Base64 File Extractor

Base64 is a binary-to-text encoding scheme that represents binary data in an ASCII string format using 64 printable characters (A-Z, a-z, 0-9, +, /). Each Base64 character encodes 6 bits of data, so every 3 bytes of binary data (24 bits) are encoded as 4 Base64 characters. This encoding increases the data size by approximately 33% (4 output characters for every 3 input bytes). Base64 is widely used for embedding binary data in text-based formats that cannot handle raw bytes - email attachments (MIME), data URIs in HTML/CSS, JSON API responses storing images or documents, XML data with binary content, and database fields storing small files. The encoding usespadding with = characters at the end when the input length is not a multiple of 3 bytes. A data URI format like data:image/png;base64,iVBOR...combines a MIME type declaration with the Base64 data in a single string, commonly used for embedding images directly in HTML or CSS.

• What are magic bytes? Magic bytes (also called file signatures or magic numbers) are specific byte sequences at the beginning of a file that identify its format. They are written by the application that created the file and are checked by operating systems and applications to determine file type when the extension is missing or incorrect. Magic bytes are far more reliable than file extensions for identifying file types.
• How the detection works: After decoding Base64 back to binary, the tool reads the first 16 bytes and converts them to a hexadecimal string. It then compares this string against a database of 30+ known file signatures, sorted by signature length (longer signatures match first for higher accuracy). Each signature specifies an optional byte offset, allowing detection of formats like MP4 where the signature starts at byte 4 rather than byte 0.
• What happens when no signature matches: If the decoded bytes don't match any known file signature, the tool reports "Unknown File Type" with a generic MIME type (application/octet-stream) and the .bin extension. The file can still be downloaded and opened, but the correct extension may need to be determined manually by inspecting the file in a hex editor or by the application that expects it.
• Limitations of magic byte detection: Magic byte detection is not infallible. Polyglot files can have valid signatures for multiple formats, some formats don't have unique signatures, and corrupted files may have damaged headers. The tool's database covers the most common 30+ formats, but doesn't include every file format in existence. For comprehensive detection, use our dedicated File Magic Byte Detector tool with 120+ signatures.

1. Paste or upload Base64 data: Switch to "Paste Base64" mode to type or paste your Base64 string directly into the text area. You can also drag and drop a .txt file containing Base64 onto the text area. Switch to "Upload File" mode to select a Base64 file from your device using the file browser. The tool accepts raw Base64 strings, data URIs (data:image/png;base64,...), and Base64 with or without line breaks and whitespace.
2. Click "Decode & Extract": The tool validates the Base64 input for correct characters and padding, then decodes it using the browser's atob() function. It strips data URI prefixes automatically, removes all whitespace, and validates the character set. If the input is invalid, a descriptive error message explains the issue and suggests how to fix it.
3. Review the detection results: The results panel shows the detected file type (with icon), the MIME type, the suggested file extension, the decoded file size, and a hex dump of the first 64 bytes. The hex dump is displayed in a classic three-column format with offset addresses, hex byte values, and ASCII interpretation, allowing you to visually verify the file signature.
4. Download the decoded file: Click the "Download File" button to save the decoded binary as a file with the correct extension. The file is generated as a Blob and downloaded directly through your browser - no server storage, no data transfer, completely private. The green download button provides immediate access to your extracted file.

Our Base64 File Extractor processes everything locally in your browser. Base64 decoding uses the native atob() function, and file type detection reads decoded bytes from typed arrays in memory. No data is ever uploaded to any server. The tool is 100% free with no signup, no account, and no usage limits.

Important limitations: The maximum decoded file size is approximately 100 MB (limited by browser memory). Files larger than this may cause the browser tab to crash. The magic byte database covers 30+ common file signatures - uncommon or proprietary formats may not be detected. Base64 input that is itself encoded within another format (e.g., Base64 inside JSON inside XML) must be extracted to the Base64 layer first. Encrypted or password-protected files are identified by their type but cannot be opened without the decryption key.

Best practices: Copy the complete Base64 string including any padding (= characters) at the end. For data URIs, copy the entire URI including the data: prefix. When extracting from emails, look for the Base64 block between boundary markers after the Content-Transfer-Encoding: base64 header. For large files, consider splitting them into smaller chunks or using a dedicated desktop tool for better performance. Always verify the downloaded file opens correctly, especially if the file type was detected as "Unknown".