Base64 Encoder / Decoder

The most feature-complete base64 encoder decoder online: encode and decode in four variants (Standard, Base64URL, MIME, No-Padding), auto-detect content (images, JWT, JSON, URL), preview Base64 images in the browser, and scan for secrets — all without sending data to any server.

Paste text or Base64, use ?data=... in the URL to load, or drag a file in File mode. Runs fully in your browser.

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Runs fully in browserNo data leaves your devicePrivacy-first
0 opsInput 0 B
Input — Plain text

0 chars · 0 B

⌘Enter
Output — Base64
0 B output

⌘Enter process · ⌘⇧C copy · ⌘⇧X swap · ⌘K clear

JWT DecoderPassword Generator

Features

Encode plain text to Base64 and decode Base64 to text in one click. Choose Standard (RFC 4648), Base64URL (for JWTs and URLs), MIME (line-wrapped for email), or No-Padding. The tool auto-detects content: paste a Base64 image and see a live preview; paste a JWT and get a link to the JWT Decoder; paste JSON and format it. Encode any file up to 50MB by drag-and-drop. A security scanner flags passwords, API keys, and PII. All processing is browser-based — no signup, no upload to servers.

How It Works

Type or paste in the input panel, select encode or decode and your preferred variant. Output updates automatically with a short delay. Use Cmd+Enter to process immediately. In File mode, drop a file or click to pick one — the tool reads it in the browser and outputs Base64. In Image mode, paste Base64 image data to see a preview. No data is sent to any server; everything runs in your browser with no signup required.

Use Cases

Encode credentials for HTTP Basic Auth or API headers. Decode JWT tokens to inspect claims. Convert images to Base64 for data URIs in HTML or CSS. Encode file contents for email attachments (MIME Base64). Encode payloads for URL parameters (Base64URL). Check whether a string contains sensitive data with the built-in security scanner. Format JSON after decoding. All from one tool, instantly.

Frequently Asked Questions

What is Base64 encoding?
Base64 encoding converts binary or text data into a string of ASCII characters (A–Z, a–z, 0–9, +, /) so it can be safely used in JSON, URLs, or email. Each group of 3 bytes becomes 4 characters; padding with = is used when needed.
How do I decode a Base64 string?
Paste the Base64 string into the input area, select Decode mode, and the decoded text or binary (e.g. image) appears in the output. The tool auto-normalizes URL-safe characters (- and _) and padding.
What is the difference between Base64 and Base64URL?
Standard Base64 uses + and / and optional = padding. Base64URL uses - and _ and no padding, so it is safe in URLs and tokens (e.g. JWTs).
Is it safe to paste sensitive data into a Base64 decoder?
This tool runs entirely in your browser; nothing is sent to our servers. Your data never leaves your device. For extra caution, use the security scanner and avoid sharing the page URL if it contains the data in the query string.
How do I encode an image to Base64?
Switch to File mode, then drag and drop your image or click to select it. The tool will output the raw Base64 string (and show a preview). You can also paste the result into Image mode to see the preview again.
Why does Base64 encoded output end with = or ==?
Padding characters (=) make the string length a multiple of 4 so the decoder can work correctly. One = means 2 padding bytes; == means 1. Base64URL and No-Padding variants omit them.
What is MIME Base64 used for?
MIME Base64 (RFC 2045) wraps lines at 76 characters with CRLF. It is used in email attachments and multipart MIME bodies.
Can I encode large files to Base64 in the browser?
Yes. This tool supports files up to 50MB. Files over 5MB are processed in a background task so the page stays responsive.

Related Tools

JWT Decoder — decode and verify JWTs. JSON Formatter — format and validate JSON. cURL Converter — convert cURL to fetch/axios.

This base64 encoder decoder is browser-based. Your data never leaves your device.