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Reference

File Format Guides

Plain-English guides to the file formats you work with every day: what each one is for, where it falls short, and the free browser tools that read and write it.

How to choose a format

Start from the job, not the extension. If another system must read the file unchanged, pick the format that system already accepts. If you are the only reader, pick the one that keeps the detail you still need.

For photographs, JPG and WebP trade some detail for a smaller file. PNG keeps every pixel and can carry transparency, so it suits screenshots, logos, and graphics with flat colour. Converting a JPG to PNG does not recover detail the JPG already discarded.

For documents that must look the same on every device, PDF fixes the layout. For tables you will sort or join, CSV stays flat and simple. For nested records an API will parse, JSON keeps the structure. Markdown is for notes you want to read as text and render later.

Each guide below says what the format is good at, where it gets in the way, and which tool on this site reads or writes it. Open the guide before you convert, so the output matches the next step rather than only the file name.

data formats

.jsonJSON A lightweight, text-based format for structured data built from objects, arrays and primitives..xmlXML A tag-based markup format for structured documents and data with attributes, namespaces and schemas..csvCSV A flat, row-and-column text format where each line is a record and fields are separated by a delimiter..yamlYAML An indentation-based data format designed to be comfortable for humans to read and edit.

image formats

.pngPNG A lossless raster image format with full alpha transparency..jpgJPG A lossy raster format tuned for photographs, with adjustable quality..webpWebP A modern image format offering both lossy and lossless modes plus transparency..svgSVG An XML-based vector format that scales to any size without losing sharpness.

document formats

.mdMarkdown A plain-text writing format that converts predictably to HTML..pdfPDF A fixed-layout document format that renders identically on every device..docxDOCX The Microsoft Word document format — a zipped bundle of XML parts..xlsxXLSX The Excel workbook format, with multiple sheets, formulas and formatting..zipZIP A compressed archive that bundles a folder tree into one file.

encoding formats

.txtBase64 An encoding that represents binary data using 64 printable ASCII characters..txtJWT A signed, Base64URL-encoded token carrying JSON claims..txtUUID A 128-bit identifier that can be generated independently without collisions..txtURL The escaping rules that let arbitrary text travel safely inside a URL.

code formats

.sqlSQL The declarative query language used to read and modify relational databases..txtCron A five- or six-field syntax describing when a recurring job should run..txtRegex A pattern language for matching, extracting and replacing text..tsTypeScript Typed JavaScript — interfaces and types that describe the shape of runtime data.