Free Developer & SEO Tools — Format, Encode, Test & Optimise

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32 free tools · No sign-up · Last Updated: October 2026

Color PickerPick colours and convert between HEX, RGB and HSL; screen eyedropper in supported browsers. JSON FormatterBeautify, minify and validate JSON with 2- or 4-space indentation; copy or download. UUID GeneratorBulk RFC 9562 UUIDs (v4 random, v7 time-ordered, nil) from crypto.getRandomValues/randomUUID, with uppercase, no-hyphen, braces, JSON and SQL formats, plus a validator showing version, variant and timestamp. Hash GeneratorMD5 (own RFC 1321 code) and SHA-1/256/384/512 (Web Crypto) for UTF-8 text or local files up to 500 MB, hex or Base64, HMAC for SHA, and a checksum comparer. URL Encoder / DecoderPercent-encodes as a URL component (strict RFC 3986), a full URL or form data (+ for spaces); decodes with clear errors; breaks URLs into protocol, host, port, path, decoded query parameters and fragment. HTML Entity Encoder / DecoderEscapes & < > " ' (or also common named entities, or every non-ASCII character as decimal/hex references, emoji-safe) and decodes any named or numeric entity with DOMParser. JWT DecoderDecodes JWT header and payload (Base64URL, UTF-8), pretty-prints JSON, explains registered claims, converts exp/iat/nbf to dates with expiry status, warns on alg none, and optionally verifies HS256/384/512 signatures. Regex TesterLive JavaScript regex testing with g/i/m/s/u/y flags, highlighted matches, match table with numbered and named groups, replacement preview, copy as JS, cheat sheet, and a Web Worker time limit against catastrophic backtracking. JSON to CSV ConverterJSON array → CSV (union of keys, dot-flattened nested objects, arrays as JSON, RFC 4180 quoting) and CSV/TSV → JSON (header row, optional number/boolean typing), comma/semicolon/tab/pipe delimiters, preview table, Excel BOM, file open and download; PapaParse (MIT). CSS / JS / HTML MinifierCSS minifier (own, string/url/calc-safe, keeps /*! licences), JS minifier with Terser 5 (compress + optional mangle, lazy ~1 MB), conservative HTML minifier (pre/textarea/script/style untouched, inline CSS optional), byte savings, file open and download. Unix Timestamp ConverterLive current epoch; timestamp (auto-detected s/ms/µs/ns) to UTC, any IANA zone, ISO 8601 (with offset), RFC 2822 and relative time; date/time in any zone to epoch seconds and ms (DST-aware). Meta Tag GeneratorGenerates charset, viewport, title, description, robots, canonical, theme-color, Open Graph and Twitter/X card tags with escaping, character counters, practical length tips and a Google-style result preview. Robots.txt GeneratorPresets (allow all, block AI training, block all AI, WordPress, block all), disallow/allow paths, sitemap, optional crawl-delay, and per-bot blocking for 14 known AI crawlers from OpenAI, Google, Anthropic, Perplexity, Common Crawl, Apple, Meta, ByteDance and Amazon. Open Graph PreviewParses pasted head HTML with DOMParser and previews link cards for Facebook, X, LinkedIn and WhatsApp using og:/twitter: tags with fallbacks; checks title/description length, image presence, https, loadability, size and 1.91:1 ratio. UTM BuilderAdds utm_source/medium/campaign/content/term/id to a URL with the URL API (existing parameters and fragments kept, old utm values replaced), lowercase normalisation, presets, validation, test link and a downloadable QR code. Color Palette GeneratorHarmony palettes (random, analogous, complementary, triadic, split, mono) with lockable swatches and optional base colour, or k-means++ colour extraction from images on-device; HEX/RGB/HSL, WCAG contrast vs white/black, CSS/Tailwind/JSON/PNG export. CSS Gradient GeneratorVisual gradient builder for linear (angle), radial (circle/ellipse, centre) and conic (start angle, centre) gradients with 2–8 colour stops, presets, random and reverse; outputs CSS with a solid fallback and a 1920×1080 PNG. Cron Expression GeneratorParses standard 5-field cron (lists, ranges, steps, names, 7 = Sunday, @macros), explains it in plain English, lists the next 5 run times in local time using the day-of-month OR day-of-week rule, and builds common schedules. CSV to Excel ConverterBrowser-only CSV to XLSX converter: drop one or many CSV/TSV files or paste text; auto-detects the delimiter (comma, semicolon, tab, pipe); multiple files become sheets of one workbook or separate .xlsx files in a ZIP; plain numbers stored as numbers while leading-zero values, +91 numbers, 16+ digit IDs and dates stay text; preview; column widths set; Unicode kept. Excel to CSV ConverterBrowser-only Excel to CSV converter: reads .xlsx, .xls, .xlsm, .xlsb and .ods (SheetJS); choose a sheet or export all sheets to a ZIP; comma, semicolon, tab or pipe; optional BOM for Excel; values exported as displayed (formula results, formatted dates/numbers); preview; nothing uploaded. CSV to JSON ConverterBrowser-only CSV to JSON converter (PapaParse): file or paste; auto delimiter; output as array of objects, array of arrays, or object keyed by first column; optional typing of numbers and true/false (leading zeros kept as text); dotted headers can build nested objects; skip empty cells; pretty or minified; duplicate headers made unique; copy/download. CSV to XML ConverterBrowser-only CSV to XML converter: file or paste, auto delimiter (PapaParse); configurable root and row element names; columns as child elements or attributes; skip empty cells; pretty print; header names sanitised into valid XML names (spaces/symbols → _, leading digit or 'xml' prefixed with _); &, <, >, quotes escaped and control characters removed; copy/download .xml. JSON to XML ConverterBrowser-only JSON to XML converter: paste or open .json; objects → nested elements; arrays → repeated elements with the parent key (or a chosen item name for top-level arrays); keys starting with @ → attributes and #text → element text (optional); a single top-level object key becomes the root; null → empty element; names sanitised to valid XML; values escaped; pretty print; live error messages for invalid JSON; copy/download. XML to JSON ConverterBrowser-only XML to JSON converter using the browser's DOMParser: paste or open .xml/.rss/.kml/.gpx/.svg; root element kept as top-level key; attributes with chosen prefix (@, _, or none); repeated elements → arrays (optionally forced everywhere a tag repeats); mixed text as #text; CDATA kept; optional number/boolean typing; pretty or minified; parser error line shown for invalid XML; copy/download. XML to CSV ConverterBrowser-only XML to CSV converter (DOMParser + PapaParse): file or paste; auto-detects the record element (the tag repeated most under one parent) or the user picks from a list of repeating tags with counts; flattens each record — attributes as @name columns, nested elements as dotted paths (customer.city), nested attributes as path@attr, repeated children joined with '; '; union of all columns in first-seen order; preview; comma/semicolon/tab/pipe; optional BOM; copy/download. XML to Excel ConverterBrowser-only XML to XLSX converter (DOMParser + SheetJS): paste or drop XML; auto-detects the record element or the user picks a repeating tag; flattens records (attributes → @columns, nested → dotted columns, nested attributes → path@attr, repeats joined with '; '); plain numbers stored as numbers while leading zeros/long IDs stay text; sheet named after the root element; column widths set; preview; download .xlsx. Excel to XML ConverterBrowser-only Excel to XML converter (SheetJS): opens .xlsx, .xls, .xlsm, .xlsb, .ods or .csv; choose a sheet or include all sheets (each as <sheet name=…>); header row gives element/attribute names (sanitised to valid XML); custom root and row names; attributes option; skip empty cells; values as displayed in Excel; escaped; UTF-8 declaration; copy/download. Split CSV FileBrowser-only CSV splitter (PapaParse + JSZip): CSV/TSV up to 200 MB; split by rows per file, into N files of equal size, or one file per distinct value in a chosen column; header row repeated in each part (optional); quoted line breaks handled so rows are never cut; parts listed with row counts before download; max 1,000 parts; optional BOM; all parts in one ZIP. Split Excel FileBrowser-only Excel splitter (SheetJS + JSZip): opens .xlsx, .xls, .xlsm, .xlsb, .ods up to 50 MB; modes — each sheet into its own file, one sheet by rows per file, or one sheet by distinct column value; header row repeated in every part (optional); parts saved as .xlsx (numbers stay numbers, leading zeros kept) or CSV (UTF-8 with BOM); parts listed before download; max 500 parts; values only. Number Base ConverterNumber base (radix) converter: input in decimal, binary, octal, hexadecimal or any base 2–36; outputs binary, octal, decimal, hexadecimal, base 32 and base 36 (radix digits 0–9 then a–z) together; exact BigInt arithmetic with no size limit; negative numbers with a minus sign; recognises 0x, 0b and 0o prefixes; ignores spaces and underscores; validates digits; optional digit grouping and uppercase hex; bit length shown. HEX to RGB ConverterTwo-way colour converter: HEX (3, 4, 6 or 8 digits, with or without #) ⇄ RGB/rgba (numbers, percentages or plain '27 152 224'); also HSL, approximate CMYK (simple formula, not a print profile), a CSS variable line and the decimal value; built-in colour picker; WCAG 2 contrast ratio of white and black text on the colour with AA/AAA grades; copy HEX, RGB or all formats. Base64 Encode / DecodeBase64 encoder and decoder for text: encodes text as UTF-8 then Base64 (RFC 4648), with optional URL-safe Base64url (- and _ , no padding) and 76-character MIME line wrapping; decoding ignores whitespace, accepts missing padding and URL-safe characters, reports invalid characters or wrong length, and detects bytes that are not valid UTF-8 text (binary data); live or button conversion; swap, copy and download; runs locally.

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