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Base64 Decoder

Runs in browser

Decode Base64 or Base64URL strings to plain text or download as a binary file. Handles MIME line-wrapping and PEM certificates automatically.

Last updated 02 Apr 2026

Paste a Base64 or Base64URL string to instantly decode it back to plain text. Switch to File mode to download the decoded bytes as a binary file. Handles MIME/PEM line-wrapped input, URL-safe alphabet, and missing padding. Runs entirely in your browser — nothing is uploaded.

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How to use

  1. 1

    Paste your Base64 string

    Paste the Base64 or Base64URL string into the input field. Multi-line MIME or PEM-wrapped input is automatically cleaned up — no manual reformatting needed.

  2. 2

    Select Standard or URL-safe mode

    Choose URL-safe mode if your string uses - and _ instead of + and /, or if it comes from a JWT token or OAuth parameter. Missing padding is added automatically.

  3. 3

    Read the decoded output

    The decoded text appears in the output panel in real time. If the Base64 is invalid, a clear error message indicates the problem.

  4. 4

    Copy or download the result

    Click Copy to copy the decoded text to your clipboard. For binary data, switch to File mode and click Download to save the raw bytes as a file.

Frequently asked questions

Why do I get a decoding error?
The most common causes are: invalid characters outside the Base64 alphabet, incorrect string length (must be a multiple of 4 for standard Base64), or using standard mode for a Base64URL string. Switch to URL-safe mode if your string uses - and _ instead of + and /.
Can I decode Base64 spread across multiple lines?
Yes. The decoder strips all whitespace (spaces, newlines, tabs) before decoding. MIME-formatted Base64 (76 chars per line) and PEM certificate blocks both decode correctly without any preprocessing.
Is this tool safe to use? Are inputs sent to a server?
No data is uploaded. All decoding runs client-side in your browser using the atob() function and the TextDecoder API. Nothing leaves your device.
How do I decode a Base64-encoded file?
Switch to File mode using the File tab. Paste the Base64 string, then click Download Decoded File to save the raw bytes. The file is created entirely in your browser — no server is involved.
What is Base64URL and when do I use it?
Base64URL is the URL-safe variant of Base64 (RFC 4648 §5). It replaces + with - and / with _, and omits = padding. It is used in JWT tokens, OAuth 2.0 parameters, and any context where + and / would require percent-encoding in a URL.
What happens if the decoded output is binary data?
In text mode the output is decoded via TextDecoder. Binary content (images, PDFs) may render as garbled characters — use File mode to save binary payloads as a downloadable file instead.
Can I decode a data URI with this tool?
Yes. Paste the full data URI (e.g. data:image/png;base64,...) and the decoder will strip the prefix and decode the Base64 payload. Use File mode to download the result as a file.
What is the difference between Base64 and Base64URL?
Standard Base64 uses + and / in its alphabet and = for padding. Base64URL replaces + with - and / with _, and typically omits the = padding. Standard Base64 is safe in most contexts; Base64URL is specifically designed for safe embedding in URLs and HTTP headers without percent-encoding.
Why does my decoded text look garbled?
If the decoded text looks garbled, either you are trying to decode binary data as text (use File mode instead), the encoding is Base64URL but you selected Standard mode, or the input is not actually Base64-encoded.

Decode Base64 or Base64URL strings back to human-readable text or raw

binary files, entirely in your browser.

**Text decode:** Paste any Base64 string — including MIME-wrapped (76 chars

per line) and PEM certificate blocks — and get the original UTF-8 text

instantly. Whitespace and newlines are stripped automatically so copy-pasted

multi-line Base64 works without manual cleanup.

**Base64URL decode:** Toggle URL-safe mode to handle tokens where `+` is

replaced by `-` and `/` by `_`. Missing `=` padding is restored automatically.

Use this for JWT tokens, OAuth state parameters, and URL-embedded data.

**File decode:** Switch to File mode, paste a Base64 string, and click

Download to save the raw bytes as a file. Recover images, PDFs, or binary

data embedded in JSON payloads or data URIs.

**Data URI decode:** Paste a full `data:image/png;base64,...` URI to extract

and download the embedded file directly.

Character and byte counts are displayed below the output. All processing

is client-side — your data never leaves your device.

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