📝 Notes
93 articlesWas the file tampered with? A one-minute MD5 check
A backup job exited 0, yet two months later the archive reported unexpected end of archive. This note explains what MD5 and SHA-256 can and cannot prove, with hash commands for each platform and how to keep a backup manifest.
Rejected payment forms: Chinese uppercase amounts and the usual mistakes
A cheque for 20,500 written out in Chinese uppercase characters came back with one comment: a zero is missing. This note follows the annex to the Payment Settlement Measures to cover the uppercase digit table, when to write the zero character and the whole-amount character, date rules, and how inconsistent amounts affect cheques versus settlement vouchers.
Masking phone numbers and ID numbers by hand is too slow
A support log carried four real phone numbers and an ID number, and it was already too late to recall. This note gives a masking rules table for number fields, a three-step process for image redaction and pre-send checks, and several practices that look like redaction but are not.
How far can you compress an image before it blurs? Lossless, WebP and page speed
A registration system wants a one-inch photo under 500 KB, but the phone produces 6.1 MB. This note breaks image size into three layers, pixel count, encoding quality and attached data, gives settings for shrinking dimensions before quality, and covers format choices for transparent images and screenshots.
Why Base64 images can be slower: where Data URI inlining pays off
A listing page took nine seconds because large product images were inlined as Data URIs in the API. This note explains that Base64 is encoding rather than encryption, why it adds a third to the size, and at what scale inlining actually pays off.
Unix timestamps that do not match the date: seconds, milliseconds and time zones
An order timestamp showing 1970 usually means a 10-digit seconds value and a 13-digit milliseconds value were mixed up. This note walks through digit count, time zone and boundary checks, with language-specific examples and notes on the 2038 overflow.
Inside the Notes section: tool tests, lessons learned and a category guide
The Notes section holds 58 articles across tech notes, life essays and resources. This page explains how articles differ from tool pages, what each category covers, and how to search by problem when you cannot recall a tool name.
Missing comma in JSON? Locating the error, minifying and escaping
Hand-written JSON configs throw syntax errors with no obvious location, and API responses often arrive minified into one line. This note covers common invalid forms, the exact error messages two tools produce, how to convert line and column numbers, and measured indentation size differences plus escaping layers on a 191-key sample.
Auto-increment IDs leak order volume: the real cost of switching to UUID
Auto-increment IDs expose business volume, but UUIDs bring collision odds and index storage costs. This note covers 122 random bits, birthday-bound collision math, how v4 differs from v1, and how to choose a primary key.