The glossary
281 formats, specifications and standards that the tools on this site read, write or implement. Each entry says what the thing is and lists the tools that work with it, and 39 of them cite the primary specification.
A
- A42 toolsA4 is the ISO 216 paper size of 210 × 297 mm, standard across most of the world.
- AAC3 toolsAAC (Advanced Audio Coding) is a lossy audio compression standard defined as part of MPEG-4 and designed as the successor to MP3, generally delivering better quality at the same bitrate.
- Abbreviation2 toolsAn abbreviation is a shortened form of a word or phrase.
- Accessibility3 toolsAccessibility is the practice of designing products so that people with disabilities can use them. On the web it is governed principally by WCAG.
- AcroForm3 toolsAcroForm is the interactive form technology defined in the PDF specification. Form fields — text boxes, checkboxes, radio groups, dropdowns — are PDF objects that store their own value, so a filled form remains a single PDF file.
- Advanced SubStation Alpha2 toolsAdvanced SubStation Alpha (.ass) is a subtitle format that extends SubStation Alpha with named styles, positioning and drawing commands, so it can carry typesetting that SubRip cannot.
- Amortisation2 toolsAmortisation is the repayment of a loan through scheduled instalments, each covering interest owed and part of the principal.
- Android TV2 toolsAndroid TV is Google’s version of Android for televisions and set-top boxes.
- Animation2 toolsAnimation is the presentation of a sequence of images or property changes over time to create the appearance of motion.
- Annotation2 toolsAn annotation is a note or mark added to a document without altering its underlying content.
- Anthropic2 toolsAnthropic is an AI safety and research company, and the developer of the Claude family of models.
- Apache HTTP Server3 toolsThe Apache HTTP Server is an open-source web server maintained by the Apache Software Foundation, extensible through modules and configurable per directory via .htaccess files.
- API2 toolsAn API (application programming interface) is the defined contract through which one piece of software is used by another — the operations available, their inputs and their outputs.
- App Store3 toolsThe App Store is Apple’s distribution platform for iOS, iPadOS and macOS applications.
- Arithmetic2 toolsArithmetic is the branch of mathematics dealing with the basic operations on numbers: addition, subtraction, multiplication and division.
- ASCII art3 toolsASCII art composes pictures out of printable text characters, originally because early terminals and printers could output nothing else.
- Aspect ratio5 toolsAspect ratio is the proportional relationship between an image’s width and height, written as w:h. Preserving it while resizing is what prevents distortion.
- Avatar2 toolsAn avatar is the image representing a person or account in an interface.
- axios2 toolsaxios is a JavaScript HTTP client library for browsers and Node.js, built around promises, with interceptors and automatic JSON handling.
B
- Bandwidth2 toolsBandwidth is the maximum rate at which data can be transferred over a connection, normally given in bits per second.
- Barcode5 toolsA barcode encodes data in a machine-readable pattern. One-dimensional symbologies use bars and spaces; two-dimensional ones such as QR use a matrix of cells.
- Basal metabolic rate2 toolsBasal metabolic rate is the energy the body uses at complete rest to maintain basic functions. Estimating equations such as Mifflin–St Jeor approximate it from height, weight, age and sex.
- Base647 toolsBase64 encodes arbitrary binary data as 64 printable ASCII characters, so it can pass through text-only channels such as email or JSON. It expands the data by about a third and provides no secrecy.
- bcrypt2 toolsbcrypt is a password-hashing function built on the Blowfish cipher, with a deliberately adjustable cost factor so hashing can be made slower as hardware gets faster.
- Bézier curve2 toolsA Bézier curve is a parametric curve defined by a start point, an end point and one or more control points that pull the line between them. Quadratic and cubic Béziers are what font outlines, vector graphics and CSS easing functions are built from.
- Bidirectional text2 toolsBidirectional text mixes left-to-right and right-to-left scripts in one run. Unicode defines an algorithm, plus explicit control characters, for deciding the visual order.
- Binary number2 toolsA binary number is written in base 2, using only the digits 0 and 1. Each position represents a power of two, which matches how hardware stores values.
- BMP2 toolsBMP is an uncompressed raster image format originating on Microsoft Windows. Pixels are stored directly, which makes files large but trivially simple to read and write.
- Border radius2 toolsThe CSS border-radius property rounds an element’s corners. Each corner can take two radii, producing an elliptical rather than circular curve.
- Brotli6 toolsBrotli is a lossless compression algorithm developed at Google, using a large predefined dictionary tuned for web content. It generally compresses better than gzip and is the compression inside WOFF2.
- Burstiness2 toolsBurstiness describes how unevenly a quantity is distributed over a sequence. Applied to text, it refers to variation in sentence length and complexity, which tends to be higher in human writing than in unedited model output.
- Business day3 toolsA business day is a day on which normal business is conducted — typically Monday to Friday, excluding public holidays, which vary by jurisdiction.
- Byte pair encoding2 toolsByte pair encoding builds a subword vocabulary by repeatedly merging the most frequent adjacent pair of symbols in a corpus. It is the tokenisation scheme behind most current language models.
C
- Caesar cipher2 toolsThe Caesar cipher shifts every letter of the alphabet by a fixed number of positions. It offers no real security — there are only 25 possible shifts — and survives as a teaching example.
- CAGR2 toolsThe compound annual growth rate is the constant yearly rate that would take an investment from its starting value to its ending value over a given period. It smooths away volatility along the way.
- Calendar date2 toolsA calendar date identifies a single day within a calendar system, normally by year, month and day.
- Calorie4 toolsA calorie in nutrition (strictly a kilocalorie) is a unit of food energy, equal to about 4.184 kilojoules.
- Camel case3 toolsCamel case joins words without separators and capitalises each word after the first, as in backgroundColor.
- Canvas API4 toolsThe Canvas API exposes a bitmap drawing surface to JavaScript through the <canvas> element, with 2D and WebGL/WebGPU contexts for shapes, text, images and pixel manipulation.
- Checksum2 toolsA checksum is a short value computed from a block of data and used to detect accidental corruption. It is designed against transmission errors, not against a deliberate attacker.
- Claude2 toolsClaude is a family of large language models developed by Anthropic.
- clip-path3 toolsThe CSS clip-path property restricts an element’s visible area to a shape — a basic shape function, an SVG path, or a reference to a <clipPath> element.
- Closed captioning2 toolsClosed captions are a text track carrying dialogue and relevant non-speech sound, which the viewer can turn on or off. Unlike subtitles, they are intended for viewers who cannot hear the audio.
- Code point4 toolsA code point is the numeric value Unicode assigns to a character, written as U+ followed by hexadecimal digits. One user-perceived character may be several code points, and one code point may be several bytes.
- Color quantization2 toolsColour quantisation reduces an image to a limited palette, choosing representative colours and mapping every pixel to the nearest one. It is how GIF and indexed PNG files are produced.
- Color scheme2 toolsA colour scheme is a deliberate set of colours used together in a design, chosen by relationships such as complementary, analogous or triadic.
- Combination2 toolsA combination is a selection of items from a set where order does not matter, in contrast to a permutation, where it does.
- CommonMark10 toolsCommonMark is a specification that defines precise, unambiguous parsing rules for Markdown. It exists because the original Markdown description left many cases undefined, so different implementations disagreed.
- Compact Font Format6 toolsCompact Font Format (CFF) is a compressed representation of PostScript Type 1 outlines, using cubic Bézier curves. It is the outline format inside OpenType fonts with the .otf extension.
- Compound interest6 toolsCompound interest is interest calculated on the principal plus the interest already accumulated, so the balance grows faster than under simple interest.
- Configuration file2 toolsA configuration file stores settings for a program outside its source code, so behaviour can change without recompiling. Common formats include INI, JSON, YAML, TOML and dotenv files.
- Content Security Policy3 toolsContent Security Policy is an HTTP response header that tells the browser which sources a page may load scripts, styles, frames and other resources from. It is a defence-in-depth measure against cross-site scripting.
- Corpus linguistics2 toolsCorpus linguistics studies language through statistical analysis of large collections of real-world text.
- Cosine similarity3 toolsCosine similarity measures the cosine of the angle between two vectors, giving a value from −1 to 1 that reflects orientation rather than magnitude. It is the standard similarity measure for text embeddings.
- cron2 toolscron is the time-based job scheduler on Unix-like systems, running commands at times given by a five- or six-field schedule expression.
- crontab2 toolsA crontab is the file listing scheduled jobs for cron, one per line, each pairing a schedule expression with a command.
- Cross-site scripting2 toolsCross-site scripting is a vulnerability in which an attacker gets their script executed in another user’s browser in the context of a trusted site, usually because input was rendered without escaping.
- Cryptographic hash function4 toolsA cryptographic hash function maps input of any length to a fixed-length digest, such that finding two inputs with the same digest, or recovering an input from its digest, is computationally infeasible.
- Cryptography2 toolsCryptography is the study and practice of techniques for securing information — confidentiality, integrity, authentication and non-repudiation — against adversaries.
- CSPRNG3 toolsA cryptographically secure pseudorandom number generator produces output that is computationally indistinguishable from random and cannot be predicted from previous output. In browsers it is exposed as crypto.getRandomValues().
- CSS24 toolsCSS (Cascading Style Sheets) is the language that describes how HTML is presented — layout, colour, typography and animation. It is developed by the W3C CSS Working Group.
- CSS animations3 toolsCSS animations interpolate property values over time using an @keyframes rule and the animation properties, without requiring JavaScript.
- CSV16 toolsCSV (comma-separated values) is a plain-text tabular format in which each line is a row and fields are separated by commas. It has no single formal standard; RFC 4180 describes the most common conventions.
- curl2 toolscurl is a command-line tool and library for transferring data over URLs, supporting HTTP and many other protocols. Its command syntax is a common way to share reproducible API requests.
D
- Data compression2 toolsData compression re-encodes data to occupy fewer bytes. Lossless compression reconstructs the original exactly; lossy compression discards information judged less perceptible in exchange for smaller output.
- Data URI5 toolsA data URI embeds a file’s bytes directly in a URL using the data: scheme, usually Base64-encoded. It removes a network request at the cost of a larger, uncacheable document.
- Data validation2 toolsData validation is the process of checking that input conforms to expected types, ranges, formats and required fields before it is stored or acted on.
- Daylight saving time2 toolsDaylight saving time is the seasonal practice of shifting clocks forward, so that evenings have more daylight. Its start and end dates vary by jurisdiction and change over time.
- Decimal3 toolsDecimal is base-10 notation, the standard positional number system using the digits 0 through 9.
- Deduplication2 toolsDeduplication removes redundant copies of repeated data, keeping one instance and referencing it.
- Diff3 toolsA diff is a representation of the differences between two texts, listing the lines added, removed and unchanged.
- Display resolution2 toolsDisplay resolution is the number of distinct pixels a screen shows, given as width × height.
- DMARC2 toolsDMARC builds on SPF and DKIM: a DNS record states what a receiver should do with mail that fails those checks, and where to send aggregate reports. It is defined in RFC 7489.
- DNS2 toolsThe Domain Name System translates human-readable domain names into IP addresses, through a distributed hierarchy of servers. Its core behaviour is defined in RFC 1035.
- Document editing2 toolsDocument editing is the modification of a document’s content, structure or formatting.
- Document properties2 toolsDocument properties are the metadata stored alongside a document’s content — title, author, subject, keywords, and creation and modification dates. Most formats keep them in a dedicated section separate from the visible text.
- DOCX18 toolsDOCX is the Microsoft Word document format introduced with Office 2007. A .docx file is a ZIP archive of Office Open XML parts rather than the single binary stream used by the older .doc format.
- DOMParser10 toolsDOMParser is a browser API that parses a string of HTML or XML into a DOM document, allowing markup to be traversed and queried without inserting it into the live page.
E
- Ed255192 toolsEd25519 is a public-key signature scheme using Edwards-curve digital signatures over Curve25519. It offers short keys and signatures with strong security and fast verification.
- Electronic signature2 toolsAn electronic signature is data attached to a document indicating the signer’s intent to agree to it. It is a legal concept, and is broader than a cryptographic digital signature.
- Email2 toolsEmail is the store-and-forward messaging system of the internet, carried by SMTP and addressed as a local part and a domain separated by an @ sign.
- Embedding2 toolsAn embedding is a dense vector representation of text, images or other data, positioned so that similar items lie close together. Similarity is normally measured by cosine distance.
- English numerals2 toolsEnglish numerals are the written-out words for numbers, such as "forty-two" for 42.
- Entropy5 toolsIn information theory, entropy measures how unpredictable a value is, expressed in bits. Applied to passwords and keys, it estimates how much work a brute-force search would take.
- Environment variable2 toolsAn environment variable is a named value held by the operating system process and readable by the programs it runs. Deployments use them to supply configuration and secrets without committing them to source control.
- EPUB3 toolsEPUB is an open e-book format maintained by the W3C. An EPUB file is a ZIP archive of XHTML content, styling and metadata, and its text reflows to fit the reader’s screen rather than sitting on fixed pages.
- Escape sequence2 toolsAn escape sequence is a character combination that represents a character which cannot be written literally in the surrounding context — for example \n for a newline inside a quoted string.
- Exif2 toolsExif (Exchangeable image file format) is the metadata standard cameras and phones use to record capture settings inside a photo — exposure, lens, timestamp, and often GPS coordinates.
F
- Favicon2 toolsA favicon is the small icon a browser shows for a site in tabs, bookmarks and history. Sites supply it at /favicon.ico or through a <link rel="icon"> element, usually in several sizes.
- Fetch API2 toolsThe Fetch API is the browser interface for making HTTP requests from JavaScript, returning a promise for a Response. It replaced XMLHttpRequest as the standard approach.
- FFmpeg10 toolsFFmpeg is an open-source project providing libraries and command-line tools for decoding, encoding, transcoding and filtering audio and video. Most media software depends on it somewhere in the stack.
- Fine-tuning2 toolsFine-tuning continues training a pretrained model on a smaller, task-specific dataset, adapting its behaviour without training from scratch.
- Fisher–Yates shuffle4 toolsThe Fisher–Yates shuffle produces an unbiased random permutation of a sequence by walking it from the end and swapping each element with a randomly chosen earlier one. Each permutation is equally likely.
- Fraction2 toolsA fraction represents a part of a whole as a numerator over a denominator.
- Frequency analysis2 toolsFrequency analysis breaks classical ciphers by comparing how often symbols appear in the ciphertext with their known frequency in the underlying language.
G
- GDPR5 toolsThe General Data Protection Regulation is European Union law governing the processing of personal data. It applies to any organisation handling data about people in the EU, wherever that organisation is based.
- getUserMedia3 toolsgetUserMedia() is the browser API that requests access to the user’s camera or microphone and resolves to a MediaStream. It requires a secure context and explicit user permission.
- GGUF2 toolsGGUF is the file format used by llama.cpp to store quantised model weights together with their metadata and tokeniser in a single file.
- GIF3 toolsGIF (Graphics Interchange Format) is a lossless raster format limited to a 256-colour palette per frame, with support for animation and single-colour transparency.
- Git5 toolsGit is a distributed version control system that records project history as a graph of commits. Every clone contains the full history.
- GitHub Flavored Markdown4 toolsGitHub Flavored Markdown (GFM) is GitHub’s dialect of Markdown, defined as a strict superset of CommonMark. It adds tables, task lists, strikethrough and automatic link detection.
- Google Gemini2 toolsGemini is a family of multimodal large language models developed by Google DeepMind.
- Google Play3 toolsGoogle Play is Google’s distribution platform for Android applications and other digital content.
- Gradient2 toolsA gradient is a gradual transition between colours. CSS generates them as images through linear-gradient(), radial-gradient() and conic-gradient().
- GraphQL2 toolsGraphQL is a query language for APIs in which the client states exactly which fields it needs and receives just those fields. A GraphQL service exposes a single endpoint backed by a typed schema.
- Gratuity2 toolsA gratuity, or tip, is a sum given to a service worker beyond the stated price. Expectations vary widely between countries.
- Greatest common divisor4 toolsThe greatest common divisor of two or more integers is the largest integer that divides all of them without remainder. Euclid’s algorithm computes it efficiently.
- Gregorian calendar2 toolsThe Gregorian calendar is the civil calendar in general use, introduced in 1582 as a refinement of the Julian calendar’s leap-year rule.
- Gross margin2 toolsGross margin is revenue minus cost of goods sold, expressed as a percentage of revenue.
- GST2 toolsGST (goods and services tax) is a value-added tax levied on most goods and services sold for domestic consumption, collected at each stage of the supply chain.
H
- H.2642 toolsH.264 (Advanced Video Coding) is a block-oriented video compression standard published jointly by ITU-T and ISO/IEC. It is the most widely supported video codec in browsers and hardware decoders.
- Hexadecimal4 toolsHexadecimal is base-16 notation, using the digits 0–9 and letters A–F. One hex digit represents exactly four bits, which makes it a compact way to write binary data.
- HMAC4 toolsHMAC is a construction for message authentication that combines a secret key with a cryptographic hash function, letting a recipient verify both the integrity and the origin of a message.
- Homoglyph2 toolsA homoglyph is a character that looks like another — Cyrillic а against Latin a, for instance. Domain names and identifiers exploiting the resemblance are a recognised spoofing vector, which Unicode addresses in its security reports.
- HSL and HSV2 toolsHSL and HSV are cylindrical representations of RGB colour. Both use hue and saturation; HSL’s third axis is lightness and HSV’s is value, which is why the same numbers mean different colours in each.
- HTML14 toolsHTML (HyperText Markup Language) is the markup language that defines the structure and content of web pages. It is maintained by the WHATWG as a continuously updated Living Standard.
- HTTP2 toolsHTTP (HyperText Transfer Protocol) is the request/response protocol underlying the web. Its semantics — methods, status codes and headers — are defined in RFC 9110.
- HTTP header2 toolsAn HTTP header is a name/value field carried with a request or response, conveying metadata such as content type, caching rules, authentication and security policy.
- HTTP Strict Transport Security2 toolsHTTP Strict Transport Security is a response header instructing the browser to contact a site only over HTTPS for a stated period, preventing downgrade to plain HTTP. It is defined in RFC 6797.
I
- IANA time zone database2 toolsThe IANA time zone database (also called tz or the Olson database) is the canonical record of the world’s time zones and their historical offset and daylight-saving changes. Zones are named Area/Location, such as Europe/London.
- Image editing2 toolsImage editing is the alteration of images — cropping, adjusting, retouching or compositing.
- Image scaling2 toolsImage scaling resizes a raster image, interpolating pixel values. Enlarging cannot recover detail that was never captured.
- Image segmentation2 toolsImage segmentation partitions an image into regions, labelling which pixels belong to which object or class.
- Interest rate2 toolsAn interest rate is the proportion of a principal charged or earned over a period, normally quoted per year.
- Internationalised domain name2 toolsAn internationalised domain name contains characters outside the ASCII set used by traditional host names. It is transmitted in Punycode form, which begins with the prefix xn--.
- Investment2 toolsAn investment is an asset acquired with the expectation of generating income or appreciating in value.
- ISO 86016 toolsISO 8601 is the international standard for representing dates and times, giving the ordering and punctuation behind formats such as 2024-03-17T09:30:00Z.
- ISO week date2 toolsThe ISO week date system numbers weeks from 1 to 52 or 53, with weeks starting on Monday and week 1 being the week containing the first Thursday of the year.
J
- JavaScript2 toolsJavaScript is the programming language of the web, standardised as ECMAScript. It runs in browsers and, through runtimes such as Node.js, on servers.
- JPEG4 toolsJPEG is a lossy raster image compression standard designed for photographs, published by the Joint Photographic Experts Group. Its quality setting trades visible detail for file size, and it has no transparency channel.
- JSON20 toolsJSON (JavaScript Object Notation) is a text-based data interchange format built from objects, arrays, strings, numbers, booleans and null. It is specified by RFC 8259 and ECMA-404.
- JSON Lines3 toolsJSON Lines is a text format in which each line is one complete, self-contained JSON value. Because records are newline-delimited, a file can be streamed and appended to without re-parsing what came before.
- JSON Schema3 toolsJSON Schema is a vocabulary for describing the structure of JSON data — the expected types, required properties and value constraints — so documents can be validated automatically.
- JSON Web Token3 toolsA JSON Web Token is a compact, URL-safe token carrying JSON claims in three Base64url segments: header, payload and signature. The payload is signed, not encrypted, so anyone holding the token can read it.
- JSONPath2 toolsJSONPath is a query syntax for selecting values inside a JSON document, in the way XPath selects nodes inside XML. Expressions navigate with dot and bracket notation and support wildcards and filters.
K
L
- Large language model5 toolsA large language model is a neural network trained on very large text corpora to predict the next token, and used to generate and transform text. Its capabilities scale with model size and training data.
- Leap year3 toolsA leap year contains an extra day, 29 February, keeping the calendar aligned with the solar year. In the Gregorian calendar a year is a leap year if divisible by 4, except centuries not divisible by 400.
- Llama2 toolsLlama is a family of open-weight large language models released by Meta.
- llama.cpp2 toolsllama.cpp is an open-source C/C++ inference engine for running large language models locally on CPUs and consumer GPUs, using the GGUF format.
- Longest common subsequence2 toolsThe longest common subsequence problem finds the longest sequence of elements appearing in the same order in two inputs, though not necessarily contiguously. It is the basis of most text diff algorithms.
- Luhn algorithm2 toolsThe Luhn algorithm is a checksum formula that validates identification numbers such as payment card numbers. It catches single-digit typos and most transpositions, and provides no security.
M
- Macronutrient2 toolsMacronutrients are the nutrients the body needs in large amounts — protein, carbohydrate and fat — and the ones that supply energy.
- Magic number2 toolsA magic number is a fixed byte sequence at the start of a file that identifies its format, letting software detect a file’s type from its contents rather than its extension.
- Markdown16 toolsMarkdown is a lightweight markup syntax that uses plain-text conventions — asterisks, hashes and brackets — to indicate formatting, and converts to HTML. It was introduced by John Gruber in 2004.
- Material Design2 toolsMaterial Design is Google’s open design system, specifying components, layout, motion and colour for applications across platforms.
- MediaRecorder2 toolsMediaRecorder is the browser API that records a MediaStream — from a camera, microphone or screen capture — into an encoded audio or video file.
- Meta element4 toolsA <meta> element carries document metadata that has no other HTML element — the character set, viewport settings, page description and robots directives among them.
- Metadata3 toolsMetadata is data describing other data — when a file was made, by what, in what format, and what it contains.
- Microsoft Excel15 toolsMicrosoft Excel is a spreadsheet application developed by Microsoft. Its current file format is XLSX; earlier versions used the binary .xls format.
- Microsoft PowerPoint11 toolsMicrosoft PowerPoint is a presentation program developed by Microsoft. Its current file format is PPTX; earlier versions used the binary .ppt format.
- Microsoft Word19 toolsMicrosoft Word is a word processor developed by Microsoft. Its current file format is DOCX; earlier versions used the binary .doc format.
- MIME type3 toolsA MIME type — now formally a media type — labels the format of a file or HTTP body, written as type/subtype, such as text/html or image/png. IANA maintains the registry.
- Minification2 toolsMinification removes characters that a parser does not need — whitespace, comments, long identifiers — from code, reducing transfer size without changing behaviour.
- Mockup3 toolsA mockup is a realistic static representation of a design, used to show how it will look before it is built.
- MP33 toolsMP3 (MPEG-1 Audio Layer III) is a lossy audio compression format that discards sound detail listeners are least likely to notice. It was the format that made digital music distribution practical, and it plays essentially everywhere.
- MP43 toolsMP4 (MPEG-4 Part 14) is a container format that holds video, audio, subtitle and metadata tracks in one file. It is a container, not a codec — the video inside is typically H.264 or H.265.
- MySQL2 toolsMySQL is an open-source relational database management system, widely deployed as the data store behind web applications.
N
- Natural language processing2 toolsNatural language processing is the field concerned with enabling computers to process and generate human language.
- nginx4 toolsnginx is an open-source web server, reverse proxy and load balancer, known for its event-driven concurrency model.
- Nutrition2 toolsNutrition is the study of how food supplies the nutrients an organism needs to sustain life and health.
O
- OCR5 toolsOptical character recognition converts images of text — scans, photographs, screenshots — into machine-readable characters.
- Office Open XML45 toolsOffice Open XML is the file format behind the modern Microsoft Office extensions .docx, .xlsx and .pptx. Each file is a ZIP archive containing XML parts that describe the document content, styling and relationships.
- Open Graph7 toolsThe Open Graph protocol is a set of <meta> properties (og:title, og:description, og:image and others) that control how a URL is presented when shared on social platforms.
- OpenAI2 toolsOpenAI is an AI research company, known for the GPT model family, DALL·E and Whisper.
- OpenAPI4 toolsOpenAPI is a specification for describing HTTP APIs in a machine-readable document. From one description, tooling can generate client libraries, server stubs, documentation and request validation.
- OpenType6 toolsOpenType is a font format built on TrueType that can carry either TrueType (quadratic) or Compact Font Format (cubic) outlines, and adds advanced typographic features such as ligatures and alternates. Files carry .otf or .ttf.
- Opportunity cost2 toolsOpportunity cost is the value of the best alternative given up when a choice is made.
- OWASP4 toolsOWASP (the Open Worldwide Application Security Project) is a non-profit that publishes freely available application-security guidance, including the OWASP Top 10 lists of common risks.
P
- Pagination2 toolsPagination divides a long body of content into discrete pages, both in printed documents and in interfaces that load results in batches.
- Password strength2 toolsPassword strength describes how resistant a password is to guessing. It depends on unpredictability rather than on any particular mix of character classes, and reused passwords are weak whatever their composition.
- PDF68 toolsPDF (Portable Document Format) is a page-description file format that fixes the layout, fonts and images of a document so it renders the same on any device. It was created by Adobe and is standardised as ISO 32000.
- PDF form3 toolsA PDF form is a PDF that contains interactive fields a reader can fill in. PDF supports two mechanisms: AcroForm, defined in the core specification, and the now-deprecated XFA.
- pdf-lib5 toolspdf-lib is a JavaScript library for creating and modifying PDF documents in the browser or in Node.js, without a server.
- pdf.js28 toolspdf.js is an open-source PDF renderer written in JavaScript and maintained by Mozilla. It is the viewer built into Firefox, and it lets browsers display PDFs without a plugin.
- PEM2 toolsPEM is a text container for binary cryptographic material: DER bytes are Base64-encoded and wrapped in BEGIN and END header lines naming the content type.
- Percent-encoding4 toolsPercent-encoding replaces characters that are unsafe or reserved in a URI with a percent sign followed by two hexadecimal digits. It is defined in RFC 3986.
- Percentage2 toolsA percentage expresses a number as a fraction of 100.
- Perplexity2 toolsPerplexity measures how well a language model predicts a text sample: the lower the value, the less surprised the model is by what it sees.
- Personal finance2 toolsPersonal finance covers how individuals budget, save, borrow, insure and invest.
- Phishing2 toolsPhishing is an attack that impersonates a trusted party to get the victim to reveal credentials or take a harmful action.
- PNG9 toolsPNG (Portable Network Graphics) is a lossless raster image format with support for full alpha transparency. It is standardised by the W3C and ISO/IEC 15948.
- PostgreSQL2 toolsPostgreSQL is an open-source object-relational database management system, known for standards conformance and extensibility.
- PPTX13 toolsPPTX is the Microsoft PowerPoint presentation format introduced with Office 2007. Slides, layouts and embedded media are stored as Office Open XML parts inside a ZIP archive.
- Prettier6 toolsPrettier is an opinionated code formatter that reprints source from its syntax tree to a consistent style, removing formatting from code review.
- Privacy4 toolsPrivacy is a person’s ability to control what information about them is collected, retained and shared.
- Prompt caching2 toolsPrompt caching lets an API reuse the processed form of a repeated prompt prefix across requests, reducing latency and the cost of the cached portion.
- Prompt engineering2 toolsPrompt engineering is the practice of writing and structuring model inputs to get more reliable or more useful outputs.
- Prompt injection2 toolsPrompt injection is an attack on a language-model application in which text drawn from an untrusted source is interpreted as instructions, causing the model to ignore or subvert the developer’s own.
- Punycode2 toolsPunycode encodes Unicode strings using only the ASCII characters permitted in host names, so internationalised domain names can travel through DNS unchanged. It is defined in RFC 3492.
Q
- QR code6 toolsA QR code is a two-dimensional matrix barcode readable by a camera, defined by ISO/IEC 18004. Built-in error correction lets it still scan when partly damaged or obscured.
- Quantization2 toolsQuantisation stores a model’s weights at lower numeric precision — 8-bit or 4-bit instead of 16-bit floats — cutting memory use substantially at some cost in accuracy.
- Query string4 toolsThe query string is the part of a URL after the question mark, carrying key/value parameters separated by ampersands. Values must be percent-encoded.
- Question answering4 toolsQuestion answering is the task of producing a direct answer to a natural-language question, rather than a list of documents.
- Quishing4 toolsQuishing is phishing carried out through QR codes: the code hides the destination URL, so the victim cannot inspect the link before their camera opens it.
R
- Radian2 toolsA radian is the SI unit of angle: the angle subtended at the centre of a circle by an arc equal in length to the radius. A full turn is 2π radians.
- Randomness5 toolsRandomness is the absence of pattern or predictability in a sequence. Security-sensitive work requires a cryptographically secure generator, not the ordinary one built into a language.
- Raster graphics2 toolsA raster graphic stores an image as a grid of pixels, each with its own colour value. Enlarging one past its native resolution reveals the grid, which is what separates raster formats from vector formats.
- Ratio2 toolsA ratio expresses the relative size of two or more quantities, written as a:b.
- README2 toolsA README is the introductory document at the root of a software project, explaining what it is, how to install it and how to use it. Code-hosting platforms render it on the repository landing page.
- Redaction2 toolsRedaction is the permanent removal of sensitive content from a document. Drawing a black rectangle over text in a PDF is not redaction: the text remains selectable underneath.
- Regular expression5 toolsA regular expression is a pattern describing a set of strings, used to search, validate and replace text. Flavours differ between languages in syntax and supported features.
- Relative luminance2 toolsRelative luminance is the brightness of a colour normalised to a 0–1 scale, computed from gamma-corrected RGB components. WCAG contrast ratios are calculated from it.
- Responsive web design4 toolsResponsive web design adapts a single layout to any viewport using fluid grids, flexible images and media queries, rather than serving separate mobile and desktop sites.
- REST3 toolsREST is an architectural style for networked applications in which resources are identified by URLs and manipulated through the standard HTTP methods, with each request carrying everything needed to process it.
- Retrieval-augmented generation6 toolsRetrieval-augmented generation retrieves relevant documents at query time and puts them in a language model’s context, so answers can draw on sources outside the model’s training data.
- RFC 46483 toolsRFC 4648 is the IETF specification defining the Base16, Base32 and Base64 data encodings, including their alphabets, padding rules and URL-safe variants.
- robots.txt3 toolsrobots.txt is a file at the root of a site that tells compliant crawlers which paths they may request. It controls crawling, not indexing — a blocked URL can still be indexed from external links.
- Roman numerals2 toolsRoman numerals represent numbers with the letters I, V, X, L, C, D and M, combined by addition and by subtraction when a smaller value precedes a larger one.
- ROT132 toolsROT13 is a Caesar cipher with a shift of 13, which makes encoding and decoding the same operation. It is used to hide spoilers, not to provide security.
- RSA2 toolsRSA is a public-key cryptosystem whose security rests on the difficulty of factoring large integers. It is used for digital signatures and key exchange.
- RTF1 toolRTF (Rich Text Format) is a plain-text document format that encodes formatting as backslash control words. Microsoft published it as an interchange format readable by most word processors.
S
- Screen reader4 toolsA screen reader is assistive software that conveys on-screen content as speech or braille. It relies on document structure and accessible names, which is why semantic markup matters.
- Screenshot2 toolsA screenshot is a captured image of what is displayed on a screen at a moment in time.
- Selector2 toolsA CSS selector is the pattern that decides which elements a style rule applies to, matching on element type, class, id, attribute, state or position.
- Semantic HTML4 toolsSemantic HTML uses elements that describe the meaning of their content — <nav>, <article>, <header>, <button> — rather than generic containers. It is what gives assistive technology and search engines structure to work with.
- Semantic Versioning2 toolsSemantic Versioning is a version-numbering convention of MAJOR.MINOR.PATCH, where a major bump signals a breaking change, a minor bump a backwards-compatible feature, and a patch bump a fix.
- Sender Policy Framework2 toolsSender Policy Framework is a DNS record listing which servers are permitted to send mail for a domain, so a receiving server can detect forged envelope senders. It is defined in RFC 7208.
- Sentence transformers2 toolsSentence Transformers is a library and family of models that produce embeddings for whole sentences and passages, rather than for individual words.
- SEO4 toolsSearch engine optimisation is the practice of making a site more likely to be found through organic search, covering technical crawlability, content relevance and external links.
- SHA-24 toolsSHA-2 is a family of cryptographic hash functions published by NIST, including SHA-256 and SHA-512. It is the family in general use today; SHA-1 and MD5 are considered broken for security purposes.
- Sitemaps2 toolsAn XML sitemap lists a site’s URLs with optional metadata such as last-modified date, helping search engines discover pages that internal linking alone might not surface.
- Snake case2 toolsSnake case joins words in lower case with underscores, as in background_color.
- Social media3 toolsSocial media are platforms on which users publish content and interact with each other’s posts.
- Speech recognition4 toolsSpeech recognition converts spoken audio into text. It is also called automatic speech recognition, or ASR.
- SQL6 toolsSQL (Structured Query Language) is the standard language for defining and querying data in relational databases. It is standardised by ISO/IEC 9075, though every database ships its own dialect.
- Stylometry2 toolsStylometry analyses measurable features of writing style — word and sentence lengths, vocabulary and function-word frequencies — usually to attribute or distinguish authorship.
- SubRip8 toolsSubRip (.srt) is a plain-text subtitle format. Each cue is a sequence number, a start and end timestamp, and one or more lines of text, separated by a blank line.
- Substitution cipher3 toolsA substitution cipher replaces each unit of plaintext with another according to a fixed rule. Simple versions preserve letter frequencies, which is what makes frequency analysis effective against them.
- SVG9 toolsSVG (Scalable Vector Graphics) is an XML-based format for two-dimensional vector graphics, standardised by the W3C. Because shapes are described mathematically rather than as pixels, they stay sharp at any size.
T
- Temperature2 toolsTemperature is a physical quantity expressing how hot or cold something is. The common scales are Celsius, Fahrenheit and the SI unit, the kelvin.
- Thumbnail2 toolsA thumbnail is a reduced-size copy of an image used as a preview, so many items can be scanned at once without loading each one at full resolution.
- Timesheet2 toolsA timesheet records the hours a person works, usually broken down by day and by task or project.
- Tokenization2 toolsTokenisation splits text into the units a model actually processes. For language models these are subword tokens, so token count does not match word count.
- TOML2 toolsTOML (Tom’s Obvious Minimal Language) is a configuration file format designed to map unambiguously to a hash table. It uses key/value pairs grouped under bracketed table headings.
- TOTP2 toolsA time-based one-time password is a short code derived from a shared secret and the current time, so it changes every interval — usually 30 seconds. It is the mechanism behind most authenticator apps.
- TrueType6 toolsTrueType is an outline font format developed by Apple and later adopted by Microsoft, describing glyphs with quadratic Bézier curves. Files usually carry the .ttf extension.
- Twitter Cards4 toolsTwitter Cards (now X Cards) are meta tags that control how a link is rendered when posted on the platform, selecting a layout such as summary or summary_large_image.
- TypeScript3 toolsTypeScript is a superset of JavaScript that adds static type annotations, checked at compile time and erased when the code is emitted as JavaScript. It is developed by Microsoft.
- Typography7 toolsTypography is the craft of arranging type — typeface, size, spacing, line length and hierarchy — so that text is readable and its structure is clear.
U
- Unicode12 toolsUnicode is the character encoding standard that assigns a unique code point to every character across the world’s writing systems, along with rules for their properties and behaviour. It is maintained by the Unicode Consortium.
- Unix time3 toolsUnix time counts the seconds elapsed since 00:00:00 UTC on 1 January 1970, ignoring leap seconds. It is the timestamp representation most systems store internally.
- URL4 toolsA URL is the address of a resource on the web. It combines a scheme, host, optional port, path, optional query string and optional fragment.
- URL redirection2 toolsURL redirection sends a client from one URL to another, usually with a 301 (permanent) or 302/307 (temporary) HTTP status and a Location header. Permanent redirects are what preserve a moved page’s search equity.
- US Letter2 toolsUS Letter is the paper size of 8.5 × 11 inches (216 × 279 mm), standard in the United States and Canada.
- User agent2 toolsThe User-Agent header is a string a browser sends identifying itself, its engine and its platform. Decades of compatibility workarounds have made the format largely fictional.
- UTC3 toolsCoordinated Universal Time is the primary time standard by which the world regulates clocks. Time zones are defined as offsets from it, and it does not observe daylight saving.
- UTF-162 toolsUTF-16 encodes Unicode code points in one or two 16-bit units, using surrogate pairs for characters above U+FFFF. It is the in-memory string representation used by JavaScript, Java and Windows.
- UTF-87 toolsUTF-8 is a variable-width encoding of Unicode using one to four bytes per code point. ASCII characters keep their single-byte values, which is why it became the dominant encoding on the web.
- UUID5 toolsA UUID (also called a GUID) is a 128-bit identifier designed to be unique without a central registry. Version 4 is random; version 7 embeds a timestamp so values sort chronologically.
V
- vCard5 toolsvCard is the standard file format for electronic contact cards, carrying names, phone numbers, addresses and photos. Version 4.0 is defined in RFC 6350.
- Vector database2 toolsA vector database stores embeddings and retrieves the nearest ones to a query vector, typically using approximate nearest-neighbour indexes.
- Version control2 toolsVersion control records changes to files over time, so any earlier state can be recovered and parallel work can be merged.
- Video editing2 toolsVideo editing is the selection and arrangement of video footage, with transitions, audio and effects, into a finished sequence.
W
- W3C6 toolsThe World Wide Web Consortium is the standards body that develops many of the web’s specifications, including CSS, SVG, WCAG and WebVTT. HTML and the DOM are now maintained by the WHATWG.
- WAV4 toolsWAV is an uncompressed audio container format from Microsoft and IBM, built on the RIFF structure. It stores raw PCM samples, so files are large but lose nothing.
- WCAG9 toolsThe Web Content Accessibility Guidelines are the W3C recommendations for making web content accessible, organised under four principles: perceivable, operable, understandable and robust. Success criteria are graded A, AA and AAA.
- Web browser2 toolsA web browser is the application that fetches web resources, renders HTML, CSS and images, and executes JavaScript.
- Web colors4 toolsWeb colours are the colour values CSS accepts: hex notation, rgb(), hsl(), the modern oklch() and lab() functions, and around 148 named keywords.
- Web crawler3 toolsA web crawler is a program that systematically fetches web pages and follows their links, typically to build a search index or a dataset.
- Web design3 toolsWeb design is the practice of planning and creating the visual appearance, structure and interaction of websites.
- Web layout2 toolsWeb layout is the arrangement of elements on a page. Modern CSS handles it primarily through flexbox for one-dimensional rows or columns and grid for two-dimensional structures.
- Web performance3 toolsWeb performance is how quickly and smoothly a page loads and responds. Google measures it publicly through the Core Web Vitals: LCP, INP and CLS.
- WebAssembly2 toolsWebAssembly is a portable binary instruction format that runs at near-native speed in browsers and other hosts. It lets code written in C, C++, Rust and similar languages run on the web.
- WebGPU8 toolsWebGPU is a W3C standard giving web pages access to GPU rendering and general-purpose compute. It replaces WebGL with an API modelled on modern graphics backends.
- WebKit2 toolsWebKit is the open-source browser engine developed primarily by Apple and used by Safari. Chrome’s Blink engine began as a fork of it.
- WebM3 toolsWebM is an open, royalty-free media container designed for the web, built on the Matroska structure and pairing VP8/VP9 or AV1 video with Vorbis or Opus audio.
- WebP5 toolsWebP is a raster image format developed by Google that supports both lossy and lossless compression, transparency and animation. It generally produces smaller files than JPEG or PNG at comparable quality.
- WebVTT7 toolsWebVTT (Web Video Text Tracks) is the W3C subtitle and caption format used by the HTML <track> element. Cues carry timestamps and optional positioning and styling settings.
- Well-formedness2 toolsWell-formedness is the requirement that a document obeys its format’s basic syntax rules — in XML, that every element is closed and correctly nested. It is weaker than validity, which also requires conformance to a schema.
- Whisper5 toolsWhisper is an open-source automatic speech recognition model released by OpenAI, trained on a large multilingual dataset and able to transcribe and translate speech.
- WOFF6 toolsWOFF (Web Open Font Format) is a W3C font format for the web: a TrueType or OpenType font wrapped in a container with zlib compression and metadata. It exists so fonts can be served efficiently rather than as raw desktop files.
- WOFF26 toolsWOFF2 is the second version of the Web Open Font Format, replacing WOFF’s zlib compression with Brotli. It typically produces files around 30% smaller than WOFF, and is the format browsers prefer.
- Word embedding2 toolsA word embedding maps words to dense vectors whose geometry reflects usage, so words appearing in similar contexts sit near each other.
X
- XLSX16 toolsXLSX is the Microsoft Excel workbook format introduced with Office 2007. It stores worksheets, formulas and styling as Office Open XML parts inside a ZIP archive.
- XML6 toolsXML (Extensible Markup Language) is a W3C markup language for encoding structured documents and data using nested, self-describing tags. It underpins formats including Office Open XML, SVG and RSS.
Y
Z
- Zero-width space3 toolsA zero-width space (U+200B) is an invisible Unicode character that marks a permitted line-break point without occupying width. Because it is invisible, it also turns up in text intended to defeat copy detection.
- ZIP6 toolsZIP is an archive format that stores multiple files and directories in one container, each compressed independently. It is the basis of several document formats, including Office Open XML and EPUB.
- Zod2 toolsZod is a TypeScript schema declaration and validation library. A schema defined once both validates data at runtime and produces the matching static TypeScript type.
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Definitions are written by hand rather than generated. Where a tool on this site cites the specification that defines a term, that citation is shown on the term's page. Terms we could not define from a source we trust are left out deliberately — an empty entry is better than a confident wrong one.