Checkers & Developer

Validate IBAN and EAN, format and check JSON, test regex, look up DNS, see your IP and screen resolution – fast checking tools right in your browser.

An IBAN validator (ISO 13616 check digits, bank name for German accounts), EU VAT number format checker, EAN, ISBN and Luhn checkers, email syntax checker, JSON formatter, XML/CSV validator, regex tester, Base64 and URL encoder, hash and UUID generator, Unix timestamp converter, DNS lookup, user agent, screen resolution and what is my IP; for web design a box shadow, border radius and CSS gradient generator, an aspect ratio calculator and font pairings from system fonts. Your input stays in your browser.

54 tools

Most used

What is my IP address?What is my IP? See your public IPv4 or IPv6 address at once, plus approximate location, internet provider and browser details. Free, never stored.
IPv4 Subnet Calculator: Network, Broadcast, Host Range and SubnettingIPv4 subnet calculator with CIDR: network address, broadcast, usable host range, subnet mask, wildcard and host count – binary working and subnetting.
ASCII table with decimal, hex, octal, binary and Unicode lookupASCII table 0–127 plus Latin-1 and Windows-1252: decimal, hex, octal, binary, HTML entity, control codes. Search it, click to copy, convert text to codes.
DNS lookupDNS lookup for any domain: A, AAAA, MX, TXT, CNAME, NS, SOA, CAA, SRV and PTR, all at once if you like, plus an SPF, DMARC and DKIM check in plain words.
XML formatterXML formatter: beautify, minify and validate with line and column of the error, tree view, XPath query and XML to JSON. In your browser, no upload.
JWT decoder: read and verify a JSON Web TokenJWT decoder for header, payload and expiry (exp, iat, nbf). Verify the signature with a secret or public key. Everything runs locally in your browser.
JSON compareJSON compare: find the differences between two JSON documents with path, old and new value. Key order is ignored. In your browser, no upload.
UUID generator: create and validate UUID v4 and v7Generate UUIDs online: version 4 (random) or version 7 (time-ordered), up to 1,000 at once. Validate a UUID and decode its version, variant and timestamp.

All tools

SQL formatter (format SQL online)SQL formatter for readable queries: uppercase keywords, indentation, columns and conditions on separate lines. Also minifies SQL. Runs locally in your browser.
IBAN CheckerValidate any IBAN: mod-97 check digits, length and structure for 89 countries, plus bank and BIC for German IBANs. Runs in your browser – nothing is sent.
Regex TesterTest JavaScript regular expressions live: matches highlighted, capture groups in a table, every part of the pattern explained. Free, nothing uploaded.
HTML formatterHTML formatter: indent source code to make it readable, or minify it to a single line, with warnings about unclosed tags. Runs locally in your browser.
HTTP Status CodesLook up HTTP status codes: the meaning of 200, 301, 404, 500 and over 40 more codes explained, with search by code or keyword and a filter by class.
Hash Generator: SHA-256, SHA-512, SHA-1, MD5Calculate SHA-256, SHA-384, SHA-512, SHA-1 and MD5 hashes of text or files and verify checksums – locally in your browser, no upload, free.
Aspect Ratio CalculatorCalculate the aspect ratio from width and height (1920 × 1080 = 16:9), find the missing side, decimal value, nearest standard ratio and CSS aspect-ratio.
What is my screen resolution?Instantly see your screen resolution, physical pixels, browser viewport, devicePixelRatio, aspect ratio and CSS breakpoint. Live, right in your browser.
Unix timestamp converterConvert a Unix timestamp to a date and back. Seconds, milliseconds, micro- and nanoseconds detected automatically; UTC, local time, ISO 8601 and more.
Cron expression generator and explainerCron expression generator and explainer: build or paste an expression, read it in plain words and see the next run times. Unix cron, Spring and Quartz, local.
Chmod CalculatorChmod calculator: tick the permissions or type 755, rwxr-xr-x or u=rwx and see every notation at once, plus the command to copy. Free, runs in your browser.
What is my user agent?See your user agent string and detect browser, version, engine, OS and device type, plus User-Agent Client Hints. Parse any other UA too. Runs locally.
YAML to JSON converter (and JSON to YAML)YAML to JSON converter and JSON to YAML following YAML 1.2: lists, anchors, text blocks, comments. Errors show the line number. Runs in your browser, no upload.
Markdown to HTML converter: preview, HTML code, downloadMarkdown to HTML converter with live preview: headings, lists, tables and code following CommonMark. Clean HTML code to copy, safe with no scripts. Free.
Redirect Checker: Trace the Full Redirect ChainThis redirect checker traces every hop of a URL with its status code (301, 302, 307, 308), target and timing – and flags chains, loops and HTTPS mistakes.
Markdown table generatorMarkdown table generator: paste data from Excel, Google Sheets or CSV and copy it as an aligned Markdown, HTML or LaTeX table – locally in your browser.
Screen size calculatorScreen size calculator: width and height in cm and inches from the diagonal and aspect ratio, plus pixel density (ppi), pixel size and the distance pixels blur.
Text to binary converter (and binary to text)Convert text to binary, hex, decimal or octal and translate binary back to text – with UTF-8 for accents and emoji, right in your browser, nothing uploaded.
Font pairing – heading and body font combinationsFont pairs for headings and body text with live preview, copy-ready CSS and availability on Windows, Mac, iPhone and Android – system fonts only, no web fonts.
IEEE 754 converterIEEE 754 converter for half, single and double: convert decimal, hex or bits, and see sign, exponent, mantissa and the exact stored value with rounding error.
CSS gradient generatorBuild CSS gradients: linear, radial or conic, as many color stops as you need, angle and fallback color – live preview and CSS ready to copy.
Px to Rem ConverterPx to rem converter with your own base font size, plus em, pt, percent and vw, and a lookup table of common font sizes. Free, no sign-up, works offline.
CSV to JSON converter (and JSON to CSV)Convert CSV to JSON or JSON to CSV online: delimiter auto-detected, numbers and booleans typed, quoted fields handled. Runs in your browser, nothing uploaded.
Base64 Encode and DecodeEncode and decode Base64 and Base64url with proper UTF-8, plus URL encode/decode (percent-encoding). Clear error messages, runs locally in your browser.
Validate Email Address SyntaxCheck one or many email addresses for correct syntax under RFC 5321/5322: lengths, domain labels, international domains (Punycode). Local, nothing sent.
JSON to TypeScript converterConvert JSON to TypeScript: generate types, interfaces or JSON Schema from sample data, with optional fields. Runs in your browser, no upload.
JSON formatter, validator and minifierValidate JSON against RFC 8259 with the exact line, column and a plain-English explanation. Beautify or minify, sort keys, copy. Runs locally in your browser.
CSV to SQL converterConvert CSV to SQL: generate CREATE TABLE and INSERT statements for MySQL, PostgreSQL, SQLite or SQL Server. Types detected, in your browser, no upload.
JavaScript minifierJavaScript minifier: remove comments and whitespace, shrink the code and see the saving in bytes. In your browser, no upload.
CSS minifier: minify, format and inline CSS into HTMLCSS minifier and formatter, plus a CSS inliner for HTML email: safe transformations, errors with line numbers, all in your browser with no upload. Free.
EU VAT Number Checker (Format and Check Digit)Check the format and check digit of an EU VAT number for all 27 member states and Northern Ireland (XI). Runs locally, with links to VIES for validation.
Syntax HighlighterSyntax highlighter online: paste code, pick colors for JavaScript, JSON, HTML, CSS, SQL, Python or Bash and copy highlighted HTML for a blog, email or Word.
CSS box shadow generatorBuild CSS box shadows with sliders: multiple layers, offset, blur, spread, color with alpha, inset and presets – live preview and one-click copy of the CSS.
CSS border radius generatorRound corners with sliders: all corners linked or each on its own, px or %, elliptical 8-value syntax – shortest CSS shorthand, live preview and copy button.
CSS clamp calculatorCSS clamp calculator for fluid font sizes and spacing: enter minimum and maximum values plus the viewport range and copy the finished clamp() value.
EAN and ISBN check digit calculator and validator (GTIN)Validate EAN-8, EAN-13, UPC-A, GTIN-14 and ISBN-10/13 check digits, calculate a missing check digit and convert ISBN-10 to ISBN-13 – free, in your browser.
htaccess redirect generator (301, HTTPS, www).htaccess redirect generator: 301 redirects, force HTTPS, www, domain moves and more. With a URL test run and the Nginx equivalent, local in your browser.
HTML Entities Encode and DecodeHTML entities encode and decode: convert special characters into entities or back into text, named, decimal or hexadecimal, locally in your browser.
HTTP Header Checker with Security GradeSee every HTTP response header of a URL and grade its security headers – HSTS, Content-Security-Policy, X-Frame-Options, Referrer-Policy – from A to F.
JSON Escape / UnescapeJSON escape and unescape online: turn any text into a valid JSON string with escaped quotes, backslashes and line breaks, or decode it back – in your browser.
JSON-LD GeneratorJSON-LD generator for Schema.org: fill in an article, FAQ, product, local business or organization and copy ready-to-use code with a built-in error check.
Luhn algorithm checker: validate and calculate check digitsValidate numbers with the Luhn algorithm (mod 10, ISO/IEC 7812-1) or calculate the check digit – format check only, runs locally in your browser.
robots.txt Checker with Sitemap ValidationIs a URL blocked for Googlebot, Bingbot or AI crawlers? This robots.txt checker shows the deciding rule, flags syntax issues and validates the sitemap.
robots.txt Generatorrobots.txt generator: pick a preset, block or allow paths, add your sitemap and exclude AI crawlers – get a ready-to-copy file with a check for common mistakes.
Sitemap XML generator: build sitemap.xml from your URL listSitemap XML generator without signup: paste URLs, get a valid sitemap.xml per the Sitemaps protocol, check for errors and download it. Runs in your browser.
XML and CSV validator onlineCheck XML for well-formedness and validate CSV against RFC 4180: errors with line and column, auto-detected delimiter, table preview. Runs locally.