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 →1099 vs W-2
Going contract means picking up both halves of payroll tax, losing paid leave, and buying your own benefits. The rate has to move a long way to break even.
Finance💬Academic Tone Checker
Finds the casual words that cost marks in formal writing, with a replacement for each one — and leaves alone the things exam writing is supposed to have.
English🕑Age Calculator
Months are not a fixed length, so dividing days by 365.25 gives a different answer from the calendar. This uses the calendar method every official form uses.
Time🏠AC BTU Sizing
Dehumidifying needs sustained runtime. A unit that is too big hits the temperature target and shuts off before it has dried the air.
Home🛒Amazon FBA 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🏠Running Cost
A thermostat means the compressor runs about a third of the time, so the usual watts-times-hours sum overstates the cost by roughly three times.
HomeBrowse 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.
English Exams & Writing
Score conversions, writing checks and timing tools for IELTS, TOEFL and TOEIC — the parts of preparation that are arithmetic rather than practice.
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.
YouTube Creator Tools
Loop a section, pull a video ID out of any link, shift a whole subtitle file, build an embed — the small jobs that sit between filming and publishing.
Image & Photo Tools
Compress, convert, resize, crop and strip metadata entirely inside your browser. Your photos are never uploaded, because there is no server to upload them to.
Productivity & Units
Storage, speed, length, weight and paper-size conversion for the moments a spec sheet and your reality use different units.
Home & Construction
Material quantities, coverage rates and running costs for real projects — the waste factor, the rounding up to whole bags, and the units that quietly differ between the label and the job.
Latest tools
New utilities ship every week.
Stopwatch & Timer
Counting setInterval ticks loses time on every late fire. This reads the clock instead, so it stays accurate even when the tab is throttled.
Time🕑Seconds to Duration
90061 seconds is 1d 1h 1m 1s. Paste a number to format it, or type a duration to get seconds back — with the zero components dropped.
Time🕑ISO 8601 Duration
The same letter M means month before the T and minute after it. Paste a duration to see the parts, and where a conversion to seconds is genuinely undefined.
Time🕑HTTP Date Header
Expires and Last-Modified want \u201cMon, 10 Aug 2026 12:34:56 GMT\u201d \u2014 English month names, literal GMT, no milliseconds. Anything else is silently ignored.
Time🕑Hours Between Times
Writing the clock form where payroll wants decimal loses 18 minutes an entry. Overnight shifts subtract to a negative unless you handle the wrap.
Time🕑Play Test Deadline
Calculate the earliest production-access date, track the twelfth tester and see how one dropout can reset that tester's continuous-day clock.
Time🕑Epoch Rollover
It does not crash. It wraps to minus two billion and reports a date 137 years in the past, which is far harder to notice.
Time🕑Date Format Tester
In Unicode patterns YYYY is the week-numbering year. 31 December 2019 renders as 2020, which is where the New Year date bugs come from.
TimeWhy 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.