Miscellaneous

Things that run in your browser

Small tools, grouped by topic below. Most started with a question no existing tool answered properly. Almost all of them were built with Claude Code; the ideas, the maths and the responsibility for the mistakes are ours.

Why these exist

The questions were things like: which open-weight language model my particular GPU can actually run well, which Subway sauce works on which sandwich, what a lambda term looks like while it reduces. Some are practical calculators for a decision we had to make ourselves, others exist because the underlying maths was too interesting to leave alone.

Each tool is a single self-contained page: no account, no upload, no waiting. Whatever you type or drop in stays on your machine, which also means an image editor or e-book converter here works offline once the page has loaded. None of that is an achievement. A page that converts a file in your browser and does nothing else used to be the normal case; it stopped being one because a file converter turns out to be a good place to put ads, not because it got harder to build.

This changes nothing about which converter the first search result points at. It does mean that for us, and for anyone we can send a link to, that visit has become unnecessary.

All tools here run entirely in your browser. Nothing you enter is sent, stored or tracked.
3D Modelling (2)
  • Terrain Erosion Simulator Simulate hydraulic erosion on a heightmap, like the erosion nodes in Gaea: rain droplets carve gullies and sediment fans, with live 3D before/after preview and 16 bit PNG export.
  • Heightmap to STL Turn a grayscale heightmap (8 or 16 bit PNG) into watertight STL terrain tiles for 3D printing, with 3D preview and anti-warping options.
Language Modelling (6)
  • Token & Character Counter Paste text and count tokens, characters, words, sentences, lines and bytes live - with the o200k_base tokenizer (GPT-4o / o-series) and a colored token view.
  • Claude Code settings.json Generator Click together a Claude Code settings.json: permission allow/ask/deny rules, model, environment variables and defaults. Copy or download the result.
  • System Prompt Builder Click together a personal system prompt for your chatbot: pick a variant per aspect or leave it out, edit any block, copy the result as Markdown - in English or German.
  • Local LLM Frontier What is the best language model your GPU can run? VRAM math for weights and KV cache, honest quality bands, rough speed, and the trend: when does frontier quality arrive on your card?
  • LLM Detector Paste English or German text and get a calibrated probability that a language model wrote it - typical AI phrases marked in the text, the driving features and a Bayes factor laid open.
  • Language ZipperExperimental Paste a sentence and a character model trained on 87 languages says which one it is - plus a family tree and a map of those languages built from nothing but how cheaply each explains the others. Programming languages too.
Playground (5)
  • A Model of PsychohistoryExperimental Posterior predictive futures of a galactic civilization - a coupled stochastic model with priors, interventions, credible bands and a few hundred thousand world-lines.
  • Ruler Title Finder You are newly in power and need a title. Seven questions, a transparent fit score, and 44 historical ruler titles with real history: etymology, notable holders, occupational statistics, and how each ended.
  • Reaction Diffusion Two chemicals, four numbers and a full screen. Drag a cursor across the feed/kill plane and watch the pattern turn from solitons into worms into cells that divide, or paint new seeds into it with the mouse.
  • Ripple Tank A live wave simulation, full screen: a plane wave rolls in from the left, you drop in slits, lenses and prisms or paint walls and glass freehand, and diffraction and refraction happen because the wave equation says so.
  • Sun over Regensburg Will the sun still reach this spot tomorrow at 20:15? Click anywhere on the map of Regensburg and the official surface model answers for that exact point, buildings and trees included, down to a metre. Hours of sun per day and per year come as maps of their own, and the whole day can be exported as a film.
Concepts, Visualised (2)
  • Lambda Diagrams Type a lambda-calculus expression, see it drawn as a Tromp diagram, and watch beta reduction morph it smoothly, step by step. Church numerals, combinators and your own terms.
  • Input Shaping Calculator Driving a damped spring-mass system without residual vibration: ZV/ZVD/ZVDD/EI shapers, step response and sensitivity curve.
For Parents (8)
  • Name Finder Browse and filter hundreds of german baby names.
  • Parental Leave Planner for Germany (Elterngeld) A month-by-month grid over 24 life months where both parents assign Basis, ElterngeldPlus or Partnerschaftsbonus months by clicking cells, with total payout, German income tax under the progression clause and a Pareto front of time against cost.
  • Pregnancy Timeline Maps pregnancy symptoms over pregnancy weeks. Also risk curves for miscarriage probability and premature birth survival.
  • Child Development Timeline Visualizes developmental milestones across domains. Overlaid with WHO percentile growth charts for weight and height.
  • Honest Due Date Calculator Models the birth date as a skew-normal distribution with an evidence-based expected due date, based on multiple factors.
  • Birth Decisions ExplorerExperimental Explore the choices around birth: selecting an option live-locks incompatible ones and explains why. Quantified effects, an evidence traffic-light per statement, and a generated birth-plan draft for the midwife conversation.
  • Infographic: Baby Sleep, Feeding & Crying Total sleep and longest continuous night stretch, feeding frequency (breast vs. formula), and crying and fussing duration per day.
  • Infographic: Daycare Infections Infections per year and sick days per year, shown as P10–P90 bands.
Books (3)
  • Book Recommender Rate the fantasy & sci-fi books you know and get recommendations with calibrated probabilities, a taste map and much more.
  • E-Book Converter Convert EPUB, MOBI, AZW3, Markdown, HTML and plain text into nine formats, one file or a whole batch.
  • Narrative ChartExperimental Drop in an English novel and get the xkcd storyline diagram of it: one line per character, bundled while they share a scene.
Images (2)
  • Image Editor Crop, scale, rotate, draw, add text and warp the four corners - built on a non-destructive operation stack you can reorder and roll back like a CAD history.
  • Color Extractor Find out which colors a photo or logo is really made of, and copy them as hex, CSS or JSON: eight palettes from two to nine colors, each with its share of the image and a preview of the picture reduced to it.
Music (4)
  • Choir Part TrainerExperimental Practise your own part from a MusicXML or MIDI score: your voice loud and the rest quiet, slower tempo, transposition, a count-in and a loop over the four bars that never work, with scrolling notation, a piano roll of all voices and live pitch feedback that also tells you when you have landed in the wrong voice.
  • Sheet to MIDIExperimental Upload a PDF of cleanly engraved choir music and get practice MIDI back: optical music recognition entirely in your browser, per-voice playback (one voice alone, all, or one loud and the rest quiet), suspect measures flagged for proofreading, export as MIDI and MusicXML.
  • Sing TrainerExperimental Practice hitting the right notes: scrolling sheet music, live pitch detection from your microphone, generated melodies, scales and hold-the-note drills for every voice type.
  • Vowel Map See which vowel you are actually singing: the first two formants are estimated live from your microphone by LPC and your voice wanders as a point through the vowel chart. Calibrating on your own corner vowels makes two singers comparable, snapshots and a target vowel help with vowel blending in a choir.
Everything Else (4)
  • Drug Concentration Visualiser Pharmacokinetic blood-level curves: drag intake times, combine doses and immediate/extended-release forms, and watch steady-state accumulation.
  • Race Time Predictor Enter your running PBs (10K, marathon, …) and get predictions for every other distance - Riegel formula with a personally fitted fatigue exponent.
  • Subway Sauce Guide Which sauce goes with which Subway sandwich? Heatmap with switchable color scale.
  • Leverage & Ruin How much leverage is too much? Monte Carlo simulation of a leveraged ETF over long horizons: volatility drag, the Kelly optimum, break-even leverage and wipe-out probability, fat-tailed daily returns and crash shocks that end a leveraged position in a single day. The average outcome rises without limit while the typical path peaks and turns back down.