How I built a browser-only face-rating app with Next.js + MediaPipe (no upload, $0 per scan)

Most "rate my face" tools do one of two sketchy things: they upload your selfie to a server, or they bill an AI vision API on every single scan. I wanted neither. So when I built ships a FaceLandmarker that runs on WebGL and returns 478 3D landmarks per face — entirely client-side. I self-host the model + wasm so there's no third-party CDN call (and it loads fine from regions where Google's CDN is flaky):

import { FaceLandmarker, FilesetResolver } from "@mediapipe/tasks-vision";



const vision = await FilesetResolver.forVisionTasks("/mediapipe/wasm");

const landmarker = await FaceLandmarker.createFromOptions(vision, {

  baseOptions: { modelAssetPath: "/mediapipe/face_landmarker.task" },

  runningMode: "IMAGE",

  numFaces: 1,

});



const result = landmarker.detect(imageElement);

const pts = result.faceLandmarks[0]; // 478 points, each {x, y, z} normalized 0..1

That pts array is everything I need. The image element is read straight from an <input type="file"> and a canvas — it never gets POSTed anywhere.

Step 2: turn coordinates into metrics

Every metric is "how close is this to an ideal, within a tolerance." So the core helper is just a clamped closeness function:

const clamp01 = (x: number) => Math.max(0, Math.min(1, x));

// 1.0 = exactly ideal, 0.0 = a full tolerance away or worse

const closeness = (deviation: number, tolerance: number) =>

  clamp01(1 - Math.abs(deviation) / tolerance);

Symmetry — reflect the left-side landmarks across the face's vertical midline and measure how far they miss their right-side partners:

function symmetry(pts) {

  const midX = (pts[33].x + pts[263].x) / 2; // midpoint between outer eye corners

  let totalDev = 0;

  for (const [l, r] of MIRROR_PAIRS) {

    const reflectedLeftX = 2 * midX - pts[l].x;

    totalDev += Math.abs(reflectedLeftX - pts[r].x);

  }

  return closeness(totalDev / MIRROR_PAIRS.length, SYMMETRY_TOL);

}

Facial thirds — forehead-to-brow, brow-to-nose-base, nose-base-to-chin should be roughly equal. Score the deviation from a perfect 1:1:1.

Facial fifths — the face should be about five eye-widths wide. Score the variance across those five segments.

Canthal tilt — the angle from inner to outer eye corner (a positive/upward tilt reads as "more attractive" in most studies). Computed per eye, then I penalize asymmetry between the two.

FWHR — facial width-to-height ratio, bizygomatic width over upper-face height.

Step 3: weight them into one score

Different metrics matter differently, so it's a weighted blend, then scaled to 0–10:

const dims = [

  { key: "symmetry", weight: 0.30 },

  { key: "thirds",   weight: 0.25 },

  { key: "fifths",   weight: 0.20 },

  { key: "tilt",     weight: 0.15 },

  { key: "fwhr",     weight: 0.10 },

];



const score10 =

  dims.reduce((sum, d) => sum + metrics[d.key] * d.weight, 0) * 10;

Because it's deterministic, the same photo always yields the same score — which, for a "rate me" tool, matters a lot for trust. (Vision-LLM scores drift between runs; geometry doesn't.)

Step 4: the part that does cost money

Numbers alone are a bit cold, so the paid tier sends the photo to a vision LLM once and gets back a written reading — archetype, personality notes, and a constructive, non-surgical "glow-up" direction. That's the only path where the image leaves the device, and it's gated behind a credit so the cost is covered. I keep the prompt firmly on the "fun + self-reflection" side and refuse anything that infers race/age or pushes surgery.

Lessons

• 
  Push the deterministic, cheap work to the client. It made my free tier genuinely $0 and privacy-preserving instead of a loss leader.


• 
  Self-host MediaPipe assets. Saved me from CDN reliability issues and a third-party request on every visit.


• 
  Reproducibility builds trust more than a fancier-but-wobbly score.

— upload a selfie and the geometry score comes back in a couple of seconds, all in your browser. Happy to answer questions about the MediaPipe or scoring bits in the comments.