Lumen Lab 루멘랩

About

Lumen Lab is a small, one-person software studio

We make phone games, apps and free web tools that work right in your browser. This page covers who makes them, what each tool checks and how the sites pay for themselves.

Who we are

Lumen Lab (루멘랩) is a sole proprietorship based in Korea. One person plans and runs it, and fixes what readers report by email.

Name
Lumen Lab (루멘랩)
Type
Sole proprietorship
Email
contact@lumenlab.page
Phone
+82-70-8098-5263

What we have made so far

  • 12 web tools Date, number and pay calculators, a character counter, file conversion, printable calendars, QR codes, device tests, timers, typing practice and fair picks. All free, no sign-up. See the tools
  • 49 English guides Explainers on the tricky parts of each tool and the rules behind the numbers. They are all collected in this site’s Guides.
  • 1 game Chick Rescue (Out now). For phones, on Google Play and the App Store. See the game
  • 1 app SetNote (Available now). See the app

How we build the tools

  • Ready to use. No sign-up, nothing to install, no daily limits.
  • Your input stays on your device. Dates, text, name lists and files are worked on inside your browser and never sent to a Lumen Lab server. There is no server that receives them.
  • Rules and sources are shown. Where the answer depends on a rule (spaces in a character count, a holiday falling on a weekend, 6÷2(1+2)), the page says which rule it uses, and numbers that come from laws or official data show their source and the date we checked.
  • Calculators and counters are checked against separate answers. The counting and calculating code is kept apart from the page and tested automatically against reference values worked out another way. What each tool checks is listed just below.
  • Limits are written down. What a web page cannot know, features that don’t exist yet and things we could not verify are stated on the tool and its About page.
  • No made-up numbers. We don’t publish user counts, ratings or testimonials we haven’t verified.

What each tool checks and discloses

This gathers what each tool’s About page says. Follow a tool’s name to try it here, or “Rules and sources” for the full details on the tool’s own site.

Daycount Days between dates, age and business days
It is tested automatically against more than 3,200 answers worked out separately with Python’s date library. Rules and sources
Scientific Calculator Scientific functions and physical constants
Results are compared automatically with about 3,700 answers computed separately in Python (sympy, mpmath, scipy and numpy), and the physical constants were checked digit by digit against the NIST table. Rules and sources
Takehome Korea Korean take-home pay and severance
Rates and limits are taken only from laws and agency notices opened directly, and every figure is listed with its source and the day it was checked. Severance pay matches the Ministry of Employment and Labor's worked example to the last jeon (₩88,641.31 average daily wage). Rules and sources
Inplace Image, video and PDF converter
Files are converted inside your browser and never uploaded. The open-source libraries that do the work (Mediabunny, LAME, libheif, PDF.js, pdf-lib, qpdf, SheetJS and more) are all named on its About page. Rules and sources
Staycode QR code maker
It makes static codes only, so the link lives inside the image and keeps working even if Staycode stops. Every code is read back right away to check that it scans. Rules and sources
Onesheet Printable calendars and holidays
US federal holidays for 2026 and 2027 were checked day by day against the Office of Personnel Management schedules, Korean holidays against the official announcements, and weekdays are tested for every day from 1900 to 2100. Rules and sources
Kankan Character counter
The counting code is covered by about 35,000 automated tests, with expected values taken from Python's codecs and Unicode libraries, the twitter-text package and three independent SMS calculators. Rules and sources
Pickboard Wheel, ladder and team picker
Every pick starts from a fresh seed from the browser's crypto.getRandomValues(), and more than 500 automated tests, including chi-square checks over 100,000 draws, confirm that results come out even. A result link lets anyone recompute the same result. Rules and sources
Todok Korean and English typing practice
The way speed and WPM are counted is published, and the practice texts contain no books, articles or lyrics. Rules and sources
Oneturn Timer, stopwatch and world clock
City times come from the IANA time zone database, with the 2026 rule changes for Canada, Morocco and Cuba applied separately, and the tests compare every city with Python's zoneinfo. Rules and sources
Checkbench Keyboard, mouse and mic tests
Each verdict shows its threshold (30 ms for keyboard chatter, 50 ms for double-clicks and so on), and what a web page cannot see, such as a mouse's true USB polling rate, is stated plainly. Rules and sources
Fewmoves Chess openings by rating, with a trainer
The numbers are our own count of the October 2026 rated games Lichess publishes, and every line in the guides is played through with chess.js when the site is built, with traps marked as mate checked to be checkmate. Rules and sources

Keeping things current

Some of the rules the tools follow change every year, so updates are planned around when they change.

  • Takehome Korea New social insurance rates, contribution limits and the withholding table are added when they are published. For 2027 it already separates what is set, what is approved and what is not decided yet.
  • Onesheet Korean holidays are switched to the official almanac once it is published each year (around late June). Until it is out, that year is marked “not yet official”.
  • Oneturn Changes to daylight saving or time zone rules are added as countries make them, like the 2026 changes in Canada, Morocco and Cuba.
  • All tools If you report a wrong result, we check it and fix it. When a guide changes, it shows the date it was updated.

Ads and running costs

  • The web tool sites and this site’s guides are paid for by Google AdSense ads. The tools and guides are free.
  • This site’s home, product pages, guide index, About and Privacy pages, and the app support and privacy pages carry no ads.
  • How ads, cookies and visit statistics work is explained in the privacy policy.

Found a wrong result, or want a feature? Email us

Tell us which tool, your device and browser, and what you entered, and we can check it faster. Phone: +82-70-8098-5263 (in Korean).

Write an email See what we make