File types
What is this file, and how do I fix it?
Plain-English guides to 40 file formats developers and site owners deal with: what each one is, how to open it on any system, common problems and the File2fix tools that help.
Archives
7-Zip archive
A .7z file is an archive in the open 7z format created by 7-Zip. It usually compresses better than ZIP thanks to…
.gzGzip compressed file
A .gz file is a single file compressed with gzip. You meet it as rotated server logs (access.log.2.gz), compressed SQL…
.rarRAR archive
A .rar file is a compressed archive created with WinRAR, a proprietary format by Eugene Roshal. It is common for large…
.tar.gzTAR.GZ archive
A .tar.gz file, or tarball, is a TAR archive that has been compressed with gzip. It is the standard way to ship source…
.zipZIP archive
A .zip file is a compressed archive that bundles files and folders into one file, usually with DEFLATE compression. It…
Code
JavaScript file
A .js file contains JavaScript source code, the language that runs in web browsers and on servers through Node.js…
.phpPHP script
A .php file is plain-text source code written in PHP, the server-side language behind WordPress, Laravel, Drupal and a…
.pyPython script
A .py file is a Python source file: plain text that the Python interpreter runs as a script or imports as a module…
Data & config
CSV (comma-separated values) file
A .csv file is plain text where each line is a row and values are separated by commas (or sometimes semicolons or…
.envEnvironment variables (.env / dotenv) file
A .env file holds environment variables as KEY=value lines, such as database passwords, API keys and app settings…
.iniINI configuration file
An .ini file is a plain-text configuration file made of [sections] and key=value pairs. Developers meet it as php.ini…
.jsonJSON data file
A .json file stores structured data as JavaScript Object Notation: objects, arrays, strings, numbers, booleans and…
.ndjsonNewline-delimited JSON
An .ndjson file contains one complete JSON value per line, usually one object per record, separated by newlines. It is…
.tomlTOML configuration file
TOML (Tom's Obvious, Minimal Language) is a human-readable configuration format with INI-like [sections] and strict…
.tsvTab-separated values file
A .tsv file stores a table as plain text, with one row per line and columns separated by tab characters. It is common…
.xlsxExcel workbook
An .xlsx file is a Microsoft Excel workbook in the Office Open XML format, holding one or more sheets of cells…
.xmlXML document
An .xml file is a text document that structures data with nested tags, defined by the W3C Extensible Markup Language…
.yamlYAML file
A .yaml or .yml file is a human-readable configuration file that uses indentation to express structure. It powers…
Databases
Documents & text
Word document
A .docx file is a Microsoft Word document in the Office Open XML format, used by Word since 2007. It is the default…
.mdMarkdown document
A .md file is a plain-text document written in Markdown, a lightweight syntax where # makes headings, * makes lists…
.pdfPDF document
PDF (Portable Document Format) is a fixed-layout document format that looks the same on every device and printer. It…
.txtPlain text file
A .txt file holds plain, unformatted text with no fonts, images or layout. It is used for notes, README files, logs…
Images
GIF image
GIF (Graphics Interchange Format) is a 1987-era image format limited to 256 colours per frame, best known today for…
.icoICO icon file
An .ico file is a Windows icon container that can hold several images of different sizes in one file. On the web it is…
.jpgJPEG image
A .jpg file is a JPEG image, the most common format for photos from cameras, phones and the web. It uses lossy…
.pngPNG image
PNG (Portable Network Graphics) is a lossless image format with full transparency support. It is the standard for…
.svgSVG vector image
SVG (Scalable Vector Graphics) is an XML-based vector image format that stays sharp at any size. It is used for logos…
.webpWebP image
WebP is an image format from Google that supports lossy and lossless compression, transparency and animation in one…
Security & keys
X.509 certificate
A .crt file contains an X.509 digital certificate, most often the SSL/TLS certificate for a website or an…
.keyPrivate key file
On servers, a .key file usually holds the private key that pairs with an SSL/TLS certificate, created when you…
.pemPEM certificate or key file
A .pem file is a Base64 text container for cryptographic material: TLS certificates, certificate chains, private keys…
.pfxPKCS#12 certificate bundle
A .pfx file (also .p12) is a password-protected PKCS#12 bundle that packs a certificate, its private key and usually…
Web & server
Nginx configuration file
Nginx configuration files (nginx.conf plus site files ending in .conf) tell the Nginx web server how to listen, serve…
.cssCSS stylesheet
A .css file is a Cascading Style Sheets stylesheet that controls the colours, fonts, layout and animation of web…
.htaccessApache .htaccess file
A .htaccess file is a per-directory configuration file for the Apache web server (and LiteSpeed). Site owners use it…
.htmlHTML web page
An .html file is a web page written in HyperText Markup Language, the tag-based format browsers render. You meet it as…
.htpasswdApache password file
A .htpasswd file stores usernames and hashed passwords for HTTP Basic Authentication on Apache, and Nginx can read the…
.logLog file
A .log file is a plain-text record of events written by an application, web server or operating system, one entry per…