About Letvr Tools
What this site is
Letvr Tools is a collection of small, focused tools for jobs that come up every week: merging a few PDFs, working out a loan payment, counting the words in a draft, turning a spreadsheet into JSON, finding a meeting time that works in three cities. Each tool has its own page, and each page has two halves. The top half is the tool. The bottom half explains how it works, walks through real examples and says plainly where it stops being reliable.
The tools are grouped into nine categories — PDF, calculators, money and tax, text, developer, data and spreadsheets, units and numbers, time, and random and security — and the home page lists all of them. Most categories also have a longer guide that follows one complete task from start to finish.
Why everything runs in your browser
The files and text people put into online tools are often the things they would least like to hand to a stranger: contracts, bank statements, customer lists, API tokens, passwords. Most tool sites upload them to a server, process them there and send back a result. That is sometimes necessary, but for the jobs on this site it is not. A modern browser can rewrite a PDF, parse a spreadsheet, compute a SHA-256 hash or convert time zones perfectly well on its own.
So every tool here does its work inside the page. Your input is read into memory, processed by code that was downloaded with the page and handed back to you as a result or a download. Nothing you enter is transmitted, logged or stored on a server. You do not have to take that on trust: open your browser's developer tools, switch to the Network tab and use any tool. You will see the page load its own code and nothing leave with your data. Once a page has loaded, most tools keep working even if you disconnect from the internet.
How the explanations are written
A tool page that only says "enter a number and press the button" is not much use. Each page here covers four things: how to use the tool, how it works (the formula, the standard or the algorithm, with a link to the primary source), worked examples with real inputs and outputs, and the limits — the cases where the result can be wrong or surprising, such as floating-point rounding, daylight-saving changes or scanned PDFs without a text layer.
The worked examples are not typed in by hand. Every number that appears in an example is produced by the same code that runs the tool and is checked by an automated test before each release. If the code changes and an example would no longer be correct, the release fails. The English and Chinese pages are written separately rather than translated sentence by sentence: the mortgage page, for example, discusses fixed-rate US loans in English and LPR-based loans and housing-fund combinations in Chinese, because those are what readers in each language actually have.
How the tools are tested
Each tool has unit tests for its logic, using known reference values: published loan examples, test vectors from the relevant RFCs, exact conversion factors from NIST. Each tool also has a browser test that uses it the way a person would — uploading real PDF files, pasting CSV with awkward quoting, setting a time that falls inside a daylight-saving gap — and checks what comes out. Every page is checked at phone, tablet and desktop widths for layout problems, and every page is loaded with network monitoring switched on to confirm that the only outside requests are the advertising and analytics scripts described in the privacy policy.
Who maintains it
This is an independent project built and maintained by one developer, who also runs the image tools at imgc.letvr.com, a WebXR field guide at vr.letvr.com and an AI tool directory at ainews.letvr.com. It is not affiliated with Adobe, Microsoft, Google or any other company whose formats the tools work with.
If a tool gives a wrong result, a page explains something badly, or you would like a tool that is not here yet, write to miioflee@gmail.com. Reports that include the browser, the steps and — where you can share it — the input that caused the problem are usually fixed within days.
Advertising
The site is free to use and is paid for by advertising from Google AdSense. Ads appear among the explanations on tool, category and guide pages. They are not shown on the privacy policy or terms pages, and no tool requires you to click or view an ad to get its result. The privacy policy explains what the advertising code does and how to control it.