Free tools that run in your browser

Format, minify and validate JSON in your browser. Reports the line and column of a syntax error, sorts keys, and never uploads what you paste.

Convert Unix timestamps to dates and back. Handles seconds and milliseconds, shows UTC and local time, and runs entirely in your browser.

Encode text to Base64 and decode it back, with correct UTF-8 handling for Chinese and emoji. URL-safe alphabet supported. Runs in your browser.

Generate MD5, SHA-1, SHA-256, SHA-384 and SHA-512 hashes of text or a file, and compare against a published checksum. Files are never uploaded.

Generate random v4 UUIDs or time-ordered v7 UUIDs in bulk, from your browser. Explains which version to use as a database primary key, and why.

Test a regular expression against your text, see every match highlighted, and read a plain-English breakdown of what each part of the pattern does.

Every common package-manager task side by side across npm, Yarn, pnpm and Bun, with your package name filled in. Marks where Yarn 1 differs and where there is no equivalent.

The npm command you know beside its Yarn equivalent, for every common task. Covers both Yarn 1 (Classic) and Yarn 2+ (Berry), which differ on most of the interesting ones.

The npm command you know beside its pnpm equivalent, for every common task — plus what changes when node_modules stops being flat.

Reads the first bytes of a file in your browser and tells you the actual format, not the one the extension claims. Includes a reference table of magic numbers.

Generate a private key and a certificate signing request with WebCrypto, in this tab. Nothing is uploaded, because there is no server on this page to upload it to.

Every HTTP status code, grouped by class, with the distinctions that actually matter: 301 against 308, 401 against 403, 502 against 504.

What a 404 actually means, why it is not the same as 410, and what to check when you get one you did not expect.

What a 301 redirect means, how it differs from 302, 307 and 308, and why a redirected POST can arrive as a GET.

What a 502 means, how it differs from 503 and 504, and what to check when your own server returns one.

Percent-encode text for a URL in your browser, showing encodeURIComponent and encodeURI side by side so you can pick the right one.

Decode percent-encoded URLs and query strings in your browser, with a clear message when an escape is malformed.

Escape HTML special characters in your browser, with a choice between the minimum HTML requires and full numeric escaping.

Decode HTML entities — named, decimal and hexadecimal — back to plain text in your browser.

Convert text to \u escape sequences and back in your browser, with correct handling of characters above U+FFFF.

Convert between number bases in your browser with arbitrary precision, so 64-bit values are exact rather than silently rounded.

Convert hexadecimal to decimal in your browser with arbitrary precision, so 64-bit hex values convert exactly.

Convert binary to decimal in your browser with arbitrary precision, and see the signed reading at each register width.

Convert hex bytes to text and back in your browser, choosing the character encoding rather than having it guessed.

Convert internationalised domain names to and from Punycode in your browser, and see when a domain mixes scripts to impersonate another.

Decode a JSON Web Token in your browser. The token never leaves the tab, which matters because a JWT is usually a live session.

Generate strong random passwords in your browser using the platform CSPRNG, with entropy reported in bits rather than a coloured bar.

Check how strong a password is, measured in bits of entropy, entirely in your browser. Nothing is transmitted or stored.

Parse a cron expression in your browser, explain each field, and see the next runs in a real time zone — including the ones daylight saving removes.

Compare two texts line by line and see exactly what was added and removed. Ignore case or whitespace, and hide unchanged lines. Runs in your browser.

Count words, characters, sentences and paragraphs, with correct counting for Chinese, Japanese and Korean text and for emoji. Runs in your browser.

Convert whole numbers into Roman numerals, Chinese capital numerals (大寫) and Suzhou numerals, in your browser.

Convert numbers to Roman numerals and back in your browser, using the subtractive form, with the 3999 limit explained rather than fudged.

Convert an amount into Chinese capital numerals for a cheque, with the zero, tens and 整 rules applied properly rather than by substitution.

Convert numbers to Suzhou numerals in your browser, including the alternation rule that keeps consecutive strokes readable.

Convert text between naming conventions in your browser. Acronyms stay whole and CJK is left alone.

Sort, deduplicate and shuffle lines of text in your browser, with stroke-count and pinyin collation for Chinese.

Translate text to Morse code and back in your browser, and hear it at any speed with correct timing ratios.

Generate lorem ipsum placeholder text in your browser, by paragraph and sentence count.

Generate Chinese placeholder text that sets like real Chinese, drawn from common characters rather than random code points.

Convert between Simplified and Traditional Chinese, with Taiwan and Hong Kong variants and optional regional vocabulary. Runs entirely in your browser.

Arrows, maths, currency, punctuation, keyboard and kaomoji symbols. Click any character to copy it — no install, nothing uploaded.

Full-width and half-width punctuation for Chinese and Japanese text. Which to use, why mixing them looks wrong, and how the quotation conventions differ.

Japanese-style horizontal emoticons to copy. What kaomoji are, why they read upright, and how they differ from emoji.

Paste a script and read it to camera at a pace set in words per minute. Full screen, mirror mode for beam-splitter rigs, and a live estimate of how long it runs.

Convert images between PNG, JPG, WebP and AVIF in your browser. Batch conversion, quality control, and nothing is ever uploaded.

Convert iPhone HEIC photos to JPG in your browser. Batch conversion, adjustable quality, and your photos are never uploaded to a server.

Shrink JPG, PNG and WebP images in your browser. Adjust quality, resize the longest edge, and see exactly how much each file saved.

Split an image into equal pieces and download them as a zip. Runs in your browser, so the picture is never uploaded.

Read the EXIF metadata in a photo — JPEG, HEIC, AVIF, PNG, WebP or TIFF — including GPS coordinates, and strip it losslessly. Nothing is uploaded.

Combine two to nine photos into one image, in your browser. The collage is sized from your best photo, not your worst.

Crop a photo to a circle and add a coloured frame, in your browser. Exports a transparent PNG at up to 1024 px.

Make a QR code from a URL or any text and download it as a PNG or a print-ready SVG. Generated in your browser, with no tracking redirect.

Turn a network name and password into a QR code guests can scan to join, with no app and no typing. Built in your browser — the password is never sent anywhere.

Read a QR code from a photo or your camera, in your browser. The link is shown, never opened.

Generate a complete favicon set in your browser: a multi-size .ico, the PNGs, the manifest and the markup.

Combine several PDFs into one, in the order you choose, without uploading anything. The merge happens in your browser.

Split a PDF by page range, into single pages, or every N pages, entirely in your browser.

Turn images into a PDF in your browser, with the effective print resolution reported for each page.

Rename every file in a folder from a pattern, in Chrome or Edge. The files never leave your disk, and collisions are caught before anything is written.

Convert subtitles between SRT, WebVTT and ASS/SSA, and shift the whole timeline when they are out of sync. Runs in your browser; says what each format cannot carry.

Convert an SRT subtitle file to WebVTT so an HTML <video> will actually show it. Runs in your browser. Covers the header, the comma, the MIME type and the encoding.

Convert ASS or SSA subtitles to SRT so a TV, set-top box or older player can read them. Runs in your browser, and lists exactly what the styling loses on the way.

Work out an exact age in years, months and days from a date of birth, plus total days and weeks and the time until the next birthday.

Work out your body mass index and see it against the WHO, WHO Asia-Pacific and Taiwanese thresholds — which classify the same number differently.

Convert your cat’s age to human-equivalent years. The first year counts for fifteen, the second for nine, and every year after for four.

Convert your dog’s age to human years using the veterinary table, with the size adjustment — and the 2020 epigenetic formula that disagrees with it.

Count the days, weeks, months and business days between two dates. Includes the inclusive-versus-exclusive trap that causes off-by-one errors.

Work out the date a number of days, weeks, months or years from a start date — with correct month-end handling.

Convert shoe sizes between US, UK, EU and centimetres, for men’s and women’s sizing — and why measuring your foot beats every chart.

A printable multiplication chart to 9×9, 12×12 or 20×20, with the patterns worth noticing and why the size differs between countries.

Every standard paper size in millimetres and inches, including the R-number photo sizes used in Taiwan and Hong Kong.

Which plug and what voltage, by country. Most modern chargers handle the voltage, so the plug is usually the only real problem.

International dialling codes by country, with the trunk prefix that has to be dropped when calling from abroad.

Decode resistor colour bands into a value, and turn a value back into bands, with the E-series limits made explicit.

Build a relationship chain and get the correct Chinese kinship term. The five words for "uncle", the 堂/表 cousin split, and where Hong Kong differs.

Convert any date between the Gregorian and Chinese lunisolar calendars, 1900–2100, with the stem-branch year, zodiac animal and solar term. Computed from astronomy, not guessed.

Enter the lunar date you keep and see the Gregorian date it falls on for the next fifteen years. Explains the eleven-day drift and what happens to a leap-month birthday.

Every 節氣 for a chosen year, with its date, weekday and the Sun's ecliptic longitude. Explains why 清明 is always 4–6 April, and which twelve terms decide the leap month.

Your 生肖 from your date of birth, using the actual Lunar New Year boundary rather than 1 January. Shows the stem-branch year, the element, and the 立春 convention where it disagrees.

Convert between metric and imperial units for length, weight, temperature, area, volume, speed, data and time. Runs in your browser.

See the public IP address, network and approximate location that servers see when you connect, plus what your browser reveals about itself.

Measure your download speed, upload speed, latency and jitter, then see how your connection compares with other tests from your provider and your country.

Expand bit.ly, t.co, tinyurl and other short links to see the full destination, and every redirect in between, without opening them.

Check whether a website favicon meets Google Search requirements: square, at least 8×8px, declared with a supported rel, and crawlable by Googlebot-Image.

Check a page’s Open Graph and Twitter card tags, see the real preview image, and find out why a link shares without a picture.

Open a WebSocket from your browser, send frames and read what comes back. Connects straight to your server, so localhost works. Explains close code 1006 rather than printing it.

Your screen resolution in device and CSS pixels, viewport size, pixel ratio, refresh rate and colour depth — read live in your browser.

Fill the screen with solid colours to find dead and stuck pixels, backlight bleed and uniformity problems. Runs in your browser.

Press a key and see its event.key, event.code and keyCode. Test a keyboard for dead or repeating keys, and learn which property to bind a shortcut to.

Test your webcam and microphone in the browser. Nothing is recorded and nothing is uploaded — this page has no server to send it to.

Your browser, engine, operating system and user-agent string, plus what the browser can actually do. Why the string is a guess and features are not.

Generate printable grid and graph paper at any square size, on A4, A5, B5 or Letter. The squares come out the size you asked for.

Generate printable Chinese composition paper — 400 or 300 character cells, optional centre gutter, on A4, A5 or B5. Cells are sized from the character count.

Convert a colour between every common format at once, in your browser, with the CMYK caveat stated rather than hidden.

Convert a hex colour code to RGB in your browser, with the shorthand and alpha forms handled.

Convert RGB values to a hex colour code in your browser, in both the old and modern CSS syntaxes.

Convert a hex colour to HSL in your browser, and see why HSL is the format worth editing by hand.

Convert RGB to CMYK in your browser, with an honest account of why the result is an approximation without an ICC profile.

Pick a colour and get every format, a tint-and-shade ramp, and five harmony sets, in your browser.

Check colour contrast against WCAG AA and AAA for normal text, large text and non-text elements, with a suggested fix.

Every CSS named colour with its hex value, sortable by hue and lightness. Click to copy.

Select a precise section of an audio file and export it as MP3 or WAV. Decoding, trimming and encoding stay in your browser.

Arrange and merge audio clips into one MP3 or WAV file. Decoding, joining and encoding happen entirely in your browser.

Convert MP3, M4A, FLAC, Ogg and WAV files to MP3 or WAV without uploading them. Processing stays on your device.

在瀏覽器裡把 M4A 與 AAC 音訊轉成 MP3，特別適合幾乎沒別的軟體打得開的 iPhone 語音備忘錄。

在瀏覽器裡把 WAV 轉成 MP3，檔案通常會縮到原本的十分之一左右。沒有任何上傳。

在瀏覽器裡把 FLAC 轉成 MP3。沒有上傳，你的無損原檔也不會被更動。

在瀏覽器裡把 Ogg Vorbis 與 Opus 音訊轉成 MP3，給讀不懂 Ogg 的播放器用。沒有任何上傳。

在瀏覽器裡把 MP3 轉成未壓縮的 WAV，給讀不懂 MP3 的剪輯軟體用。沒有任何上傳。

Read audio format details, title, artist, album, track numbers and embedded artwork locally from MP3, M4A, FLAC, Ogg and WAV files.

Adjust an audio file to a chosen dBFS sample peak, preview the result, and export WAV or MP3 without uploading the recording.

Run a local metronome with tap tempo, 30–300 BPM, bar accents, meters and beat subdivisions. No account, recording or upload.