15 free tools · run in your browser
Free web developer tools
Quick utilities for the small jobs that interrupt real work: formatting JSON, testing a pattern, checking a cron schedule or picking accessible colors. They run in your browser, with no sign-up.
Web developer tools
- JSON to YAML converterConvert YAML and JSON, test regex, build cron schedules and validate .env files.
- JSON formatterFormat, minify, validate, convert YAML and inspect object paths locally.
- JSON diffCompare two JSON or YAML documents by structure, see added, removed and changed keys by path, and merge them into one with your choice of winner.
- JSON to CSVConvert JSON to CSV with nested fields flattened, arrays handled, columns chosen and a spreadsheet-safe download.
- Remove duplicates from CSVRemove duplicate and empty rows from a CSV by chosen columns, keeping IDs and dates exactly as they are.
- Regex testerTest JavaScript patterns with highlights, capture groups and a replacement preview.
- Cron expression generatorBuild five-field cron schedules and preview the next ten runs in a timezone.
- Base64 decodeEncode UTF-8 text or files, decode Base64, and generate file checksums.
- UUID generatorGenerate cryptographically random version 4 UUIDs individually or in bulk.
- Epoch converterConvert seconds, milliseconds, or timezone-qualified dates in batches.
- Meta tag generatorGenerate escaped HTML metadata, canonical, Open Graph and Twitter tags.
- CSS gradient generatorCreate linear or radial gradients with color stops, opacity, CSS and PNG export.
- Color contrast checkerCheck colour contrast against WCAG 2.2 AA and AAA for text and UI, with transparency and passing colour suggestions.
- Color palette generatorGenerate colour palettes, lock colours you like, extract palettes from images and export CSS, Tailwind or JSON.
- Font pairingPreview Google Font pairings for headings and body text, adjust sizes and export the CSS and link tags.
Which tool do you need?
- Pretty-print or validate a JSON payload, or turn it into YAML: JSON Formatter & Validator.
- See exactly what changed between two configs or API responses: JSON & YAML Diff and Merge.
- Get an API response into a spreadsheet: JSON to CSV Converter, then CSV Cleaner to drop duplicate rows.
- Debug a regular expression with capture groups and a replace preview: Regex Tester.
- Check when a cron job will really run, in any time zone: Cron Expression Generator.
- Decode a Base64 string or hash a value with SHA-256: Base64 & Hash Tool.
- Read a timestamp from a log: Epoch Converter. Need IDs for test data: UUID Generator.
- Ship a page: Meta Tag Generator for Open Graph tags, Color Contrast Checker for WCAG, plus the palette, gradient and font pairing tools.
Your data stays on your machine
Pasting a production token or a customer record into a random website is a real risk. These tools do their work in JavaScript in your browser tab: the JSON you format, the strings you decode and the patterns you test are not uploaded or stored. There is no account and nothing to install.
One exception worth knowing: the font pairing tool loads font files from Google Fonts to show the previews. Your own input still isn't sent anywhere.
Small details that save debugging time
The tools are built around the mistakes developers actually make. The cron generator shows the next ten runs in the zone your scheduler uses, including what happens on daylight saving days, and flags the rule that day-of-month and day-of-week are combined with OR. The regex tester uses the JavaScript engine, so what matches here matches in your browser or Node code. The CSV tools keep IDs and dates as text, so leading zeros and long numbers survive. The contrast checker tests against WCAG 2.2 AA and AAA and suggests passing colors.
For worked examples, see cron expression examples.
Guides
Frequently asked questions
Are these developer tools free?+
Yes. Every tool is free to use with no account, no sign-up and no usage limit.
Is it safe to paste API keys or JSON with personal data?+
The processing happens in your browser and the input isn't uploaded or saved. As a general habit, still rotate any secret you've pasted somewhere you didn't intend to.
Which regex flavor does the regex tester use?+
JavaScript (ECMAScript), as run by your browser. Most everyday syntax is shared with PCRE and Python, but features like lookbehind support and named-group syntax can differ, so test in the flavor you deploy.
Does the cron generator support seconds or Quartz syntax?+
No. It checks standard five-field Unix cron. Six- or seven-field Quartz expressions and macros like @daily are rejected; write @daily as 0 0 * * *.
What's the difference between Base64 and hashing?+
Base64 is a reversible encoding: anyone can decode it, so it isn't encryption. A hash such as SHA-256 is one-way: you can't get the input back, which is why hashes are used for checksums and comparing values.
Are generated UUIDs unique?+
Version 4 UUIDs are 122 random bits from your browser's cryptographic random generator, so the chance of a collision is negligible for practical purposes.
Which contrast ratio do I need for WCAG AA?+
4.5:1 for normal body text and 3:1 for large text (about 24px, or 19px bold) and for UI components and graphics. AAA asks for 7:1 for normal text.