How does Base64 encoding work?

Base64 takes 3 bytes of input (24 bits) and converts them into 4 Base64 characters (6 bits each). If the input length is not divisible by 3, padding characters (=) are added to make the output length a multiple of 4. The encoded output is always exactly 4/3 times the original size (plus padding).

What is Base64 used for?

Common uses include: embedding images in HTML/CSS as data URIs, encoding binary attachments in email (MIME), transmitting binary data in JSON APIs, encoding authentication credentials in HTTP Basic Auth headers, storing binary data in XML or text-based config files, and URL-safe data transmission (Base64url variant).

What is the difference between encode and decode?

Encoding converts plain text or binary data into a Base64 string (the output is longer and looks like random characters). Decoding reverses the process, converting a Base64 string back to the original text or binary data. If you have a Base64 string and want to read its content, use decode mode.

Does Base64 provide encryption or security?

No. Base64 is an encoding scheme, not encryption. It is easily reversible by anyone — just paste the Base64 string into any decoder. It should never be used to hide sensitive data. For security, use proper encryption algorithms (AES, RSA) or cryptographic hashing (SHA-256) instead of Base64.

What is URL-safe Base64?

Standard Base64 uses + and / characters that have special meaning in URLs. URL-safe Base64 (Base64url) replaces + with - and / with _, making the encoded string safe to include in URL query parameters without percent-encoding. JWT tokens, for example, use Base64url encoding.

Why does Base64 encoding increase file size?

Base64 uses 4 characters to represent every 3 bytes of data, so the encoded size is always 4/3 × original = ~33% larger. Additionally, the = padding characters add a few extra bytes. This size increase is the trade-off for safe text transmission. For large files, compression before encoding can partially offset this increase.

Base64 Encoder

Encode and decode Base64 strings instantly in your browser.

Encode & decodeUnicode supportClient-side only

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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 widely used to embed images as data URIs in HTML and CSS, encode JWT tokens, transmit binary data in JSON APIs, encode PEM certificates, and handle MIME email attachments. In JavaScript, use btoa() to encode and atob() to decode — for Unicode text you need the encodeURIComponent wrapper, which this tool handles automatically. Note: Base64 is encoding, not encryption — anyone can decode it without a key.

Frequently asked questions

Base64 is a binary-to-text encoding that converts binary data to a string of 64 ASCII characters (A-Z, a-z, 0-9, +, /). It encodes every 3 bytes of binary data into 4 characters, resulting in a ~33% size increase. The "=" character is used as padding at the end.

Base64 is used to: embed images in HTML/CSS as data URIs, encode binary attachments in emails (MIME), transmit binary data in JSON APIs, encode SSL/TLS certificates in PEM format, and store binary data in text-based databases or config files.

Base64 works by taking 3 bytes (24 bits) of input data at a time, splitting them into four 6-bit groups, and mapping each group to one of 64 printable characters using a lookup table. If the input is not a multiple of 3 bytes, padding characters (=) are added.

No. Base64 is encoding, not encryption. It transforms data into a different representation but does not protect it. Anyone can decode Base64 without a key. For security, use proper encryption (AES, RSA). Base64 is often confused with encryption because the output looks random, but it is trivially reversible.

Padding characters (=) are added to make the encoded string a multiple of 4 characters. If the input is a multiple of 3 bytes, no padding is needed. 1 extra byte → two padding characters (==). 2 extra bytes → one padding character (=).

Standard Base64 uses + and / which are special characters in URLs. Base64URL replaces + with - and / with _ for safe use in URLs and filenames. JWT tokens use Base64URL encoding. This tool uses standard Base64.

This tool uses encodeURIComponent/decodeURIComponent around atob/btoa to handle Unicode text correctly. Standard btoa() in JavaScript only handles ASCII and will throw an error with non-ASCII characters. The tool handles all Unicode text including emoji, CJK, Arabic, Cyrillic and other scripts.

What is Base64 encoding?

Frequently asked questions

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