Case · Backend · TypeScript

qr-svg: QR codes from scratch

A QR-code generator that outputs SVG, in TypeScript with zero runtime dependencies: the whole ISO/IEC 18004 standard for versions 1 to 40 is written in src/qr/ (the GF(256) field, Reed-Solomon, block interleaving, 8 masks with penalties). The API returns SVG, the web demo previews, downloads SVG and PNG and checks colour contrast against WCAG.

  • TypeScript
  • Node.js 24
  • Reed-Solomon
  • GF(256)
  • SVG
  • fast-check
  • vitest
  • axe
  • Docker
  • GitHub Actions
Open the live site qr-svg.ewsir.spaceCode on request via Telegram

01 · How it looks

Screenshots

Screenshot of the project "qr-svg: QR codes from scratch" at 1280 pixels wide
Desktop, 1280 px
Screenshot of the project "qr-svg: QR codes from scratch" on a phone screen, 390 pixels wide
Phone, 390 px

02 · About

What it is and why

The task: write a QR generator with no runtime dependency and prove it is correct rather than "looks correct".

The solution: TypeScript, all of ISO/IEC 18004 for versions 1 to 40 in src/qr/: the GF(256) field, Reed-Solomon, block interleaving, patterns, 8 masks with penalties. Correctness is checked four independent ways.

Limitations

No Kanji, ECI, mixed segments, Micro QR or structured append.

There is no ready-made matrix from the standard itself in the repository: comparison with an independent implementation plays that role.

Automatic mask choice often differs from the reference (penalties are computed slightly differently), both masks are valid.

The project runs on a small VPS with demo data: no redundancy or backups.

What is inside

  • Standard references: the ISO example "01234567" in 1-M and the "HELLO WORLD" walkthrough in 1-Q match in the correction bytes; format and version words, alignment pattern positions
  • Bit for bit against the independent qrcode-generator: 12 texts × 4 levels and 80 random strings (fast-check)
  • The third-party decoder jsQR reads all 160 version × level combinations except 23-L, which the reference does not read either (the matrices are identical)
  • An own decoder checking zero Reed-Solomon syndromes; GF(256) properties under fast-check
  • 45 tests; the API returns SVG, the demo downloads SVG and PNG and checks colour contrast against WCAG
  • Result: 200 requests (a quarter heavy, version 37) p50 131 ms, p95 272 ms; RAM after the load about 180 MiB

03 · How to run

Run it locally

git clone <repository on request> qr-svg
cd qr-svg
npm ci && npm test
npm run build && npm start   # http://localhost:8121

04 · Code

The repository is private

The source is in a private repository. Message me on Telegram and I will open access.

Request the code