Free Base64 Encoder & Decoder

What Base64 is (and isn’t)

Base64 is an encoding scheme that represents binary data using only 64 printable ASCII characters: A–Z, a–z, 0–9, plus + and /, with = as padding. It’s used everywhere text-only channels need to carry binary data — email attachments (MIME), embedded images in HTML/CSS (data: URIs), JSON Web Tokens (JWTs), API request bodies that carry files, PGP messages, and configuration files that need to embed certificates or keys. This free Base64 encoder handles both text and file input, supports URL-safe encoding for use in URLs and JWTs, and does everything client-side — nothing you paste or upload leaves your browser.

Base64 is not encryption. Anyone can decode a Base64 string in less than a second — the process is fully public and reversible without any key. Never use Base64 to protect passwords, API keys, or sensitive data. It only makes binary data safe to transmit through text-only channels; it does not obscure it.

How to use the Base64 encoder

1. Pick your mode — Encode (text or file → Base64) or Decode (Base64 → text or image).
2. Paste your input into the text box, or click 📎 Encode a file to select any file (image, PDF, ZIP — anything).
3. Choose options: URL-safe swaps + and / for - and _ (needed for JWTs and URL query parameters). Remove padding strips trailing = characters.
4. Click Convert →. The result appears below with size info. If you decoded an image data URI, we render a preview automatically.
5. Copy or download using the buttons at the top right.

Common use cases

Data URI images in HTML and CSS

Embed a small icon directly in a stylesheet or HTML file without a separate image request:

<img src="data:image/png;base64,iVBORw0KGgo…">

This trick is great for tiny icons (under 2 KB) and eliminates an HTTP request. Larger images cost more in Base64 overhead (~33% size increase) than they save in request time, so keep it small.

JWT token inspection

JSON Web Tokens have three Base64URL-encoded parts separated by dots: header.payload.signature. Paste each part (or use our dedicated JWT Decoder) to see what’s inside a token from your app’s auth system. The signature can only be verified with the secret; the header and payload are always readable.

Sending files through JSON APIs

REST APIs that only accept JSON can’t carry binary directly. Encode the file to Base64, embed it as a string field, and decode on the server. Common in image-upload APIs, chatbot file inputs, and integration webhooks.

Embedding certificates and keys in config

Cloud config formats like Kubernetes manifests and Terraform sometimes embed X.509 certificates or SSH keys as Base64-encoded strings to keep line breaks and special characters from breaking YAML/JSON parsing.

Email attachments (MIME)

Every attachment you’ve ever sent by email was silently Base64-encoded by your email client, then decoded on the recipient’s side. You never see the encoding, but it’s what makes email attachments work over the ancient text-only SMTP protocol.

URL-safe Base64 explained

Standard Base64 uses + and /, which have special meaning in URLs (+ encodes as space in query strings; / separates path segments). URL-safe Base64 (defined in RFC 4648 §5) swaps them for - and _, which have no special URL meaning. It’s the standard encoding for:

• JSON Web Tokens (JWTs)
• OAuth 2.0 tokens and codes
• URL-embedded data payloads
• Filenames that carry encoded IDs

Enable the “URL-safe” toggle in this tool whenever the output will end up in a URL or JWT. Combine with “Remove padding” to strip trailing = characters — most URL-safe use cases don’t preserve them.

The math of Base64 overhead

Base64 encoding takes 3 bytes of binary and turns them into 4 ASCII characters. That’s a fixed 33% size increase (before padding). A 3 MB image becomes about 4 MB of Base64 text. That overhead is why:

• Data URI images should be tiny (under 2 KB is ideal)
• Uploading large files via Base64 through JSON APIs is slower than uploading them as binary through multipart/form-data
• Databases storing binary as Base64 use 33% more space than storing it as BLOB

For truly large files, use binary transfers and file APIs rather than Base64 embedding.

Base64 encoder comparison

Pro tips

• Data URI images should stay under 2 KB. Beyond that, a normal image file with an HTTP request is faster because Base64’s 33% overhead outweighs the saved request.
• JWTs have no padding. Decode a JWT part manually by padding it with = until length is a multiple of 4, then use our Decode mode. Our tool handles this automatically if you paste in a JWT part.
• Base64URL for cookies. If you’re encoding data into a cookie, URL-safe Base64 avoids the encoding issues that + and / can cause in some browsers and load balancers.
• Never Base64 a password. Base64 is not encryption. If you’re storing or sending passwords, use proper hashing (bcrypt, Argon2) or an encrypted vault.
• Big files freeze the UI briefly. Very large file encoding (100 MB+) runs synchronously in the browser and may lock the tab for a moment. This is a browser limitation; the alternative is streaming, which requires a server.