Free, client-side

Tools

Twenty-three browser-based utilities. Every one runs entirely in your browser: nothing is uploaded, nothing is logged, nothing is stored.

These exist because the ad-supported equivalents that outrank them in search all upload your data to somebody's server to do work your browser can do on its own. That is a choice about who the tool is for.

Converters

CSV ↔ JSONConvert between CSV and JSON in either direction Markdown to HTMLClean HTML out of Markdown source Markdown to LaTeXMarkdown source into LaTeX Epoch time converterUnix timestamps to human dates and back URL encoder and decoderPercent-encoding both ways

Formatters and validators

JSON formatter and validatorPretty-print and validate in one pass Markdown previewerLive render as you type Regex tester and debuggerMatch, group and explain a pattern CSV QACheck a CSV for structural problems before you trust it

Prompt engineering

Lexideck prompt engineerStructured prompt construction on the Lexideck method WYSIWYG prompt editorVisual editing with code blocks preserved WYSIWYG Markdown generatorCompose visually, get Markdown out

Developer utilities

UUID generatorGenerate UUIDs in bulk Color contrast checkerTest a pair against WCAG thresholds CalculatorGeneral-purpose calculator IEG scientific calculatorScientific calculator with the IEG constants

Network

WebSocket testerOpen a socket, send frames, watch the traffic Network latencyMeasure round-trip time from the browser

Visual

Dominant colour finderPull the dominant colours out of an image as a usable palette OKLCH palette generatorBuild perceptually even palettes in OKLCH with gamut warnings

Accessibility

A single-pair contrast checker is under developer utilities. These grids do every pair in a palette at once.

WCAG contrast gridEvery foreground and background pair scored against WCAG 2.1 APCA contrast gridThe same grid scored with APCA, the WCAG 3 candidate Colour vision simulatorSee a palette or image as protan, deutan and tritan vision does