Letvr Tools

Guides

Each guide follows one real task from beginning to end, explains the decisions along the way and shows the actual numbers, using the tools on this site where they help.

PDF toolsPrepare a PDF for an upload portalTurn a pile of scans and documents into one clean PDF that an application portal will accept.CalculatorsPrepay the mortgage or invest?How to compare paying down a loan with investing the same money — with the numbers worked out.Text toolsWhy word counts disagreeWord, Google Docs and online counters give different numbers. Here is why, and which to trust.Developer toolsDebugging an API responseA walk through four common API problems: broken JSON, rounded IDs, expired tokens and wrong timestamps.Data & spreadsheet toolsCSV and Excel pitfallsWhy CSV files come out garbled, lose leading zeros or turn into dates in Excel — and how to move data safely.Unit & number convertersUnits in recipes and travelCups, ounces, Fahrenheit, miles and gallons: the conversions you meet in the kitchen and abroad, and where they trip people up.Time & productivityScheduling across time zonesFind a meeting time that works in several cities, survive the daylight saving weeks, and write deadlines nobody can misread.Random & security toolsPasswords that lastWhat makes a password strong, what current guidance says about length and forced changes, and where hashes and fair draws fit in.

A tool answers one question; a real task usually involves several. Sending an application pack means putting documents in order, turning pages the right way up, keeping the file under a size limit and checking the result. Deciding whether to overpay a mortgage means comparing two futures, each with its own assumptions. The guides below take such tasks one at a time and work through them properly.

Every number in a guide is produced by the same code that runs the tools, and is checked by automated tests before each release, so a worked example will always match what you get when you try it yourself. Each guide ends with its limits — the situations in which the advice does not hold — and links to the primary sources it relies on.

The guides are written separately for English and Chinese readers rather than translated line by line: the Chinese mortgage guide deals with LPR-based loans and housing-fund combinations, the English one with fixed-rate loans; the Chinese guide on CSV files spends more time on GBK encoding, which is the most common source of garbled spreadsheets in China.

What the guides cover

There is one guide for each group of tools. Preparing a PDF for an upload portal covers ordering, rotating, merging and splitting pages under a portal's rules. Prepaying a mortgage or investing compares the two with the same cash flows. Why word counts disagree explains the rules behind every word and character count. Debugging an API response walks through broken JSON, rounded IDs, expired tokens and timestamp units. CSV and Excel pitfalls covers encodings, lost zeros, dates and long numbers. Units in recipes and travel sorts out cups, ounces, gallons and oven temperatures. Scheduling across time zones deals with overlaps, daylight saving weeks and deadlines. Passwords that last explains strength, current NIST rules and where hashes fit.

How to use them

Each guide can be read from top to bottom, but it is also organised so you can jump to the part you need: the headings name the problem, not the tool, and the worked examples show real inputs and outputs you can repeat. Tools mentioned in a guide are linked at the top of the page, and each tool page links back to the guides that use it.

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