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Base64 Encoder / Decoder — Free Online Tool
Encode text or files to Base64, or decode Base64 strings back to text or files. Supports URL-safe Base64. No signup, runs in your browser.
Everything runs in your browser. Your text and files are never uploaded or stored.
Input — Text
Output
Output will appear here.
About Base64 Encoder / Decoder
Base64 Encoder / Decoder is a free browser-based tool that converts text or files to Base64 and decodes Base64 strings back to their original form. Everything runs locally in your browser — no data is uploaded or stored. The tool supports standard Base64 (RFC 4648) and URL-safe Base64, and can encode any file up to 5 MB.
Common use cases
- Inspect or construct JWT tokens — decode the header and payload segments, or encode a custom payload for testing.
- Encode images or fonts as Base64 data URIs for embedding directly in HTML or CSS without extra HTTP requests.
- Convert API keys, credentials, or binary data to a safe text format for embedding in JSON fields or HTTP headers.
- Decode Base64-encoded email attachments (MIME) to check their content without downloading them.
- Generate URL-safe Base64 tokens for use in query strings, OAuth state parameters, or short-lived links.
Frequently asked questions
What is Base64 encoding?
Base64 is a binary-to-text encoding scheme that represents binary data using 64 printable ASCII characters (A–Z, a–z, 0–9, +, /). It is used to safely transmit binary data — images, files, cryptographic keys — through text-only channels such as email bodies, JSON fields, and HTTP headers. The encoded output is approximately 33% larger than the original.
What is URL-safe Base64?
Standard Base64 uses + and / characters, which have special meanings in URLs and query strings. URL-safe Base64 (RFC 4648 §5) replaces + with - and / with _, and optionally strips the = padding characters. Use URL-safe Base64 for data embedded in URLs, JWT tokens, and web API parameters.
Does this tool send my data to a server?
No. All encoding and decoding runs entirely in your browser using JavaScript's built-in btoa() and atob() functions. Files are read locally via the FileReader API. Nothing is uploaded or stored.
Why does my Base64 output end with == or =?
Base64 encodes every 3 bytes of input as 4 characters. When the input length is not a multiple of 3, padding characters (=) are added. One trailing = means 1 byte of padding; two == means 2 bytes. Enable the URL-safe toggle to strip padding.
Can I decode a Base64 image back to a viewable image?
Yes. Paste the Base64 string into Decode mode and click Decode. The tool detects PNG, JPEG, GIF, and WebP by their magic bytes and shows a live preview plus a download button.
What is the 5 MB file size limit for encoding?
Base64 encoding expands data by roughly 33% — a 5 MB file becomes ~6.7 MB of Base64 text. The cap keeps output manageable in a browser textarea. For larger files, use `base64 -i file -o file.b64` on macOS/Linux or `certutil -encode file file.b64` on Windows.
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