Base64 is a binary-to-text encoding scheme that represents binary data in an ASCII string format using 64 characters (A-Z, a-z, 0-9, +, /). It's widely used for embedding images directly in HTML/CSS, transmitting files via APIs (like REST or GraphQL), storing binary data in JSON, and sending email attachments via MIME. The main advantage is that Base64 ensures binary data remains intact during transport through systems that may not handle raw binary correctly.

Base64 encoding increases the data size by approximately 33% to 37%. This happens because every 3 bytes of binary data are encoded into 4 Base64 characters. For example, a 1 MB file becomes roughly 1.33 MB when Base64-encoded. Additionally, if you include the Data URI prefix (e.g., data:image/png;base64,...), there's a small extra overhead for the MIME type declaration. This tool shows you the exact size comparison after encoding.

Yes, absolutely. This tool performs all encoding and decoding entirely client-side in your browser using JavaScript's built-in FileReader and Base64 APIs. Your files are never uploaded to any server, transmitted over the network, or stored anywhere. The processing happens locally on your device. You can even disconnect your internet after loading the page and the tool will continue to work perfectly — this is a key advantage over server-based Base64 converters.

Plain Base64 is just the raw encoded string (e.g., iVBORw0KGgo...), suitable for API payloads and backend processing. A Data URI includes a prefix that specifies the MIME type and encoding (e.g., data:image/png;base64,iVBORw0KGgo...), allowing it to be used directly in HTML <img> tags, CSS backgrounds, or browser address bars. Our tool lets you toggle between both formats — enable "Include Data URI prefix" for web embedding, or disable it for API usage.

All file types are supported — images (PNG, JPEG, GIF, WebP, SVG), documents (PDF, DOCX, XLSX), archives (ZIP, RAR), audio, video, and any other binary format. There is no strict file size limit, but for practical performance, we recommend files under 100 MB. Larger files may cause browser slowdowns or memory issues. For very large files, consider using a command-line tool like base64 on Linux/macOS or certutil on Windows.

Switch to the "Decode Base64 → File" tab, paste your Base64 string, specify the output filename with the correct extension (e.g., photo.jpg, report.pdf), and click "Decode & Download". If your Base64 string includes a Data URI prefix, the file type will be auto-detected. The tool converts the Base64 back into binary and triggers a download of the reconstructed file — all locally in your browser.

Yes, Base64-encoded images with Data URI prefixes can be embedded directly in HTML emails and web pages using <img src="data:image/png;base64,...">. However, be aware that some email clients (especially older versions of Outlook) have limited support for Data URIs. For maximum email compatibility, traditional linked images (hosted on a server) are generally preferred. For web pages, Base64 embedding can reduce HTTP requests but may increase HTML file size and prevent browser caching of images.

Decoding can fail for several reasons: (1) The input contains invalid characters — valid Base64 only uses A-Z, a-z, 0-9, +, /, and = for padding. (2) The string is corrupted or truncated. (3) There are whitespace or line breaks that need trimming. (4) If using a Data URI, the prefix format is incorrect. Our tool automatically trims whitespace and handles Data URI parsing to minimize errors. If decoding fails, double-check your Base64 string for any extra characters or missing padding (=).