CapyToolkit

CapyToolkit is a free reference library that happens to contain 45+ working tools. The catalog spans nine categories: hardware and display diagnostics, developer parsers and encoders, security and privacy tools, audio and acoustic testing, math and engineering calculators, text analysis, web design utilities, network references, and personal tools.

Each tool page pairs the utility with example-driven reference content: the resistor calculator explains band tolerance, the subnet calculator breaks down CIDR notation, the MIME and HTTP status references are searchable, and the contrast checker quotes WCAG AA and AAA thresholds. Personal tools include a passport photo cropper, image shrinker, PDF toolkit, phone-scan deskew, and receipt splitter.

Everything runs client-side in the browser. Files never upload, text never leaves the tab, and no account is required. The site installs as an app, works offline, and is also on the Microsoft Store for Windows. New tools ship regularly.