Small tools that
answer one question fast.
ecech. is a growing library of free, single-purpose online calculators and developer utilities. No signup, no clutter, no data collection — every tool runs entirely in your browser.
Popular right now
See all →Foreign Transaction Fee Currency Converter
Live mid-market rates, then your card's foreign transaction fee and the issuer's conversion margin added on top — so you see the number that actually hits your statement.
Finance💻JSON Formatter and Validator with Error Line Numbers
Paste broken JSON and get the exact line and column that failed, with a human explanation of what the parser expected. Format, minify, sort keys and copy out.
Developer✏️Keyword Density Analyzer with Stop Word Filtering
Strip the stop words, then see which terms and phrases your page actually leans on. One, two and three-word density with an over-optimisation warning.
Text & SEO🌐Strong Password Generator with Entropy Readout
Generated with your browser's cryptographic RNG, scored in bits of entropy rather than a vague coloured bar, with crack-time estimates for four attacker budgets.
Network🕑Meeting Time Finder Across Three Timezones
Pick three cities and a working window, and see every hour scored green, amber or red for all of them at once — with real IANA timezone data, so daylight saving is handled.
Time🛒Amazon FBA Fee and Net Profit Calculator
Referral fee, fulfilment fee by size tier, monthly storage, returns and ad spend — subtracted in the order Amazon actually applies them, down to profit per unit.
E-commerceBrowse by category
Ten focused collections, each built around a specific job to be done.
Financial & Currency
Currency conversion with real fees baked in, loan and interest maths, margin and payroll checks — the numbers that decide whether a deal is worth doing.
Developer & Code
Formatters, validators, encoders and generators that save you from installing another dependency just to check one string.
Text & SEO Content
Counters, case converters, density analysers and readability checks for anyone whose words have to hit a limit or rank on Google.
Network & IP
Subnet maths, IP lookups, encoders and password generation — the sysadmin sidebar you keep open in a second tab.
Date, Time & Timezone
Timestamps, business-day maths and meeting windows that actually respect daylight saving in every city involved.
E-commerce & Pricing
Landed cost, marketplace fees, break-even discounting and ad profitability — pricing tools that subtract before they add.
Math & Statistics
Percentages, averages, deviation, significance and ratio maths, each with the working shown rather than just an answer.
Design & Color
Colour conversion, contrast auditing, palette building and CSS generators that output code you can paste straight into a stylesheet.
Health & Fitness
Body metrics, energy balance, hydration and pace calculators using published formulas, with the assumptions stated openly.
Productivity & Units
Storage, speed, length, weight and paper-size conversion for the moments a spec sheet and your reality use different units.
Latest tools
New utilities ship every week.
MB to GB Converter with Decimal and Binary Modes
The reason your 1 TB drive shows 931 GB, settled. Convert in base-10 or base-2, see both answers side by side, and find out which one your operating system uses.
Converters🏃TDEE Calculator with Honest Activity Multipliers
Mifflin-St Jeor BMR with activity levels described by what your week actually looks like, not by adjectives. Includes a deficit planner and the error range stated openly.
Health🎨WCAG Contrast Ratio Checker for AA and AAA
Test any foreground and background pair against every WCAG threshold at once, with a live preview and a one-click suggestion for the nearest passing colour.
Design📊Percentage Increase and Decrease Calculator
Four related questions in one place — change between two numbers, apply a percentage, find the original, and see the working written out so you can check it.
Math🛒Amazon FBA Fee and Net Profit Calculator
Referral fee, fulfilment fee by size tier, monthly storage, returns and ad spend — subtracted in the order Amazon actually applies them, down to profit per unit.
E-commerce🕑Meeting Time Finder Across Three Timezones
Pick three cities and a working window, and see every hour scored green, amber or red for all of them at once — with real IANA timezone data, so daylight saving is handled.
Time🌐Strong Password Generator with Entropy Readout
Generated with your browser's cryptographic RNG, scored in bits of entropy rather than a vague coloured bar, with crack-time estimates for four attacker budgets.
Network✏️Keyword Density Analyzer with Stop Word Filtering
Strip the stop words, then see which terms and phrases your page actually leans on. One, two and three-word density with an over-optimisation warning.
Text & SEOWhy ecech. exists
Most online calculators are the same three form fields wrapped in six advertisements and a cookie wall. They answer the textbook version of a question and ignore the version you actually have: not “what is 100 USD in euros” but “what will my card actually charge me after the foreign transaction fee”; not “what is 30% of 40” but “what discount can I run and still clear my target margin after marketplace fees”.
Every tool here is built around one of those realistic questions. Each one loads as a single self-contained page, runs entirely in your browser, keeps no account, sets no tracking cookie and sends none of your inputs to a server. Each one also shows its working — the formula, the assumptions and the edge cases — so you can check the result rather than trust it blindly.
- One job per page. No mega-calculator with 40 tabs.
- Real-world inputs. Fees, taxes, rounding and regional variants included where they matter.
- Shown working. Formulas and assumptions are printed next to the answer.
- Fast everywhere. Single file, no framework, usable on a phone on bad hotel wifi.