Reference Hub is a free online reference site for software developers. It contains 1,192 reference entries across 8 subject areas. Every entry includes descriptions, code examples, and usage notes. The data is sourced from official standards including IANA registries, RFC specifications, MDN Web Docs, ISO 3166, and W3C HTML specifications.
HTTP status codes are three-digit responses from a server indicating the result of a client request. Common codes include 200 (OK), 301 (Moved Permanently), 400 (Bad Request), 401 (Unauthorized), 403 (Forbidden), 404 (Not Found), 429 (Too Many Requests), and 500 (Internal Server Error). The HTTP status code reference covers all 85 standard status codes organized into five categories: 1xx informational, 2xx success, 3xx redirection, 4xx client errors, and 5xx server errors. Each status code entry includes the reason phrase, RFC reference, common causes, troubleshooting guidance, and example code snippets in multiple programming languages.
HTTP headers let the client and server pass additional information with HTTP requests and responses. This reference covers 133 standard HTTP headers organized by function: authentication (Authorization, WWW-Authenticate), caching (Cache-Control, ETag), CORS (Access-Control-Allow-Origin), security (Content-Security-Policy, Strict-Transport-Security, X-Frame-Options), cookies (Set-Cookie, Cookie), content negotiation (Accept, Content-Type), and more. Each header entry shows the header syntax, example values, and whether it is used in requests, responses, or both.
The ASCII table (American Standard Code for Information Interchange) is a character encoding standard for electronic communication. This reference covers all 256 ASCII codes from 0 to 255, including 33 control characters (NUL, SOH, STX, etc.), digits 0-9, uppercase and lowercase Latin letters A-Z and a-z, punctuation marks, and the extended ASCII characters (128-255) which include accented letters, currency symbols, mathematical operators, and typographic marks. Each entry shows the decimal, hexadecimal, binary, and octal values, the HTML entity, and keyboard shortcuts for control characters.
MIME types (Multipurpose Internet Mail Extensions) indicate the nature and format of a document or file. This reference covers 104 MIME types used on the web, organized into application (JSON, PDF, ZIP, XML), text (HTML, CSS, JavaScript, CSV), image (PNG, JPEG, GIF, SVG, WebP, AVIF), audio (MP3, WAV, OGG, FLAC, AAC), video (MP4, WebM, AVI, MOV), font (WOFF, WOFF2, TTF, OTF), and multipart types. Each entry shows the file extension and common usage scenarios.
HTML (HyperText Markup Language) uses tags to structure content on the web. This reference documents 115 HTML elements organized by category: document metadata (html, head, title, meta, link, style, script, base), sectioning (body, section, nav, article, aside, header, footer, main, address), text content (p, div, span, pre, blockquote, hr, br, wbr), inline text semantics (a, abbr, code, em, strong, mark, sub, sup, time, span), lists (ul, ol, li, dl, dt, dd), tables (table, thead, tbody, tr, th, td), forms (form, input, button, select, textarea, label, fieldset, progress, meter), and media (img, picture, video, audio, source, canvas, svg, iframe). Many entries include usage notes and an interactive live preview playground.
HTML entities are special codes used to display reserved characters, symbols, and special characters in HTML documents. This reference covers 252 HTML character entities including basic entities (ampersand &, less-than <, greater-than >, non-breaking space ), Latin accented letters (agrave, aacute, acirc, atilde, auml, aring, ccedil, egrave, eacute, etc.), Greek letters (Alpha through Omega, both uppercase and lowercase), mathematical symbols (summation, infinity, pi, integral, square root, approximately equal, not equal, plus-minus, division, multiplication), arrows (left, right, up, down, double arrows), currency symbols (euro, pound, yen, cent), and typographic marks (copyright, registered trademark, bullet, em dash, en dash, quotation marks). Each entry shows the entity code, numeric code, and rendered character.
ISO 3166-1 is a standard that defines two-letter codes for countries and dependent territories. This reference lists 249 country codes organized by continent: Africa (54 countries including South Africa ZA, Nigeria NG, Kenya KE, Egypt EG, Morocco MA), Asia (48 countries including China CN, India IN, Japan JP, South Korea KR, Saudi Arabia SA, Thailand TH, Vietnam VN, Indonesia ID), Europe (44 countries including United Kingdom GB, Germany DE, France FR, Italy IT, Spain ES, Netherlands NL, Switzerland CH), Americas (35 countries including United States US, Canada CA, Brazil BR, Mexico MX, Argentina AR), and Oceania (14 countries including Australia AU, New Zealand NZ, Fiji FJ). Each entry shows the two-letter ISO code, three-digit numeric code, and geographic region.
Cron is a time-based job scheduler in Unix-like operating systems. This reference covers the cron expression format which uses five fields: minute (0-59), hour (0-23), day of month (1-31), month (1-12), and day of week (0-7). It documents special characters including asterisk for any value, comma for lists, hyphen for ranges, forward slash for step values, and named presets like @yearly, @monthly, @weekly, @daily, @hourly, and @reboot. Includes 14 practical scheduling examples such as "every 5 minutes", "daily at midnight", "weekdays at 9 AM", "every Monday at 3 AM", "monthly on the 1st", and "twice daily".
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