How do I convert Base62 back to a file?

Paste the Base62-encoded string into the input field. The tool will automatically decode it to binary data, processing each Base62 character (0-9, A-Z, a-z) according to the case-sensitive Base62 alphabet where uppercase and lowercase letters represent different values. Then, enter the filename with the correct file extension (e.g., "image.png", "document.pdf", "archive.zip") and click Download. The browser will save the decoded file to your downloads folder. The file will be byte-for-byte identical to the original file that was encoded. Make sure you paste the complete Base62 string with exact capitalization—Base62 is case-sensitive, so "A" and "a" decode to different values, and any character change will corrupt the output.

Why is the filename and extension important for Base62 decoding?

Base62 encoding only preserves the binary data, not the filename or file type metadata. When you decode Base62 to a file, you must manually specify both the filename and extension because the decoder cannot recover the original filename from the encoded string. The file extension is critical—it tells your operating system which application should open the file. For example, use ".png" for PNG images, ".pdf" for PDF documents, ".zip" for archives, ".mp3" for audio, ".docx" for Word documents, etc. Using the wrong extension will not corrupt the data itself, but the file may not open correctly. If you forgot the original extension, you can identify the file type by looking at the first few Base62 characters which encode the file signature (magic numbers).

What does the character count mean in Base62 decoding?

The character count shows how many Base62 characters are in your input string. Since Base62 encoding increases file size by approximately 35%, you can estimate the original file size by calculating: original size ≈ (character count × log₂(62)) / 8 bytes. For practical purposes, every 1,000 Base62 characters represents roughly 740 bytes of original data. A 10KB file produces about 13,500 Base62 characters, while a 100KB file produces about 135,000 characters. If your character count seems much lower than expected for the file size you are trying to recover, the Base62 string is likely truncated or incomplete, which will result in a corrupted or partial file. Always verify you have the complete Base62 string before decoding.

Can I preview images before downloading from Base62?

Yes! If the decoded Base62 data represents an image file (JPEG, PNG, GIF, WebP, BMP, etc.), the tool automatically detects the image signature and displays a preview. This preview is generated directly from the decoded binary data, allowing you to visually verify the decoding was successful before downloading the file. The preview appears as soon as the Base62 string is decoded. If you expect an image but no preview appears, the Base62 string may be incomplete, corrupted, or may not actually represent an image file. The preview feature works for all common image formats and even shows transparency for PNG images. Once you confirm the preview looks correct, you can download the file with confidence that the decoding succeeded.

How do I calculate the expected file size from Base62?

To calculate the expected decoded file size from a Base62 string, use this formula: file size in bytes = (Base62 character count × log₂(62)) / 8, which simplifies to approximately character count × 0.74. For example, a Base62 string with 13,500 characters will decode to approximately 10,000 bytes (10 KB). This is because Base62 encoding represents data more efficiently than text—each Base62 character (using 62 possible values) encodes about 5.95 bits of data. The tool displays the calculated file size automatically after decoding. Compare this to the original file size you expect. If they match, the Base62 string is complete. If the decoded size is smaller, the string was truncated. If larger, extra characters were added, corrupting the data.

What happens if my Base62 string has invalid characters?

Base62 uses only alphanumeric characters: digits 0-9, uppercase letters A-Z, and lowercase letters a-z (total of 62 characters). If your Base62 string contains any character outside this set—such as spaces, punctuation, special characters like +/=, or non-Latin characters—the decoder will show an error identifying the invalid character. Common invalid characters include: spaces (often accidentally copied), plus signs and slashes (from Base64 confusion), equals signs (Base64 padding), hyphens, underscores, or line breaks. Before decoding, ensure your string contains only 0-9, A-Z, and a-z. The decoder is case-sensitive, so "A" and "a" are both valid but represent different values. Remove any formatting, whitespace, or separators that may have been added for readability.

Can I decode partial Base62 strings?

While you can technically decode a partial Base62 string, the result will be an incomplete and likely corrupted file that cannot be opened or used properly. Base62 encoding processes the entire file as a continuous stream of data, so missing even the last few characters means the end of the file is truncated. For text files, you might recover some readable content from a partial decode. For binary files like images, PDFs, or executables, partial decoding almost always produces unusable files because these formats require complete data structures and often include important metadata at the end of the file. If your Base62 string was truncated due to display limits, character count restrictions, or copy-paste errors, you must obtain the complete string. Look for "Download Full Text" or "Copy All" options in the encoding tool.

How can I detect the file type from a Base62 string?

You can identify the file type by decoding the first portion of the Base62 string and examining the file signature (magic numbers). Different file types start with distinctive byte patterns: JPEG images start with bytes FF D8 FF (often appearing as specific Base62 sequences at the start); PNG images start with 89 50 4E 47 (the PNG signature); PDF documents start with 25 50 44 46 (which is "%PDF" in ASCII); ZIP archives start with 50 4B 03 04; GIF images start with 47 49 46 38 ("GIF8"). After decoding, the tool may show a preview for image types. For other files, you can decode a small portion and use online file signature databases to identify the type. However, the most reliable method is to remember or document the file extension when encoding. Once identified, use the correct extension when downloading to ensure your system recognizes the file type.

Why does my decoded file appear corrupted?

File corruption after Base62 decoding typically occurs due to: incomplete Base62 string (missing characters at the beginning, middle, or end); case sensitivity errors (Base62 is case-sensitive, so changing "A" to "a" corrupts data); invalid characters accidentally included in the string; wrong character encoding when copying the Base62 string (some systems may transform characters); or the Base62 string was not generated correctly in the first place. To troubleshoot, first verify the character count matches expectations for the file size. Second, ensure all characters are valid Base62 (0-9, A-Z, a-z only). Third, confirm you have preserved exact capitalization. Fourth, try opening the file with different applications or using a hex editor to examine the file signature. If the first few bytes match the expected file type signature but the file will not open, the corruption likely occurred in the middle or end of the Base62 string.

Is decoding Base62 to files safe and private?

Yes, completely safe and private! All Base62 decoding happens entirely in your browser using client-side JavaScript. The Base62 string is decoded locally on your device, and the resulting file is created in browser memory. Nothing is uploaded to any server, transmitted over the internet, or stored anywhere except temporarily in your browser. This client-side processing ensures complete privacy—even the most sensitive files (financial documents, personal photos, medical records, proprietary business data, encryption keys) can be safely decoded without leaving your device. The tool works even when offline or with network disabled. Once you close the browser tab or refresh the page, all data is immediately cleared from memory. However, remember that Base62 encoding does not encrypt data—anyone with the Base62 string can decode it just as easily. Keep Base62-encoded sensitive data secure and never share Base62 strings of confidential files in public places.

Base62 to File Decoder Online

Decode Base62 strings back to original files instantly. Convert Base62 to images, PDFs, documents, or any file type. 100% free, secure, case-sensitive decoding in your browser.

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