Converters

Base64 File Converter

Encode a local binary file as Base64 or recover bytes as a download. Check input limits, padding, filenames, and why binary data differs from UTF-8 text.

Local processing

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About this tool

When to use it

Encode a local binary file as Base64 or recover bytes as a download. Check input limits, padding, filenames, and why binary data differs from UTF-8 text.

How to use it

Choose File to Base64 and select a nonempty local file. Copy the encoded text or download a .base64.txt file. To recover bytes, switch to Base64 to file, paste the Base64 text, choose the original filename and extension, then select Decode and download. Switching modes clears the workspace. A filename labels the bytes; it does not convert their format.

Guide updated 2026-09-15. Examples checked against this implementation.

Worked examples

Recover a small text fixture

Input

SGVsbG8=
Download filename: greeting.txt

Expected output

Hello

The downloaded file contains five bytes, with no trailing newline. Selecting that file in File to Base64 produces SGVsbG8= again.

Preserve bytes that are not text

Input

AP8B
Download filename: fixture.bin

Expected output

Hexadecimal bytes: 00 FF 01

The download contains exactly three bytes. It is not a UTF-8 string; use this file workspace rather than the text Base64 decoder.

Errors and unsupported input

data:image/png;base64,iVBORw0KGgo=

Remove the data URL prefix and supply only its Base64 portion. This sample is just a PNG signature, not a complete image; obtain the full source before downloading.

a=== or _w==

Use complete standard Base64 with + and / and valid padding. Base64URL uses a different alphabet. Do not guess missing bytes from a truncated value.

An empty file or a file larger than 5 MiB

Select a nonempty file up to 5,242,880 bytes. A rejected selection clears the old encoded result so it cannot be mistaken for the new file.

Continue this workflow

Base64 Encoder & Decoder: Encode and decode readable UTF-8 text directly without a file download.
JWT Parser: Inspect a complete JWT whose segments use Base64URL.

Format references

Base64 encoding format (RFC 4648)

Format rules and limitations

File encoding accepts up to 5 MiB. Base64 decoding accepts up to 7 MiB of UTF-8 input, including whitespace; decoded bytes may be slightly larger than the file-encoding limit.

The decoder accepts whitespace and valid omitted padding. It accepts standard Base64, not Base64URL, data URL prefixes, or MIME message headers.

Encoding stores bytes only: the original filename, MIME type, and file permissions are not embedded. Changing the download extension does not change the content.

Base64 provides no encryption or malware scanning. Downloading does not establish that a file is safe to open.

Privacy and security

These tools process input in browser memory without an upload or processing API. DevMate does not save these inputs in localStorage, sessionStorage, or a share URL. Reloading starts a new workspace; browser history restoration may retain form state. Copy writes to your system clipboard and Download saves a file, which can outlive the tab. The page still loads site assets and may contact configured analytics, consent, or advertising services. DevMate analytics records route and action names, without input, output, filenames, or raw errors.

Review sensitive or production-critical output in the trusted system where it will be used.

Questions

Frequently asked questions

Why does the Base64 text look larger than the original file?

Three source bytes become four Base64 characters, with padding for a partial final group. The output therefore needs roughly one third more space.

Will a .png filename turn arbitrary bytes into an image?

No. Recover the complete original image bytes and choose its matching extension. This tool does not transcode or repair files.