Tools

Small, single-purpose web tools by Rahim Nathwani. Everything runs in your browser.

Learn & teach

Dot Cards (Doman) — A tool to teach toddlers numbers using dot cards.
Prime Factorization — An interactive game to practice prime factorization.
Modeling Mixture Problems — Learn to solve mixture problems with an interactive tutorial.
Distributions & Percentiles — Learn how to calculate percentiles and visualize data distributions.
Oscylinderscope — Pluck strings against a spinning striped drum and watch their sound waves freeze or drift via persistence of vision.
Excel Skills Survey — Self-assess your Excel skills and download a PDF report to share with your manager.

Berkson's Paradox — See how selection bias creates spurious correlations between independent variables.
Galton Board — Visualize publication bias: drop balls through a peg board and see how selecting only significant results distorts the distribution.
Jevons Paradox Simulator — Simulate how efficiency gains can paradoxically increase total resource consumption via the rebound effect.
Investment Challenge — Read each deal's odds, decide whether to bet and how much, and learn position sizing and the Kelly Criterion.
Monty Hall Simulator — Play the three-door game and watch how often you win track how often you switch — converging on the 1/3 vs 2/3 result.

SAT Explorer — Compare California high-school SAT scores 2017–2020: trends over time, subscores, and participation.
CAASPP Explorer — Explore California standardized test scores by school, district, and demographic group.
School Finder — Find Bay Area private schools by grade, tuition, and location.

SF POPOS Finder — Find San Francisco's privately owned public open spaces, sorted nearest first.
Lyft Bike Finder — Find nearby Lyft bike stations with real-time availability.
El Gouna Restaurant Finder — Find El Gouna restaurants by distance, cuisine, and dining type.
El Gouna Nearby Units — Find the 5 nearest El Gouna units and buildings to your location.
Zip Code Mapper — Draw polygons on a map to analyze which USA zip codes are enclosed.

PDF Diff — Show differences between two PDF files visually.
Markdown Cleaner — Clean AI-generated markdown for Google Docs compatibility.
Markdown → EPUB — Convert Markdown to a valid EPUB 3 file in your browser.
JPEG Compressor — Compress images with adjustable quality and compare file sizes.
Passport Photo Montage — Make a 3×2 montage from one photo. Print at 4×6 for six 2-inch passport photos.
DTF Halftone Knockout — Knock out the shirt color as halftone dots for breathable Direct to Film transfers.

Meeting Scheduler — Propose meeting slots and copy a message with one-click Outlook/Google calendar invite links.
Org Chart Builder — Upload an Excel file of employees and generate an org chart with SVG, PNG, and Mermaid exports.
Payment Plan Calculator — Generate NPV-based payment schedules for property purchases.