privacy-first analytics
Anonymous by default — no personal profile, no horse IDs, no PII unless a user signs in and opts in. The extension skips bundling the full PostHog SDK entirely, posting events to the capture endpoint directly to keep the payload tiny.
Engineering choices — and why
Results
Engineering & delivery
- Production builds land consistently in ~27–34s.
- Exhaustive automated test suite — the test directory is the single largest area of the codebase.
- Shipped and live: web app on Vercel, extension published to the Chrome Web Store.
Adoption
- 30 extension installs to date, 20–30 monthly active breeders, 19 daily active users.
- 58 visitors on launch day.
- 100% retention across the first two weeks live — every breeder who tried it kept using it.
Pheno turns Horse Reality's raw genotype strings into instant, in-context breeding decisions — a pure, exhaustively-tested genetics engine shared across a Manifest V3 Chrome extension and a Next.js web app, shipped continuously on Vercel.
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