Free developer tools.
A small family of focused, free, in-browser tools that explain confusing developer syntaxes in plain English. No signup, no upload, no tracking of your content.
On this site
📖 Regex explainer
Paste any regex, get a plain-English breakdown. Try it →
📚 Patterns library
Curated, rigorously tested regex patterns for common use cases. Browse →
📋 Regex cheat sheet
Every regex token, class, group, and flag on one printable page. View →
Sister sites & recommended tools
Other small, focused, free in-browser tools we like and recommend. Same philosophy: do one thing well, explain it clearly, no signup.
⏰ crontabsheet.com
The sister site. Cron expression explainer, builder, English-to-cron translator, and platform tools for AWS, GitHub Actions, Kubernetes, Quartz, and more.
📐 Square footage calculator
Calculate area in square feet for rooms, lots, or any rectangular space — handy for flooring, paint, and real estate.
％ Percentage calculator
Everyday percentage math — increase, decrease, "what percent of X is Y", and more.
🎂 Age calculator
Calculate exact age in years, months, weeks, and days between any two dates.
🔤 Base64 encode / decode
Encode strings or files to Base64, or decode Base64 back to plain text — all in your browser.
🔗 URL encode / decode
Convert URLs and query parameters to and from percent-encoded form for safe transmission.
🔒 Password strength checker
Estimate how strong a password is and how long it would take to crack — entirely client-side.
📝 Word counter
Count words, characters, sentences, paragraphs, and reading time for any text.
🆔 UUID generator
Generate UUIDs (v1, v4, v7, and others) one at a time or in bulk, with explanations of each version.
🧰 JSON tools
Format, validate, minify, and convert JSON. The Swiss-army knife for JSON in the browser.
#️⃣ Hash generator
Generate MD5, SHA-1, SHA-256, SHA-512, and other hashes from any input text.
⏱️ Epoch time converter
Convert between Unix epoch timestamps and human-readable dates across any timezone.
🔁 Text repeat
Repeat any string a given number of times — useful for testing, mock data, and load tests.
📏 Unit cheatsheet
Engineering and scientific unit reference — converters, cheat sheets, and printable charts for length, mass, energy, and more.
⏰ Hours calculator
Free hours and timesheet calculator with overtime and pay. Handles breaks, overnight shifts, and decimal hours.
🕐 Clock with us
Online alarm clock, timer, stopwatch, world clock, and time zone converter — all browser-based, no signup.
💹 Margin vs markup
Convert between profit margin and markup, find break-even, and factor in platform fees, shipping, and tax.
📦 Box volume calculator
Calculate the volume of a box from its length, width, and height in any units — for shipping, storage, and packing.
⚖️ DIM weight calculator
Dimensional (billable) shipping weight for FedEx, UPS, USPS, DHL and more carriers, with up-to-date divisors.
📐 Girth calculator
Parcel length-plus-girth against carrier size limits, plus body circumference measurements for fitness tracking.
☀️ Solar calculator
Free, unbiased solar and off-grid calculators — system sizing, savings and payback, and battery banks.
🔠 Case transformer
Convert text between Title Case (AP, Chicago, APA, MLA), sentence case, camelCase, snake_case, kebab-case, and more.
🌐 CIDR calculator
Calculate, split, and visualize subnets. IPv4/IPv6, VLSM planner, cloud-aware reserved IPs, and Terraform export.
🖧 Subnet mask calculator
Network and broadcast addresses, usable host range, wildcard masks, and VLSM planning for IPv4 and IPv6.
🖼️ Picture toolkit
Browser-based image tools — compress, convert, resize, crop, and watermark. Files never leave your device.
🧹 Remove metadata
Strip EXIF, GPS, and hidden metadata from images, PDFs, and Office files — locally in your browser.
🏦 EMI calculator (India)
EMI calculator for home, car, and personal loans in India, with full amortization schedules and prepayment impact.
💰 Total interest calculator
Find the total interest paid over the life of any loan, comparing terms and rates with a full amortization schedule.
📈 SIP calculator
Project mutual-fund SIP returns, step-up SIPs, and goal-based investing, with maturity value and wealth-gain charts.
🎓 GPA calculator
Compute semester and cumulative GPA on 4.0 and weighted scales, converting letter grades and percentages.
½ Fraction calculator
Add, subtract, multiply, and divide fractions with step-by-step working, simplification, and decimal conversion.
🍎 Calorie calculator
Estimate daily calorie needs, TDEE, and macros from your goals — BMR-based targets for loss, maintenance, or gain.
⚕️ BMI & BMR calculator
Calculate BMI, BMR, and daily calorie needs in one place, in metric or imperial, with healthy-weight ranges.
❄️ AC tonnage calculator
Size an air conditioner by room area, climate, and occupancy — BTU and tonnage estimates for homes and offices.
🛢️ Tank volume calculator
Volume and fill level for cylindrical, rectangular, and oval tanks — horizontal or vertical, in litres or gallons.
🧱 Cubic yardage calculator
Calculate cubic yards for concrete, mulch, gravel, soil, and sand from your dimensions in any units.
🏊 Pool volume calculator
Pool volume in gallons or litres for rectangular, round, and oval pools, with dosing help for chemicals.
🏗️ Concrete material calculator
Estimate concrete volume plus cement, sand, and aggregate quantities — slabs, footings, and bags by mix ratio.
🏠 Roofing material calculator
Calculate roofing squares, shingle bundles, and underlayment from area and pitch, with a waste factor.
🪜 Stair calculator
Work out stair rise, run, stringer length, and headroom to code, with diagram output for carpentry.
🧰 Construction calculators
A hub of construction calculators — concrete, framing, drywall, paint, and more, with material estimates.
⚡ Voltage drop calculator
Calculate voltage drop and correct wire size for AC and DC circuits, with NEC and IEC formulas.
🔋 Solar battery bank calculator
Size an off-grid battery bank from daily load, autonomy days, and depth of discharge, with lithium presets.
🔌 Backup power calculator
Estimate UPS and generator runtime from load and battery capacity, for home, office, and server racks.
🍳 Cooking measurement converter
Convert cooking measurements between cups, grams, ounces, and millilitres, with recipe scaling.
🔢 Number to words
Convert numbers to words for cheques, invoices, and legal documents, with currency wording support.
📄 PDF tools
Merge, split, compress, convert, and rotate PDFs in your browser — no uploads, files stay on your device.
🎨 Color code kit
Pick colors and convert between HEX, RGB, HSL, and CMYK, with palettes, contrast checks, and CSS values.
🔳 Barcode & QR generator
Generate QR codes and barcodes (Code 128, EAN, UPC), downloadable as PNG or SVG for print and labels.
📶 Internet speed test
Test your download, upload, ping, and jitter right in the browser — quick, accurate, no app to install.
📡 What is my IP
See your public IPv4 and IPv6 address, ISP, and approximate location, plus headers and connection details.
🔍 WHOIS lookup
Look up domain WHOIS, registrar, name servers, expiry dates, and DNS records for any domain.
What's coming
More patterns. More long-form guides. A flavor converter that ports a regex from PCRE to JavaScript (or any other flavor pair) and tells you what changed. A ReDoS / catastrophic backtracking detector.
If there's a specific developer-tool gap you'd like filled, tell us.