@useqr/core

The engine behind UseQR: QR matrix generation, a styled SVG renderer, 30+ typed payload builders, and a decode-verify loop that proves a design still scans.

MIT. Two runtime dependencies. No network calls, no telemetry, no account. Works in browsers, Node 18+, Bun, Deno, and edge runtimes.

npm i @useqr/core

Generate

import { generateSvg } from "@useqr/core";

const { svg } = generateSvg({
  data: "https://example.com",
  moduleStyle: "rounded",
  eyeFrameStyle: "leaf",
  foreground: {
    type: "linear",
    rotation: 45,
    stops: [
      { offset: 0, color: "#312e81" },
      { offset: 1, color: "#1e3a8a" },
    ],
  },
  label: { text: "SCAN ME" },
});

Eight module shapes, five eye styles (with per-corner overrides), solid/linear/radial paints, logo embedding with automatic error-correction bump, labels, and transparent backgrounds.

Typed payloads

Builders escape and validate for you, and throw a PayloadError carrying a fix string you can show a user — or hand to an agent — verbatim.

import { buildWifi, buildUpi, PayloadError } from "@useqr/core";

buildWifi({ ssid: "CafeGuest", password: "espresso", security: "WPA" });
// "WIFI:T:WPA;S:CafeGuest;P:espresso;;"

try {
  buildUpi({ vpa: "not-an-id", payeeName: "Shop" });
} catch (error) {
  if (error instanceof PayloadError) console.log(error.field, error.fix);
}

URL · text · email · phone · SMS · WiFi · vCard · MeCard · WhatsApp · Telegram · social hub · calendar event · geo · app download · UPI · PayPal · Bitcoin · Litecoin · Bitcoin Cash · Dogecoin · Dash · any BIP-21 chain · Ethereum · PIX · EPC/SEPA · Google review · menu · feedback · coupon · PDF link · JSON · Base64 · SSH/Git — plus applyUtm for campaign-tagged links.

Verify that it actually scans

The verify loop renders, rasterizes, and decodes with a real decoder (zxing), then compares against your input. Rasterization is injected because it differs per environment:

import { verifyQr } from "@useqr/core";
import { Resvg } from "@resvg/resvg-js";

const report = await verifyQr(
  { data: "hello", renderOptions: { foreground: "#cccccc" } },
  (svg, width) =>
    new Uint8Array(new Resvg(svg, { fitTo: { mode: "width", value: width } }).render().asPng()),
);
// { scannable, decoded, matchesInput, version, ecLevel, contrast, issues }

In a browser, pass a canvas-based rasterizer instead. zxing-wasm is imported dynamically inside verifyQr, so applications that only generate never download the wasm.

Print and cutting output

generateSvg({ data: "https://example.com", profile: "tiny" });

profile: "tiny" emits SVG Tiny 1.2 — no clip paths, no ARIA attributes, no properties outside the Tiny set — which is what Illustrator, print-shop RIPs, and cutting software expect.

Notes

• ESM only. From CommonJS, use await import("@useqr/core").
• Semver contract. Everything exported from the package root is public API; breaking changes to it mean a major version. Internal modules are not importable by subpath.
• Rendering is deterministic — the same input always produces byte-identical SVG, which is what lets UseQR's hosted API cache forever.

Related

• Hosted tools, keyless REST API, and MCP server: https://useqr.app
• Source and issues: https://github.com/rajkaria/useqr