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base64

Base64 is an encoding that represents arbitrary binary data using only 64 printable ASCII characters (A–Z, a–z, 0–9, +, /). It is the standard way to embed images in HTML/CSS as data: URLs, transmit binary payloads in JSON or email (MIME), and pass file contents through APIs that only accept text. The ZTools Base64 tool encodes UTF-8 strings, raw binary files (drag-drop), and decodes Base64 back to either text or a downloadable file — all in the browser using the standard btoa/atob plus a UTF-8-safe wrapper for non-ASCII input.

Use cases​

Embedding small images in CSS as data URLs​

Drag a small icon (under ~4 KB) into the encoder, copy the Base64 output, and paste it into your CSS as background-image: url("data:image/png;base64, ..."). This eliminates one HTTP request per icon — meaningful on landing pages with many tiny assets. Above ~4 KB, the encoded size penalty (33% bloat) outweighs the request savings.

Generating Authorization: Basic headers for HTTP testing​

HTTP Basic Auth requires Authorization: Basic <base64(user:password)>. Paste myuser:mypass into the encoder, copy the result, and prepend Basic . Use this for quick API testing with curl or Postman; never use HTTP Basic Auth over plain HTTP in production (it is trivially decodable).

Decoding JWT payloads​

JWTs are three Base64URL-encoded sections separated by dots. To inspect a JWT, paste the middle section into the decoder and you get the JSON claims. (Our dedicated JWT Decoder does this in one step, but the Base64 tool works for ad-hoc inspection.)

Storing binary data in JSON or YAML​

When an API requires binary data (a PDF, a private key, an image) but only accepts JSON, Base64-encode the bytes and ship the encoded string. The receiver decodes back to the original file. Common in Kubernetes Secrets, AWS Lambda payloads, and webhook attachments.

How it works​

  1. Choose mode — Encode (text → Base64) or Decode (Base64 → text/file). The tool auto-detects when you paste, but you can lock it manually.
  2. Paste text or drop a file — Text mode handles UTF-8 (emoji, CJK, accented characters) via a TextEncoder wrapper. File mode reads the raw bytes via the FileReader API and encodes them losslessly.
  3. Click Encode (or Decode) — For text → Base64, the tool runs btoa(unescape(encodeURIComponent(input))). For Base64 → text, the inverse. For files, FileReader.readAsArrayBuffer + a custom byte-to-Base64 loop.
  4. Copy the result — Encoded output is text — one click to copy. Decoded output is either text (rendered in the right pane) or a file (Download button appears with the original MIME type detected from the bytes).
  5. Optionally use URL-safe variant — Toggle "Base64URL" to swap +/= for -_ (no padding). Required for JWTs, OAuth state parameters, and anything passed in URLs without escaping.

Examples​

Input: Hello, world!

Output: SGVsbG8sIHdvcmxkIQ==

Input: A 4KB PNG icon (binary)

Output: iVBORw0KGgoAAAANSUhEUgAA... (5.4 KB Base64)

Frequently asked questions​

Why is the encoded version longer than the original?

Base64 represents 3 input bytes (24 bits) as 4 output characters (32 bits = 4 × 8). That is a fixed 33% size increase, plus 1–2 padding = characters to align. There is no way to make it smaller without compressing the input first.

What is the difference between Base64 and Base64URL?

Standard Base64 uses +, /, and = characters. Those have special meanings in URLs (path separator, padding) so Base64URL replaces them with -, _, and drops = padding. Use Base64URL anywhere the encoded string ends up in a URL or HTTP header (JWTs, OAuth flows).

Is Base64 encryption?

No. Base64 is encoding, not encryption. The transformation is fully reversible without a key. Anything Base64-encoded is trivially decoded back to plaintext. For confidentiality, use AES (our AES Tool) or PGP.

Can I encode a 100 MB file?

In theory yes, but browsers struggle with single strings over ~256 MB. For files larger than ~50 MB, use a CLI tool (base64 < input > output.b64 on Linux/Mac, certutil -encode on Windows) or stream-encode chunks.

Why does my UTF-8 text get garbled when I decode someone else's Base64?

Some Base64 generators encode raw UTF-8 bytes, others first treat the input as Latin-1. Our tool always uses UTF-8. If the source used Latin-1, decode here, then re-encode in your target encoding to fix.

What is a data URL?

A URL of the form data:[mime];base64,[data] that embeds the file inline instead of pointing to it. Browsers render data URLs natively in <img>, CSS background-image, etc. Our encoder offers a "wrap as data URL" toggle to produce one in a single step.

Tips​

  • Use the URL-safe variant for any encoded value that ends up in a URL or query string.
  • Don't Base64-encode large images for production — <img src> with a separate request is usually faster (browser cache + parallel download).
  • Verify decoded files by checking magic bytes — a real PNG starts with 89 50 4E 47.
  • If you need JWT inspection, use our JWT Decoder instead — it splits the three parts and parses the JSON claims for you.

Try it now​

The full base64 runs in your browser at https://ztools.zaions.com/base64 — no signup, no upload, no data leaves your device.

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Last updated: 2026-05-05 · Author: Ahsan Mahmood · Edit this page on GitHub