Base64 Preview

A Visual Studio Code extension for seeing what a piece of Base64 actually is. Copy some Base64, paste it, or select it in the editor, and the panel decodes it, works out what it contains — text, JSON, an image, a PDF, an archive, a font — and shows it in the most useful way it can. Whatever it is, you can save it as a real file with the right extension, without anything leaving your machine.

Privacy

No telemetry. No network requests. Nothing you paste is stored. The clipboard is read only when you run a command, and never written to unless you press a copy button. Files are written only where you choose in the save dialog.

Decoding and file-type detection run entirely on your machine. See SECURITY.md for the full scope.

Features

• Live decoding as you type or paste.
• Picks up Base64 straight from the clipboard or the editor selection.
• Accepts bare Base64, data: URIs, the URL-safe alphabet, line-wrapped text, quoted strings and missing padding — and explains what is wrong when the text is not Base64 at all.
• Recognises what the bytes are from their signature: PNG, JPEG, GIF, WebP, SVG, BMP, ICO, AVIF, PDF, ZIP, DOCX, XLSX, PPTX, JAR, GZIP, 7z, RAR, TAR, MP3, WAV, OGG, FLAC, MP4, WebM, WOFF, TTF, OTF, SQLite, WebAssembly and more — and tells UTF-8 text, JSON, XML, HTML, PEM and JWTs apart from binary data.
• Shows the content in the most useful form: images inline, JSON as a collapsible tree, text as text, and everything else as a hex dump.
• Save as file… writes the decoded bytes to disk with a suggested name and extension that match the detected type, so a decoded docx opens in Word and a decoded png opens in an image viewer.
• Open in editor puts decoded text into a new editor tab with the right language mode; Copy text puts it on the clipboard.
• Flags a data: URI whose declared media type does not match the bytes.
• Follows the editor theme (light, dark, high contrast).

How detection works

The decoded bytes are matched against the leading bytes ("magic numbers") of well-known formats first. If none match, the bytes are decoded as UTF-8 (or as UTF-16 when a byte order mark is present); text that decodes cleanly is then classified by its content — JSON, SVG, HTML, XML, PEM, RTF, or a JWT — and otherwise treated as plain text. A data: URI's media type is used to refine a generic result (for example text/csv) but never to override what the bytes themselves say. Bytes that are neither text nor a known format are shown as "Binary data" with a hex dump, and can still be saved with a .bin extension.

Formats that have no inline preview in VS Code — PDFs, archives, Office documents, audio, video — are identified and can be saved; open the saved file in a suitable application.

Usage

Copy some Base64, open the Command Palette (Ctrl/Cmd+Shift+P), and run Base64: Open Preview. If the clipboard holds something shaped like Base64 or a data: URI, it is decoded straight away; otherwise paste it into the input field.

To decode Base64 that is already in your editor: select it, right-click, and choose Base64: Decode Selection. With nothing selected, this command falls back to the clipboard as well.

Use the Preview / Hex toggle to switch between the rendered view and the raw bytes. Press Save as file… to write the decoded content to disk; the save dialog suggests a file name with the detected extension.

If the decoded text turns out to be a JSON Web Token, the companion JWT Preview extension shows its claims in detail.

Installation

Install "Base64 Preview" from the Visual Studio Code Marketplace, or download a .vsix from the repository's Releases page and install it via Extensions: Install from VSIX....

Feedback and security

• Bugs and feature requests: GitHub Issues
• Security issues: see SECURITY.md — please never include real data in reports.

License

MIT — see also the changelog.