All 237+ Free Online Tools

Open a GLTF, GLB, OBJ, STL or FBX model and read what is really in it: distinct vertices and position entries as two different numbers, triangles, whether the surface is closed, and a screenshot with the model on it.

Read a linear or 2D barcode from an image or camera. Verifies the GS1 check digit, corrects a UPC-A that a browser reports as a thirteen-digit EAN-13, and names which decoder answered.

Chord diagrams whose fingerings are found by searching the fretboard, so the notes under the dots really are the chord's. Ten tunings, sixteen qualities, and the notes named on the page.

See an image through the two published models of colour vision deficiency, Machado 2009 and Vienot 1999, computed in linear light where those models are defined, with the colour pairs that stop being distinguishable listed by name.

A layered raster canvas where a stroke lands under the pointer at every zoom, undo really steps back, and the export is the canvas or a named enlargement of it.

Build an animated GIF89a written from the specification and read back before download, so the frame count, the delays, the loop count and the palette size are reported from the finished file rather than from the request.

Mark a picture up with arrows, shapes, text and freehand, in the picture's own pixels: an annotation is the same size in the file whatever the view is zoomed to.

Remove a background with a model or with a colour key that has a real alpha ramp, scored against a corpus whose right answer was chosen rather than found.

Process many images at once with one operation, with every output decoded again and checked against what was asked for, and the whole batch downloaded as one ZIP.

Arrange photos in one of twelve templates whose every cell rectangle, gap, margin and radius is stated in the output's own pixels before anything is drawn.

A tone curve drawn with its level count and clipping reported, per-range gains in stops of light whose three weights sum to exactly one, and a white balance that is a Bradford adaptation on a published locus. The neutral setting is proved to change nothing.

Extract a palette whose every colour is one the image actually contains, with the share of the picture each one covers. Median cut, k-means in CIE Lab or plain frequency, each named.

Compress to a quality or to a file size, with the size shown being the encoded file to the byte and the cost measured on the pixels: SSIM, PSNR, the worst channel and the share of pixels changed.

Whole-pixel crops with the rectangle typed or dragged, checked by decoding the output and comparing it with the pixels that went in. Quarter turns and mirrors are exact permutations, so nothing is clipped.

Compare two images with a perceptual engine (pixelmatch) that ignores anti-aliasing, or an exact byte engine. Groups changes into regions with bounding boxes, reports SSIM, and handles size mismatches with an explicit policy.

Six published edge operators (Sobel, Prewitt, Scharr, Roberts and both Laplacians) plus the real four-stage Canny, each checked against the browser's own feConvolveMatrix and each naming the paper it comes from.

The seven transforms Filter Effects Module 1 defines, computed from its published matrices and checked against the browser's own implementation, plus exposure in real stops and seeded grain.

Convert between the formats a browser can really write, then open the output and name the format its first bytes say it is. AVIF, BMP and GIF are disabled because a canvas returns a PNG for all three.

Count every pixel into 256 bins per channel, with the luminance definition named rather than assumed: Rec. 709, Rec. 601 or CIE L*. Exports the whole table as RFC 4180 CSV.

Remove EXIF, GPS, XMP and IPTC by rewriting the container rather than re-encoding the picture, so the pixels are byte-for-byte identical and the file gets smaller. Selective removal, batch mode and a ZIP.

Read every metadata block a file carries: EXIF from its TIFF structure, IPTC from its IIM records, XMP from its packet and the ICC colour profile from its header, with GPS converted to decimal degrees with the reference letters applied.

A block average or a centre sample, each named and measurably different, with the colour limit producing exactly that many colours and the count read back off the output.

Resize with the filter named (Lanczos, Mitchell, Catmull-Rom, bilinear, box or nearest) and the option to average LIGHT rather than stored bytes, which is worth 1.24 stops on a detailed picture.

Quarter turns and mirrors as exact permutations, checked by decoding the output and comparing it with what went in. A free angle is marked as the resample it is, and the EXIF Orientation tag is read and named.

Read text off a picture with Tesseract, after preparation that measures the type and enlarges it: 8px text went from a 53 percent character error rate to 8. Every word carries a confidence and a box drawn on the picture.

Convert images to ASCII text art with the ramp measured rather than assumed: each glyph is drawn and its ink counted, the character cell is measured in the font used, and brightness is a named definition.

Turn an image into a data URL whose payload is decoded again and compared byte for byte with the file, with the media type taken from the file's own signature rather than its extension and the size cost of embedding stated in full.

Turn one image into a full icon set, including a real multi-size favicon.ico read back from its own bytes before it is offered. Names the resampling filter, states what a square crop discarded, and decodes every PNG again to confirm its size.

Trace a PNG or JPG into real SVG paths, with holes that stay holes and transparency that is not read as black. The page counts the pixels its own vector differs from the picture, and at the exact setting that count is zero.

Enlarge with the filter named and cited, and the alignment measured: six published kernels matching Pillow to within half a level, premultiplied alpha, and an unsharp mask whose colour space is a choice.

Text, image and tiled watermarks whose padding is measured to the ink, whose rotation keeps the mark on the picture, and whose opacity is source-over: the number is the share of the way from the picture to the mark's own colour.

Caption a picture with text that is measured, wrapped and kept inside the frame. The preview canvas is the exported file, pixel for pixel.

Placeholder images described once and drawn two ways, so the preview, the raster and the SVG are the same picture. The label is measured and made to fit, and the quality slider only appears where quality does something.

Scan QR codes from an image or your camera, in this tab. Reads every code in a picture, rescues a faded or transparent one and says which step worked, and parses WiFi, vCard, calendar, geo and payment payloads by their published grammars.

Wrap a screenshot in a real CSS gradient, a real corner radius and a real device frame. The preview is the export drawn smaller by the same function, so what you see is what the file gets.

Pack frames into a sheet with an atlas that names each sprite's own rectangle, or slice a sheet back apart with margin and spacing read off the pixels. The page checks every frame comes back out of the sheet byte for byte.

Optimize and minify SVG files over a real markup tokenizer, then verify the result by drawing both versions and comparing every pixel.

Render SVG to PNG, JPG or WebP at a chosen size, with the size worked out from the file by the rules that define it and checked against the browser's own rendering.

Twelve procedural patterns that tile exactly, verified live with a measured wrap error and a 3 by 3 repeat view. Perlin, fractal, ridged, Voronoi, marble, wood and geometric grids.

Ten-band graphic EQ that draws the real frequency response from the filter coefficients, matching the rendered audio to 0.03 dB. Clip-safe export, transparent bypass, per-band bandwidth control.

Fade in and out with five curve shapes: linear, exponential, logarithmic, S-curve and equal power. The graph, the preview and the exported file all come from the same function.

Convert between MP3, WAV, OGG, AAC, M4A and FLAC with a bitrate, sample rate, channel count and bit depth that all reach the encoder, and a panel that reports what was actually written.

Join clips end to end or stack them on one timeline, with an equal-power crossfade that holds the level through the join, BS.1770 loudness matching between files, and the merged result measured before you download it.

Shift pitch by semitones and cents with WSOLA, keeping the length or changing it like tape speed. Measures its own output and reports the error in cents: a perfect fifth lands within 0.5 cents.

Full-track spectrogram with a calibrated dBFS colour scale, labelled Hz axis, and log or linear frequency. Plus four live modes, microphone input, a peak-frequency and note readout, and PNG or WebM export.

Change tempo from 0.25x to 4x with WSOLA, holding pitch to within half a cent, or let pitch move with it like tape. Measures the output and shows how far the pitch actually went.

Transcribe audio into sheet music in your browser: the Basic Pitch neural network finds the notes in humming, singing, solo instruments, piano or a full song, then the tool tracks the beat through rubato, detects the meter (4/4, 3/4, 6/8, 12/8) and the downbeat, writes triplets and chord symbols, names the key, and engraves the result with tuplets, ties and a metronome mark; a song comes out as a piano arrangement, the tune over its bass line. A piano roll drawn on the tracked beats lets you remove or move notes; every setting re-computes instantly without re-running the model. Exports MusicXML (with tuplets, ties and harmony), MIDI, SVG, PNG, and PDF or print on Letter or A4 paper with whole lines of music on every page.

Cut a region out of any audio file, exact to the sample and measured at zero milliseconds of error. Waveform handles, real keyboard shortcuts, click-free cut fades, and WAV or MP3 output that matches its extension.

Normalize to real ITU-R BS.1770-4 loudness, within 0.04 LU of ffmpeg, with an enforced true peak ceiling. Measures the processed file and shows where it actually landed.

Turn audio into a waveform image in five styles, exported as PNG or real vector SVG. Reads every channel, shows true level in dBFS, and redraws correctly at any size.

Detect tempo from onset autocorrelation, within 0.20 BPM across thirteen known-tempo fixtures. Draws the beats it found and plays them back as a click so you can check by ear.

Attenuate everything below a threshold by a set number of dB, with hold, hysteresis and lookahead. Draws the gain reduction over the waveform and reports what it measured.

Record from a microphone with the browser's call processing off by default, a level meter in real dBFS with a clipping indicator, and a length taken from the audio rather than the clock.

Sample-accurate metronome from 20 to 400 BPM: no drift, tap tempo, subdivisions, swing, odd meters with correct accent groupings, a speed trainer, dropped bars, and WAV click-track export.

Convolution reverb with a reverberation time you set in seconds and the tool measures back off the response it built. Deterministic, so the download is the reverb you previewed; the impulse response is downloadable too.

Cut a ringtone, notification or alarm from any audio file, snap it to the beat so a repeat does not stutter, and set it to a loudness that holds up against the phone's own tones. Exports .m4r, .mp3 and WAV.

Find silent sections across every channel, not just the left. Threshold, hysteresis, minimum length, and cut padding all re-run instantly. Export a tightened WAV or MP3, split into clips as one ZIP, or save the timeline as CSV or JSON.

Read text aloud with any voice your system provides, with sentence-by-sentence progress that works even for voices that report no word boundaries, and a reading-time estimate calibrated from the voice you pick.

Generate band-limited test tones, sweeps and noise from 20 Hz to 20 kHz. Up to eight voices, note-name entry, binaural beats, and WAV export rendered from the same oscillators you hear.

Pull centred content out of a stereo mix by spectral masking or phase cancellation, with both stems from one pass and a measured report of how far the vocal moved and what it cost everything else.

Real pitch shifting in semitones that keeps the recording the same length, with speed as a separate control. Nine presets plus ring modulation, distortion, filters and echo.

Remove a coloured background, with a preview that runs the export own arithmetic. Eyedropper colour picking, two named similarity measures, spill suppression, and a choice between a transparent MOV and a composite onto a new background.

Record a screen, a window or a browser tab with system audio, your microphone, both or neither. The finished WebM carries its own length, so it seeks and scrubs where a plain browser recording reports no duration at all. Nothing is uploaded.

Re-encode a video smaller with H.264 CRF, a speed preset that really reaches the encoder, and a downscale that keeps the shape. Measures a sample to predict the size, then shows what the file actually came out as.

Cut a rectangle out of every frame, with the selection drawn over the picture itself and held in source pixels. Numeric entry, shape and platform presets, and the even-number rounding H.264 forces printed before it is applied rather than after.

Convert a video between MP4, WebM, OGG, MOV, AVI and MKV, each naming the codecs it really writes and each producing a file that actually plays. One quality dial normalised into four different encoder scales.

Reads your file's real frame rate with FFmpeg, then converts to 24, 30, 60, 120 fps or any custom rate. Frame duplication, blending, or true motion interpolation, with CRF quality control and a verified output readout.

Repeat a clip by count or to a target length, and choose what happens at the joint: a hard cut that copies without re-encoding, a boomerang, a cross blend or a fade through black. For Stories, backgrounds and cinemagraphs.

Join clips end to end, saying in advance whether they can be stitched together untouched and, when they cannot, exactly which differences stop it. Clips of different sizes are letterboxed into one frame rather than squashed.

Remove, silence or re-level the soundtrack without re-encoding a single frame. The picture is copied bit for bit, and the output keeps your container with an audio codec it can hold. No uploads, everything runs in your browser.

Encode by constant quality (CRF), average bitrate, or an exact target file size with two-pass. Aspect-safe scaling from 360p to 1440p, audio and container control, and a measured SSIM quality score on the result.

Play a video backwards, or forward and then backward, at a speed that reaches the file. Reverse the sound, keep it running forwards, or drop it. The memory a reversal needs is worked out from your own clip.

Turn or mirror a video in the pixels rather than in a container flag, so it is upright everywhere. Says where each edge of the source will end up, composes the turn and the mirror in a stated order, and always writes MP4.

Speed a video up or slow it down, choosing what happens to the pitch (time stretch or resample) and to the frames (keep the rate or keep every frame). Both choices reach the export, and the finished length is read back off the file.

Burn subtitles permanently into the picture. SubRip, WebVTT and Advanced SubStation all read, every cue listed with the exact frames it covers, and the styling set as a percentage of the frame.

Take frames out of a video by index rather than by guesswork. The frame rate is measured, every image is labelled with the frame it came from, and they all come down as one ZIP archive.

Take the soundtrack out of a video. Copy the existing track sample for sample, or re-encode to MP3, M4A, AAC, OGG, WAV or FLAC with the cost of that choice stated before you run it.

Convert a video clip to an animated GIF with a palette built from your own frames, four dithering modes each labelled with its measured size cost, a loop count that really reaches the file, and frame rates marked for whether a GIF can hold them exactly.

Cut a clip out of a video, choosing whether the cut lands on the exact frame (re-encodes to MP4) or leaves the streams untouched (instant and lossless, but only at a keyframe). The result says which ran and reads the real length back off the file.

Add a text or logo watermark placed in the file own pixels, so the preview is where the export puts it. Nine positions, exact placement by dragging, a tiled mode a crop cannot remove, and sizes as a percentage of the frame.

Minify or beautify JavaScript, TypeScript, CSS, HTML, JSON, XML and SQL with a real lexer per language, so a comment inside a string is not deleted and a line break the code depends on is kept, with the byte saving measured

Syntax highlighting from a real lexer per language, so a URL inside a string is not read as a comment, with 22 languages, 7 themes, and HTML, PNG and copy-as-markup export

Haiku in nine themes, with every line counted after it is built from CMU Pronouncing Dictionary syllable counts rather than a spelling rule, and a seed in the link so a poem can be shared

HTML to Markdown and back, built on a real HTML tree and a CommonMark parser rather than regular expressions, with GitHub tables, a live preview, and a report of everything Markdown could not carry

Format, validate and minify JSON, JSON with comments and JSON5, without changing a single value: every number is written back as the document spelled it. Errors carry a line, a column and the offending line. JSONPath queries, tree view, schema checks and diff

Generate a JSON Schema from a document and see whether it actually validates that document, with every number written back exactly as the file spelled it and formats checked against the calendar and the clock rather than by pattern

Placeholder text in 8 styles, in exactly the word count you asked for, from a seed carried in the shared link so the same configuration reproduces the same words

Markdown editor with a live preview from a real CommonMark 0.31.2 parser, scored 580 of 652 against the specification, plus GitHub tables, task lists and strikethrough, a document outline, and .md and .html export

Build or paste a Markdown table and see it read back cell by cell, with column widths measured in display columns so CJK text, emoji and accents line up, and pipes escaped in the right order

134 printable paper templates - dot grid, graph, isometric, hex, Cornell notes, handwriting guides, planners, calendars, manuscript paper, tablature, game boards and more. True vector PDF, SVG or PNG at any paper size.

Test regex patterns with real offsets, every capture group with its own position, all eight flags including v and y, an explanation that reads the pattern rather than guessing, and a runaway pattern stopped instead of freezing the page

Format SQL from a real tokenizer, so a keyword inside a string literal stays a value, with five dialects whose string and identifier rules differ, comments kept, and the output checked by running it in sqlite

Convert text between 17 cases with every rule stated: punctuation is a separator, acronyms survive, accents survive a URL slug, and Title Case follows a style you name (Chicago, AP or APA) rather than an unattributed word list

Compare texts with side-by-side and unified diff views, line-by-line or character-level comparison, change statistics, and export to patch file

Real AES-256-GCM encryption with a passphrase, plus twelve classical ciphers and encodings that are not encryption, each stating its keyspace and what breaks it

Six readability formulas, each computed from its own publication and shown with the definition, over counts whose rules are stated: characters as a reader sees them, and sentences that know an abbreviation from the end of one

Count words, characters, sentences and paragraphs with every rule stated: characters as a reader sees them rather than as UTF-16 code units, sentences that know Dr. from the end of one, and six readability formulas each shown with the paper it comes from

Format and validate XML without changing the document: CDATA, xml:space="preserve" and mixed content all survive, with errors carrying a line, a caret and a next step, plus XPath queries, a tree view and JSON conversion that names what JSON cannot carry

Test XPath 1.0 against XML with all four result types, not just node-sets, and the namespaces your document declares bound for you including the default one

Format YAML without rewriting it: comments, anchors, quoting, block scalars, multi-document streams and the exact spelling of every number all survive, with YAML 1.1 and 1.2 both offered because the same file means different things under each

Turn pictures into a PDF at the size on paper you choose. Set the resolution a pixel count prints at, pick the paper, and see every page size and the resolution it prints at before anything is written.

List every annotation a PDF carries, including the highlights, links and stamps that have no note attached, with the author, colour, page position and reply of each.

Shrink a PDF losslessly, resample its pictures, or rasterise it

Trim what a PDF page shows, with a real preview

Running heads and page numbers, placed where the page really is

Pull out a PDF's pictures as the files it holds

Join PDFs into one document, with a bookmark for each file

Drop pages from a PDF, or keep only the ones you choose

Rearrange a PDF by drag, keystroke, preset or typed order

Encrypt a PDF with AES-256, and check the result

Turn PDF pages, counting from the rotation they already carry

Draw, type or upload a signature and place it on the page a reader sees, at a width you can state in inches, on one page or every page. Transparent, so it does not hide the line you are signing on.

Split a PDF by page, by batch, or by range

Read a PDF's text in the order a person reads it

Impose pages for folding, with the order checked

Render PDF pages at a resolution you set in dpi

Stamp a mark where the page really is, anchored or tiled

Keep and reorder chosen columns, with the list built from the widest row so a field beyond the header is not dropped

Rename columns under a stated convention, with two that would end up with the same name numbered rather than left to collide

Chain 34 cell transformations, each stating its own rule, with anything it could not do reported rather than passed through unchanged

Classify every column against a decider rather than a regex: calendar-checked dates, RFC 4291 addresses, and leading zeros kept out of integer columns

Validate columns against rules that name their definition: the email rule browsers enforce, a URL scheme allowlist, calendar-checked dates, and every failure explained

Remove duplicate rows with equality as a stated choice: case, spaces, accents and numbers each their own switch, and the rule in force shown

Diff two CSV files with the matching rule stated: a key that may repeat, or a real Myers diff, with every row accounted for

Format and validate against RFC 4180 by section, with output verified by reading it back

Combine CSV files with columns matched by name, so a reordered export still lands correctly, and every difference reported

Count what is missing in five categories that add up to the grid, with the tokens that mean missing your choice

Group and aggregate with the choices stated: what count counts, how group keys are matched, and which values were not numbers

Filter rows with each condition stating its rule: a cell that is not a number does not match a comparison, and an empty cell is not a zero

Find and replace with both halves stated: what the pattern matches, and whether $1 and $& in the replacement are patterns or text

Sort by any number of columns, with the comparison stated: numbers by value, dates by day, text by a collation you choose

Split a CSV by rows, file count, column value or a real byte-size maximum, with every input row accounted for exactly once

Per-column statistics with the definitions named: which of the nine quantile rules, sample and population deviation side by side, and why each cell was counted

Convert CSV to XLSX or ODS with cell types that keep leading zeros, long IDs and dates intact

Convert both ways, converting a type only when it reads back the same, and naming every value that cannot

Generate SQL that runs: identifiers quoted rather than stripped, values escaped per dialect, and every change to your data reported

View, sort and edit a CSV, with an undo stack that goes back exactly one step and a parse report that tells a broken quote from a ragged row

Generate linear barcodes with the quiet zone each standard requires, and read the bars back to check they are right

Encode and decode text, files and JSON as base64, base64url or hex, checked by decoding the result back

Hash files with MD5, SHA-1, SHA-2 and CRC, and verify them against a published digest or a whole checksum file

Convert between ten colour notations including Lab and OKLCH, check WCAG contrast, and simulate colour vision deficiency

Build a colour harmony that holds its lightness by rotating hue in OKLCH, with the contrast of every pair, a perceptually even tint and shade ramp, and what a colour blind reader sees

Convert between 37 currencies with the rate named, the product shown before rounding, and the rounding done to the currency's own ISO 4217 minor unit rather than to two places for everything

Encrypt a file with a password using AES-256-GCM, in a documented format that records everything needed to open it again, and read it back a megabyte at a time

Repackage a font between the bare TTF/OTF container, WOFF and WOFF2, with the result read back and checked before it is offered, plus a live preview and a correct @font-face rule

MD5, SHA-1, SHA-2 and CRC digests of text or a file, with HMAC and verification against a published digest

Sign a JSON Web Token with HS, RS, PS or ES, generate a key pair, and check the result against the verifier

Decode a JSON Web Token and, given the secret or public key, actually verify its signature. Refuses alg: none and algorithm confusion

Convert text to Morse code and back against the ITU-R M.1677-1 table, and play it with the timing the Recommendation specifies

Spell text out in the radiotelephony alphabet of ICAO Annex 10 Volume II, with the Alfa and Juliett spellings the Recommendation actually gives, and read a spelled message back

Exact conversion between any bases on BigInt, with fixed-width integer views, bitwise algebra and IEEE-754

Convert a domain between Unicode and its xn-- form, both ways at once, with the length, validity and lookalike checks that decide whether it resolves

Generate QR codes and check each one scans by decoding it back before you download it

Turn a title into a URL slug in seven formats, with diacritics folded by NFD, Greek and Cyrillic romanised, every character accounted for, and collisions reported

Convert times through the real IANA rules, flagging local times that happen twice and ones that never happen

Convert across 18 categories using exact defining factors, with the definition behind every number shown

Convert between Unix timestamps and dates in any of 400+ time zones, in seconds, milliseconds, microseconds or nanoseconds

Percent-encode and decode against four character sets, build query strings, and take a URL apart

Generate UUID v1, v3, v4, v5, v6 and v7, ULID, NanoID, CUID2 and Snowflake IDs, and read any of them back

Generate a .gitignore from 52 templates, with a panel showing exactly what git will do to a set of paths and which line decided each one, re-inclusions ordered so the order you pick the templates in cannot change the result, and any negation a parent directory blocks reported with its fix

Decode an X.509 certificate field by field, check which host names it covers, and verify that each certificate in a chain was signed by the one above it

Reusable checklists with nested items, templates and progress, kept in this browser, with a full store, a second tab and a document written by an older version all handled instead of losing them.

Pick a colour and read it back in ten notations, every one checked to parse back as the same colour. WCAG contrast ratios, the nearest CSS colour name, and colour vision simulation.

Build a cron expression and see its next runs in the zone the job will actually run in, with the day-of-month OR day-of-week rule and the daylight saving rules of crontab(5) applied

Build a Content Security Policy and see what a browser will actually apply, including the CSP3 rules that silently discard what you wrote.

Build a PKCS#10 certificate signing request with subject alternative names, RSA, ECDSA or Ed25519. Signed and verified in the page before you send it to a CA.

Build a CSS keyframe animation with the timing function held to what the specification allows: named, cubic-bezier and steps easings, a preview built from the same declarations as the copied CSS, and every problem the browser would refuse named before you paste it

Round corners in px or percent, circular or elliptical, and see the radius the browser will actually paint after the CSS overlap rule scales it down

Stack CSS box shadows with any colour notation, and never write a declaration the browser will drop: a layer that will not parse is left out and flagged rather than taking every other layer down with it

Design a CSS button and see every state measured against WCAG on the page colour you name: resting, hover, active, focus and disabled, plus the focus ring and the border.

Build a clip-path from polygons, circles, ellipses and rounded insets, with the fill rule exposed and the value checked before it is shown

Visual layout builder for CSS Flexbox and Grid where the generated CSS is the same declaration list the preview applies, checked to the pixel: twelve presets, the track list read against the CSS Grid grammar, and anything the browser will drop named

Build a CSS gradient and choose the colour space it is interpolated in, with the colour it keeps through the middle measured and shown.

Build a favicon from text, an emoji or an image and get a real favicon.ico holding 16, 32 and 48 pixel images, seven PNGs, a web app manifest and the head tags, in one archive, with the ICO parsed back from its own bytes before it is offered

25 curated Google Fonts pairings with the measurable parts measured: x-height and cap-height read off the loaded faces, weight menus offering only what each family publishes, and one link carrying exactly the weights the CSS uses

Frosted glass CSS where every setting can be set to zero, any colour notation works, and the reason backdrop-filter renders flat on a real page is written down

Encode and decode HTML character references against the full WHATWG table of 2,231 names, with the numeric remapping and the context rules a browser applies.

All 64 status codes the IANA registry has assigned, plus the 21 that nginx, Cloudflare, AWS and Laravel ship without one. Type any number and get an answer.

Build an invoice whose figures add up. Amounts on integers in the currency own ISO 4217 minor unit, fractional quantities, the discount taken before tax, and a PDF that gets written whatever alphabet the client name is in.

Write SEO, Open Graph and X card tags with every value escaped for an attribute, checked against the protocol, and the cut shown per platform.

Generate fake data that is the thing it is labelled: card numbers with a real Luhn check digit, IBANs that pass ISO 7064 MOD 97-10, UUID v4 and v7 per RFC 9562, reserved e-mail and IP ranges, a seed so the same data comes back, and JSON, NDJSON, CSV or SQL output

Paste a page head and see the card each platform actually gets: the title cut at its own limit, the image measured, and what the protocol says is missing.

Generate passwords from the Web Crypto generator by rejection sampling, with the entropy stated exactly from the alphabet, the cost of every rule computed, and crack times against four named attacker models

An upper bound on how strong a password is, from the patterns that actually make one guessable, with the model and its limits stated in full.

Convert certificates, requests, CRLs, keys and PKCS#7 bundles between PEM text and DER binary. The object type and the PEM label are read from the bytes, not asked for.

Work and break cycles on a monotonic clock, so a session is not ended by the system clock changing, with the running session and today figures kept if you reload.

Write a robots.txt by the RFC 9309 rules, then test a URL against it and see which rule wins and why.

Generate SSL/TLS certificates for local development, with hostnames placed in the Subject Alternative Name where browsers look. Exports PKCS#8, PKCS#1 and PKCS#12, with fingerprints and install config.

Build a Subresource Integrity attribute, with more than one hash if you want, and check an existing one against the file it is meant to pin.

Generate an SSH key pair in the OpenSSH format ssh-keygen writes: Ed25519, ECDSA or RSA, with the fingerprint and randomart it prints.

Read the certificate chain a server sends and say whether it is complete, in order and in date, and build the OpenSSL commands that fetch it.

Every fact about an IPv4 or IPv6 block, plus splitting, merging, range to CIDR, and which special-purpose range an address falls in

A stopwatch and a countdown on a monotonic clock, so neither loses time to a pause, a background tab or the system clock changing. Lap splits that add up, and a countdown that survives a reload.

Tasks with priorities, due dates and tags, kept in this browser, with a full store, a second tab and a document written by an older version all handled instead of losing the list.

Check a link for typosquats, brand-in-subdomain tricks, mixed-alphabet homographs, and hidden destinations. Public Suffix List parsing, explainable per-rule scoring, and the link is never fetched.

Read a user agent string and mark every field: read from a token, a frozen constant, or something the string cannot answer at all.

Your public IP address, checked against the IANA special-purpose registries so a private or shared address is named rather than called public, with the location shown as the estimate it is.

A knowledge base with double-bracket links, backlinks and tags, kept in this browser, with the storage limit shown and a refused save reported rather than losing the note.

Plot 3D surfaces from z = f(x, y), polar z = f(r, theta), or fully parametric equations. Exact evaluation via mathjs, real holes where a function is undefined, and OBJ or STL export for 3D printing.

Aspect ratios reduced exactly by the greatest common divisor, with the reduction multiplied back as a check, resizes that say whether they are exact, and named ratios that carry a note where the name is not the ratio.

Body mass index against all eight rows of the WHO adult table, each naming its source, with the pound and inch at their exact defined values and a note when the adult table does not apply.

Molar mass, equation balancing, pH and the gas laws on all 118 elements of the IUPAC 2021 table, with every interval mass and every approximation named.

Exact ages and date differences worked out on the calendar itself, with no arithmetic on milliseconds, so the answer is the same in every time zone. Shows which days are not 86,400 seconds long.

Linear, quadratic, cubic and higher equations and systems, with exact rational coefficients, numerically stable roots and each root substituted back to show its residual.

Loans, compound growth, savings goals and rates of return on integers, with an amortisation schedule whose payments add up to the total and a balance that closes at exactly zero.

Add, subtract, multiply, divide, compare and simplify fractions of any size, exactly. Reads mixed numbers and repeating decimals, and gives the decimal expansion with its repeating cycle.

The greatest common divisor and lowest common multiple of any whole numbers at any size, with the Euclidean algorithm written out, Bezout coefficients, and the two answers checked against each other.

Area, perimeter, volume and surface area for twenty-four shapes, drawn to scale, with every assumption stated and every approximation named.

Plot functions with a real expression parser, poles drawn as gaps, and roots, turning points and integrals found by bracketing with the check printed.

Determinants, inverses, eigenvalues and row reduction over exact fractions, with A times its inverse shown to be exactly the identity and the condition number reported.

Ten kinds of percentage question, answered in exact arithmetic rather than floating point, with the working shown. Includes percentage points, finding the whole, and tax both ways.

Twelve kinds of physics problem with every constant named as defined, measured or conventional, results printed to the figures those constants justify, and an independent check on each answer.

Whether a number is prime, at any size, decided by deterministic Miller-Rabin rather than trial division. Prime factorisation, every divisor, the primes either side and Goldbach pairs.

Exact arithmetic on rationals, with both evaluation conventions named and the precedence table the parser runs on printed on the page.

Mean, median, both variances, all nine quantile definitions and the moment coefficients of shape, each with the definition it is under and where to reproduce it.

Add and subtract durations with the sign kept, so one hour minus two hours is minus one hour. Also moves a time of day forward or back and says how many midnights it crossed.

The tip, the tax and everybody's share worked out in whole pennies, so the amounts printed add up to the total printed. Says who pays the odd penny, and what rounding does to the tip rate.

Truth tables with the reading printed, so A implies B implies C shows its brackets. Refuses a chain of NAND or NOR rather than guessing, and reads a name like nota as one variable.

Slide tiles to combine them and reach 2048. Each tile merges at most once per move, checked exhaustively against the rule, and the board total printed under the grid always equals everything ever spawned. Undo, touch controls and score tracking.

Casino blackjack. Hit, stand, double, split, surrender and insure. 6-deck shoe, with the 3:2 or 6:5 payout and the soft-17 rule as settings

Brick breaker with continuous collision, so the ball never passes through a brick and bounces off the face it actually hits. Power-ups, boss levels, upgrades and achievements.

Cellular automaton on a board up to 300 by 300, with RLE import and export, custom B/S rulestrings (HighLife, Seeds, Day and Night), pattern stamping, and pan and zoom.

Standard dice notation with keep, drop, advantage, exploding dice and re-rolls. Shows the exact probability before you roll, and a seed makes any roll reproducible from a shared link.

Navigate through pipes in this side-scrolling game. Fixed-timestep physics that plays the same at any frame rate, three difficulties, coins and medals

Word guessing game with 1,470 checked words across 8 categories, four difficulty bands, five modes, SVG animation and hints

Code-breaking puzzle. Guess the secret colour code from black and white pegs, with a live count of the codes still possible. Four difficulties, six modes

Card matching with eight emoji themes, four difficulty sizes and four modes. The deal is a real Fisher and Yates shuffle, measured uniform over 60,000 boards, and a turn is a state machine so two fast clicks cannot strand a card face up.

Minesweeper on the three standard boards or one of your own, with both first-click conventions offered by name: a safe square, or a safe square and its eight neighbours. Flags, question marks, chording and best times.

Colour pattern memory game with audio feedback. Repeat the sequence as it grows. Four modes, four speeds, flash and gap times printed

Snake with four modes, four power-ups and the classic tail rule: the square your tail is leaving is safe to enter, which is what lets you turn tightly inside your own body. Four speeds, per-mode high scores and touch controls.

Sudoku with a guarantee most generators skip: every puzzle is checked to have exactly one solution before you see it. Difficulty is measured by the techniques a puzzle needs, and hints say why a digit belongs where it does.

Block stacking with the Super Rotation System and its real wall kicks, so a flat I can stand up off the floor, and a 7-bag randomiser so no piece is ever more than twelve away. Hold, ghost piece and Guideline scoring.

Tic-tac-toe against a minimax opponent, or a friend on the same device. Four difficulty levels, each a stated rate of playing a move that is not the best; on Impossible it cannot be beaten, proved by walking all 16,752 games.

Trivia quiz over 455 questions in 10 categories, with the options shuffled every round so the answer is never in a predictable place. Timer, lifelines, streaks

Typing test with gross and net WPM to the standard five-character definition, character accuracy, ghost replays, six modes and three difficulties

Click-based reflex game. Whack moles for points, grab golden moles for bonus, avoid bombs! Combo system

Guess the 5-letter word in 6 tries. Colour-coded hints, repeated letters marked correctly, and a live count of the answers that still fit your clues