Why is Base64 output larger than the input?

Base64 encodes every 3 bytes as 4 characters, so output is roughly 33% larger than input. Files of size N produce ceil(N/3)*4 Base64 characters plus optional padding (=). The size cost is the trade-off for being able to embed binary data anywhere text is allowed.

What is URL-safe Base64?

URL-safe Base64 (RFC 4648 §5) replaces + with - and / with _ so the output can appear in URLs and filenames without percent-encoding. JWTs and many web APIs use this variant. Standard Base64 uses + and / and may need URL encoding when appearing in query strings.

What does the = padding mean?

The trailing = characters pad Base64 output to a multiple of 4 characters. Inputs whose length is divisible by 3 have no padding; one leftover byte produces ==, two leftover bytes produce =. Padding is required by strict parsers but often omitted in URL-safe variants.

Is Base64 encryption?

No — Base64 is encoding, not encryption. Anyone can decode Base64 back to the original bytes with a single function call. Never use Base64 to "hide" secrets. For real protection, use AES, RSA, or a proper authenticated encryption library.

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Base64 Encoder / Decoder

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Encode and decode Base64 strings instantly. Supports text and file input.

—Text

—Encoded

—Overhead

Input

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Output

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✨ AI Code Explanation

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What Is Base64 Encoding?

Base64 is a binary-to-text encoding scheme that represents binary data using only 64 printable ASCII characters (A–Z, a–z, 0–9, +, /). It allows any data — text, images, binary files — to be safely transmitted over systems that only handle text, such as HTTP headers, JSON payloads, email bodies, and URLs.

How to Encode or Decode Base64 Online

Select Encode to convert text → Base64, or Decode to convert Base64 → text.
Paste your input into the left pane, or click Load Sample.
Choose Std (standard) or URL (URL-safe) variant.
For encoding: enable 76-char wrap if you need MIME/PEM line-wrapped output.
For decoding: enable Auto-fix to strip whitespace and fix missing padding automatically.
Click Encode or Decode — or turn on Live mode to convert as you type.
Use ⇄ Swap to instantly flip the input/output and reverse the mode.
To encode a file, drag it into the File → Base64 panel below the editor, or click to browse.

Standard vs URL-safe Base64

Standard (Std) — uses + and / with = padding. Used in email (MIME), PEM certificates, HTTP Basic Auth, and most general-purpose Base64.
URL-safe (URL) — replaces + with - and / with _, drops padding. Required for JWTs, OAuth tokens, and Base64 embedded directly in URLs.

Common Use Cases

JWT tokens — the header and payload segments are URL-safe Base64. Switch to URL variant to decode them (or use the JWT Decoder for full token inspection).
Data URIs — embed images directly in HTML/CSS: url('data:image/png;base64,...'). Use the File panel to generate data URIs from any image.
HTTP Basic Auth — encodes username:password in standard Base64 for the Authorization header.
Email attachments (MIME) — MIME requires Base64 with 76-character line wraps. Enable 76-char wrap for this format.
Binary data in JSON APIs — encode binary payloads as Base64 strings to embed them in JSON safely.

Common Base64 Decoding Errors

Invalid character — the input contains a character outside the Base64 alphabet. Enable Auto-fix which strips whitespace and newlines before decoding.
Incorrect padding — Base64 strings must be a multiple of 4 characters. Auto-fix adds missing = padding automatically.
Garbled output — if decoded text looks like gibberish, the input may be URL-safe Base64 (- and _ instead of + and /). Switch to URL variant.
Binary output — decoding a file's Base64 produces binary data that won't display correctly as text. Use the browser's native tools or download the output instead.

How Much Does Base64 Increase File Size?

Base64 encoding increases data size by approximately 33% — every 3 bytes of input become 4 Base64 characters. With 76-character line wraps (MIME), the overhead is slightly higher due to the added newlines. The stats badge on this tool tracks the exact input vs output byte count for every conversion.

Related Tools

JWT Decoder — inspect Base64-encoded JWT header and payload
URL Encoder / Decoder — percent-encode special characters for URLs
Hash Generator — generate MD5, SHA-256, and other hashes

Is My Data Sent to a Server?

No — all encoding, decoding, and file processing run entirely in your browser using native Web APIs (btoa, atob, FileReader). Your text and files never leave your machine.