Color Contrast Checker
How it works
The contrast ratio is computed from the WCAG 2.x relative luminance formula for each color, then (lighter + 0.05) / (darker + 0.05) — it ranges from 1 (identical colors) to 21 (pure black on pure white). AA requires at least 4.5:1 for normal text or 3:1 for large text; AAA requires 7:1 or 4.5:1.
"Large text" means 18pt (24px) and up, or 14pt (~18.5px) and up when bold — the WCAG definition used above to pick the right threshold.
Other tools
Color & Design
- Color ConverterConvert colors between HEX, RGB, HSL and CMYK.
- Color Shade GeneratorGenerate a shade and tint ramp from any color.
- CSS Gradient GeneratorBuild linear and radial CSS gradients from color stops.
- Color Palette GeneratorComplementary, triadic and analogous color schemes.
- CSS Box-Shadow GeneratorBuild a CSS box-shadow with a live preview.
- CSS Clamp() Fluid Typography CalculatorA responsive clamp() font-size from a min and max size.
- Color Blindness SimulatorSee how a color looks under common color vision deficiencies.
Text
- Word CounterLive word, character and reading-time stats.
- Case ConverterUPPER, lower, Title, camelCase, snake_case and more.
- Lorem Ipsum GeneratorPlaceholder text by words, sentences or paragraphs.
- Diff CheckerLine-by-line diff of two text blocks via LCS.
- Text CleanerTrim, collapse blanks, dedupe and sort lines of text.
- Regex TesterTest JavaScript regular expressions against your own text — matches, indices and capture groups.
- Markdown PreviewerLive preview of a small Markdown subset — headings, bold, italic, code, links and lists.
- Slug GeneratorTurn any text into a lowercase, URL-safe slug — accents stripped, punctuation collapsed.
- Unicode Code Point InspectorPer-character code point, U+ hex value and UTF-8 byte length, including emoji outside the BMP.
- Word Frequency AnalyzerCase-insensitive word counts, ranked most to least common.
- Regex Cheat SheetBrowsable reference of common regex patterns and syntax.
- Readability Score CalculatorFlesch-Kincaid reading ease and grade level of your text.
- Text Truncator / Excerpt GeneratorTruncate text to a length at a word boundary, with an ellipsis.
- Find and Replace (Regex)Replace every regex match in text with a replacement pattern.
Code & data
- JSON FormatterPretty-print, minify and validate JSON.
- Base64 Encoder / DecoderEncode or decode Base64 with Unicode support.
- XML FormatterPretty-print and validate XML, with clear errors on mismatched tags.
- JSON Path EvaluatorPull a value out of JSON with a simple dot/bracket path.
- CSS Beautifier / MinifierBeautify or minify CSS — string- and comment-aware.
- SQL FormatterBeautify SQL by keyword — SELECT, FROM, WHERE, JOIN and more.
- HTML FormatterIndent nested HTML tags, with void elements handled correctly.
- YAML ⇄ JSON ConverterConvert YAML to JSON or JSON back to YAML.
- SVG Formatter / MinifierPretty-print or minify SVG markup.
- JSON to TypeScript ConverterGenerate a TypeScript interface from a JSON sample.
- JSON Diff CheckerStructural differences between two JSON documents.
- INI / Properties File ParserConvert INI or .properties key=value files to JSON and back.
- GraphQL Query FormatterPretty-print a GraphQL query or mutation.
- .env File ParserConvert a .env file to JSON and back, comments and quotes intact.
- CSV Diff CheckerRow-by-row and cell-by-cell differences between two CSV files.
Encoding
- URL Encoder / DecoderPercent-encode or decode URLs and query strings.
- HTML Entity Encoder / DecoderEscape or unescape HTML entities like & and <.
- Base32 Encoder / DecoderEncode or decode RFC 4648 Base32 text.
- Hex ⇄ Text ConverterConvert text to hexadecimal bytes and back.
- Binary ⇄ Text ConverterConvert text to binary bytes and back.
- CSV ⇄ JSON ConverterConvert CSV to JSON or JSON back to CSV, with proper quoted-field handling.
- Query String Parser & BuilderSplit a query string into key/value pairs, or build one from pairs.
- String Escape / UnescapeEscape or unescape strings for JSON/JS literals or regex patterns.
- Punycode / IDN ConverterConvert a domain name between Unicode and Punycode.
- File to Base64 ConverterConvert any local file to a Base64 data URI.
- ROT13 / Caesar CipherShift letters by any amount — ROT13 and beyond.
- Morse Code TranslatorConvert text to Morse code and back.
- Base58 Encoder / DecoderEncode or decode Base58, the Bitcoin-address alphabet.
Hashing & Security
- Hash GeneratorGenerate SHA-1, SHA-256, SHA-384 and SHA-512 hashes.
- HMAC GeneratorGenerate keyed HMAC signatures with SHA-256/384/512.
- JWT DecoderDecode a JWT header and payload — no signature verification.
- Password Strength CheckerEstimate password entropy and flag common weaknesses.
- Credit Card Number ValidatorCheck a card number against the Luhn checksum.
- IBAN ValidatorCheck an IBAN's shape and mod-97 checksum.
- JWT EncoderBuild and sign a JWT with a header and payload.
- Basic Auth Header Encoder / DecoderBuild or decode an HTTP Basic Authorization header.
- CRC32 Checksum CalculatorCompute the CRC32 checksum of text or a file.
- Password Policy CheckerCheck a password against configurable length and character rules.
Web & Network
- URL ParserBreak a URL into protocol, host, port, path, query and hash.
- User-Agent ParserBest-effort browser, OS and device type from a UA string.
- HTTP Status Code ReferenceBrowsable table of HTTP status codes with lookup.
- CIDR / Subnet CalculatorNetwork, broadcast, mask and usable host range from CIDR.
- IP Address ConverterConvert IPv4 between decimal, integer, binary and hex.
- MAC Address FormatterReformat a MAC address between colon, dash, dot and none.
- HTTP Header ParserParse raw HTTP headers into a readable table.
- Sitemap ValidatorCheck an XML sitemap against the sitemap protocol.
- DNS Record Type ReferenceBrowsable reference of DNS record types and what each is for.
- User-Agent String BuilderBuild a realistic User-Agent string from browser, OS and device.
- MIME Type LookupLook up the MIME type for a file extension, or the reverse.
Numbers & CS
- Bitwise Operations CalculatorAND, OR, XOR, NOT, and bit shifts with binary display.
- Two's Complement CalculatorConvert signed integers to two's complement binary and back.
- IEEE 754 Float ConverterConvert decimals to IEEE 754 single/double-precision bits and back.
- ASCII Table ReferenceFull 7-bit ASCII table with character, hex, and control-code lookup.
- Levenshtein Distance CalculatorEdit distance and similarity percentage between two strings.
- Number FormatterAdd thousands separators or convert number formats.
- Prime Number CheckerCheck primality and list prime factors.
- GCD / LCM CalculatorGreatest common divisor and least common multiple.
- Big-O Complexity ReferenceBrowsable reference of common time-complexity classes.
- Matrix CalculatorAdd, multiply or find the determinant of small matrices.
- Combinatorics CalculatorPermutations (nPr) and combinations (nCr) of n items.
Date & Time
- Timestamp / Epoch ConverterConvert Unix epoch seconds or milliseconds to a date, or a date to an epoch value.
- Date Format ConverterReformat a date using YYYY, MM, DD, HH, mm, ss tokens — always in UTC.
- ISO 8601 Duration ParserParse a PnYnMnDTnHnMnS duration into years, months, days, hours, minutes and seconds.
- Cron Expression Parser & ExplainerParse a 5-field cron expression into plain English and see its next run times.
- Date Add / Subtract CalculatorAdd or subtract days, months or years from a date.
- Business Days CalculatorWeekdays between two dates, weekends excluded.
- Meeting Time Overlap FinderOverlapping working hours across two or more time zones.
- Relative Time FormatterFormat a timestamp as "3 hours ago" or "in 2 days".
Generators
- UUID / GUID GeneratorRandom version-4 UUIDs, or the fixed nil UUID.
- ULID GeneratorSortable, timestamp-prefixed unique IDs.
- Random String / Token GeneratorAlphanumeric, hex, base64url or numeric tokens of any length.
- Meta Tag & Open Graph GeneratorTitle, description, Open Graph and Twitter Card tags.
- Fake Data GeneratorMock rows of names, emails, phone numbers and IDs.
- Placeholder Image GeneratorAn SVG placeholder image at any size, as a data URI.
- Cron Expression BuilderBuild a cron expression from a simple schedule.
- Markdown Table GeneratorTurn pasted CSV or tab-delimited data into a Markdown table.
- .gitignore GeneratorAssemble a .gitignore from common language and editor templates.
- License Text GeneratorFull open-source license text — MIT, Apache-2.0, GPL-3.0 and more.