What is Base64 Encoding?
Base64 is a binary-to-text encoding scheme. It represents arbitrary byte sequences using 64 printable ASCII characters, making it safe to embed in JSON, XML, URLs, and email bodies that only accept text.
The name comes from the 64-character alphabet: uppercase letters, lowercase letters, digits, plus + and /, with = used for padding when input length is not a multiple of three bytes.
When to Use Base64
Data URIs — Embed small images or fonts directly in HTML or CSS: data:image/png;base64,iVBORw0KG....
HTTP Basic Authentication — The Authorization header encodes username:password as Base64 (over HTTPS only).
API payloads — Some endpoints accept Base64-encoded files or certificates in JSON fields when multipart upload is unavailable.
Debugging — Developers encode strings to compare with server output or test decoding pipelines.
How UTF-8 Affects Encoding
This tool encodes text as UTF-8 before applying Base64. The ASCII string hello and the Unicode string café produce different byte sequences — and therefore different Base64 output. Always confirm your receiving system expects UTF-8-encoded Base64, which is the modern default.
Base64 vs Encryption
Encoding transforms data format; encryption transforms data secrecy. Base64 output is human-readable gibberish but trivially reversible with any decoder. Never rely on Base64 alone to protect passwords, API keys, or personal information. Use proper encryption (AES, TLS) when confidentiality matters.
To reverse an encoded string, use the Base64 Decode tool.
Worked Examples
| Plain text input | UTF-8 bytes | Base64 output | Output length |
|---|---:|---|---:|
| Hi | 2 bytes (48 69) | SGk= | 4 chars (1 = pad) |
| Hello | 5 bytes | SGVsbG8= | 8 chars (1 = pad) |
| Hello World | 11 bytes | SGVsbG8gV29ybGQ= | 16 chars (1 = pad) |
| user:pass123 | 12 bytes | dXNlcjpwYXNzMTIz | 16 chars (0 pad — multiple of 3 bytes) |
| {"ok":true} | 11 bytes | eyJvayI6dHJ1ZX0= | 16 chars |
The output length grows because every 3 bytes (24 bits) of input split into four 6-bit Base64 characters. Padding = characters appear at the end whenever the input byte count is not divisible by 3. To reverse an encoded string, paste it into Base64 Decode, or format JSON payloads first with the JSON Formatter.
Encoding Pitfalls to Avoid
- Encoding already-encoded data — Double-encoding produces a longer string that decodes to Base64 text, not the original message.
- Mixing character encodings — Encoding Latin-1 text as UTF-8 bytes produces different Base64 than expected. Confirm encoding with your API documentation.
- Pasting line breaks — Email and chat apps sometimes wrap long Base64 strings. Remove whitespace before decoding.