Nothing is uploaded. When you drop, browse, paste or fetch a file the encoder reads it locally with the browser’s File API and converts it to Base64 in memory on your device using JavaScript, in small chunks so even large files do not lock up the tab. There is no server, API, database or tracking in the processing path, so a private document, screenshot, certificate or any other sensitive file stays on your machine. The tool works offline once cached, and closing the tab discards everything. The one case where data touches the network is if you paste a remote URL for the tool to fetch — and even then the response is downloaded straight into your browser and never sent anywhere else. The only optional network use anywhere on the site is consent-gated advertising, which never sees your file.

Plain Base64 is the bare payload — the A–Z, a–z, 0–9, + / characters that represent your file’s bytes — which you would decode back to a file or drop into a JSON field. A data URI wraps that payload with a scheme and MIME type, like data:image/png;base64,iVBORw0KGgo…, so a browser treats the whole string as an inline resource and renders it with no extra request. This encoder builds the data URI for you and detects the MIME type from the file’s magic numbers, and it can go further — wrapping the data URI in a ready-to-paste <img> tag, a download <a> anchor, a CSS background url(), a JSON object, an XML element or Markdown image syntax — so you copy exactly the snippet your code needs.

The standard Base64 alphabet uses + and /, which have special meaning in URLs and are illegal in filenames, so the URL-safe base64url variant swaps them for - and _; choose it whenever the string is going into a query parameter, path, cookie or filename. The = padding at the end is required by some parsers and rejected by others, so a toggle lets you keep or strip it. Line wrapping inserts a newline every N characters: 64 characters matches the PEM format used for certificates and keys, and 76 characters matches classic MIME email encoding, while “none” keeps one long line for embedding in code or a data URI. Defaults are the standard alphabet, padding on and no wrapping, which suits most web and data-URI use.

Switch to the Decode tab and paste raw Base64, a full data: URI, or even an HTML <img src=…> or CSS url(…) snippet — the tool auto-strips the prefix, whitespace and quotes, converts URL-safe characters back, re-pads the string and rebuilds the original bytes. It sniffs the MIME type and shows a live preview appropriate to the file: an image, an embedded PDF, an audio or video player, decoded text, or a hex dump for binary formats, with a one-click download. On the encode side you can process many files at once, each with its own progress bar, and there is a 500 MB per-file limit because everything is held in browser memory; remember that Base64 inflates size by about a third, so very large files are better handled as normal downloads than embedded as data URIs.