Base64 Encoder/Decoder

Invalid padding

Symptom: Invalid padding: expected 0-2 '=' characters or decoding fails silently.

Cause: Base64 strings must have a length that is a multiple of 4. Missing = padding characters break the decoder.

Fix: Add = characters until the string length is a multiple of 4. This tool does it automatically — look for the "Auto-repaired: added padding" message.

Invalid character in Base64 string

Symptom: Invalid character error when decoding.

Cause: The string contains characters outside the Base64 alphabet. Common culprits: - and _ (Base64URL characters) in a standard Base64 decoder.

Fix: Check if the string is Base64URL-encoded (uses -_ instead of +/). Select the correct format or let auto-detect identify it.

Decoded output is garbled or unreadable

Symptom: The decoded result contains random characters or mojibake.

Cause: The wrong encoding format was selected. For example, a Base32 string decoded as Base64 produces garbage output.

Fix: Use auto-detect to identify the correct format, or manually try different formats until the output makes sense.

Base64URL vs Base64 confusion

Symptom: JWT tokens fail to decode with a standard Base64 decoder.

Cause: JWT uses Base64URL encoding which replaces + with - and / with _, and omits padding.

Fix: Select Base64URL format, or paste the JWT and let auto-detect handle it (strings starting with eyJ are automatically detected as JWT/Base64URL).

Odd-length hex string

Symptom: Odd-length hex string error when decoding hex.

Cause: Hex encoding uses 2 characters per byte, so the total length must be even. An odd-length string is missing a leading zero.

Fix: Prepend a 0 to make the length even. For example, change FFF to 0FFF.

Is Base64 encoding the same as encryption?

No. Base64 is encoding, not encryption. Anyone can decode Base64 without a key — it simply converts binary data to a text-safe format. For security, use actual encryption algorithms like AES or RSA. Never store sensitive data in Base64 alone.

Why does Base64 increase file size by 33%?

Base64 maps every 3 bytes of input to 4 ASCII characters using 6-bit groups. Since 4/3 ≈ 1.333, the output is always ~33% larger than the input. This trade-off provides safe text transmission through protocols that only support ASCII characters.

When should I use Base64URL instead of standard Base64?

Use Base64URL when the encoded string will appear in URLs or filenames. Standard Base64 uses + and / which have special meaning in URLs. Base64URL replaces them with - and _ and omits padding. JWT tokens always use Base64URL.

What is the difference between Base32 and Base64?

Base32 uses only uppercase letters (A-Z) and digits 2-7, making it case-insensitive with ~60% size overhead. Base64 uses 64 characters (case-sensitive) with ~33% overhead. Base32 is preferred for TOTP secrets and systems where case sensitivity is problematic.

Can I encode binary files like images with Base64?

Yes. Base64 is commonly used to embed images in HTML/CSS as Data URIs (data:image/png;base64,...), encode email attachments (MIME), and transmit binary data through JSON APIs. This tool supports file drag-and-drop for encoding any file type.

Why does Base58 exclude certain characters?

Base58 removes 0 (zero), O (uppercase o), I (uppercase i), and l (lowercase L) from the alphabet to prevent visual confusion when reading addresses. This makes it ideal for Bitcoin addresses and other human-readable identifiers.

What is the maximum size I can encode with this tool?

This tool supports files up to 10MB. All processing happens client-side in your browser, so performance depends on your device. For text input, there is no strict limit, but very large inputs (over 1MB) may cause slower processing.

Is it safe to paste sensitive data like tokens here?

Yes. All processing happens entirely in your browser using JavaScript. Your data is never sent to any server. You can verify this by checking the Network tab in your browser's developer tools.