ZIP to Base64

How to convert a ZIP to Base64

1. Drop a .zip file on the box or pick it with the file picker.
2. Output as starts on Plain Base64. Use JSON if you want the file name, type and size alongside, or HTML <a download> for a download link.
3. Leave Wrap at 76 off unless the string goes into a MIME email body.
4. Copy output, or Save as .txt for large archives.

Zip first, then encode

Base64 adds about a third to whatever you give it. Compression takes away from text, JSON, CSV, HTML and logs before that happens, so the order matters. A small test with a 219,398-byte JSON file, an HTML page and a stylesheet:

Images, videos, MP3s and existing archives are already compressed and barely shrink, but bundling them in a ZIP still turns many files into one field. For a single text payload, gzip is a lighter option; see Gzip and Base64.

Where Base64 ZIPs are used

• Deployment and automation APIs: some services that run code or host sites accept the whole package as a Base64-encoded ZIP inside a JSON request.
• CI and secret stores: a folder of certificates or config files can be zipped and stored as one Base64 secret, then restored in the pipeline with base64 -d.
• Bulk exports and attachments: a set of reports or invoices goes out in one request instead of one field per file.

Building the ZIP in code

Python can create the archive in memory and encode it without writing a temporary file:

import base64, io, zipfile
from pathlib import Path

buf = io.BytesIO()
with zipfile.ZipFile(buf, "w", zipfile.ZIP_DEFLATED) as z:
    for path in Path("site").rglob("*"):
        if path.is_file():
            z.write(path, path.relative_to("site"))

package = base64.b64encode(buf.getvalue()).decode("ascii")

ZIP_DEFLATED matters: the default ZIP_STORED does not compress at all. More on streaming and line endings in Base64 in Python.

Checking a Base64 ZIP

If the string starts with UEsFBg, the archive was created with no files, a frequent result of a wrong path in a build script. Base64 to ZIP decodes a string and lists the files inside, which is the quickest way to check that the archive contains what you expect.

FAQ