Base64 Decoder Online

Decode Base64 strings back to original text and binary data — instant browser-based decoding

What Is Base64 Decoding?

Base64 decoding reverses Base64 encoding by converting an ASCII string of 64-character alphabet back into the original binary or text data. When you receive a Base64-encoded string from an API response, email attachment, data URI, or authentication header, decoding it reveals the original content — whether that is plain text, an image, a PDF, or any other binary format.

Decoding is essential for debugging API integrations where payloads are Base64-encoded, inspecting JWT token payloads (which use Base64URL encoding), extracting embedded images from HTML data URIs, reading email attachments encoded with MIME Base64, and generally recovering the original data from any Base64-encoded source. The decoding process is deterministic and lossless — valid Base64 always decodes to exactly the original bytes.

How to Decode Base64 Online

1. Paste your Base64-encoded string into the input field
2. Click Decode to convert it back to the original content
3. View the decoded text in the output panel
4. For binary content (images, files), use the download option to save the decoded file
5. Toggle between text and hex views to inspect non-printable characters

Why Use PinusX for Base64 Decoding?

PinusX decodes Base64 with 100% client-side processing in your browser. Your encoded data never leaves your device, which is critical because Base64-encoded content frequently contains sensitive information: authentication tokens (HTTP Basic Auth encodes username:password in Base64), JWT payloads with user claims, encrypted data wrapped in Base64 for transport, and private binary files. In November 2025, jsonformatter.org exposed over 80,000 user credentials that had been processed on their servers. PinusX avoids this completely — decoding runs locally in your browser tab, and no data is ever transmitted to any external server.

Frequently Asked Questions

How do I know if a string is Base64 encoded?

Base64 strings contain only characters from the set A-Z, a-z, 0-9, +, / and end with zero, one, or two = padding characters. The string length is always a multiple of 4. However, short strings may coincidentally match this pattern, so context matters — check if the source typically uses Base64 encoding.

Can I decode Base64URL format?

Yes. Our decoder handles both standard Base64 (with + and /) and Base64URL (with - and _). It auto-detects which variant is used based on the characters present in the input string. This means you can paste JWT token segments directly and decode them without manual conversion.

What if the Base64 string is invalid?

The decoder reports an error if the input contains characters outside the Base64 alphabet or has incorrect padding. Common issues include extra whitespace, line breaks from email formatting, or truncated strings. The error message indicates what the problem is so you can fix the input.

Can I decode Base64 to an image?

Yes. If the Base64 string represents an image (PNG, JPEG, GIF, SVG, WebP), the decoder detects the image format from the decoded bytes and displays a preview. You can then download the image file directly. This is useful for extracting images from data URIs in HTML or CSS.

Does decoding handle line breaks in Base64?

Yes. Many systems (especially email) insert line breaks every 76 characters in Base64 output per the MIME specification. Our decoder strips whitespace and line breaks before decoding, so you can paste Base64 with or without line wrapping and get correct results.

Your data never leaves your browser. 100% client-side processing.