What is Base64 Validation?
Base64 validation checks whether a string conforms to the Base64 encoding specification defined in RFC 4648. A valid Base64 string contains only 64 permitted characters (A-Z, a-z, 0-9, +, /) plus = padding. This validator verifies the character set, padding correctness, and data integrity.
Why Validate Base64 Strings?
Invalid Base64 strings cause decoding failures, application crashes, and corrupted data output. Validation catches 4 categories of errors before they reach production systems.
- Truncated data: Incomplete API responses or copy-paste errors produce strings that fail decoding.
- Character corruption: Non-Base64 characters inserted during transmission break the encoding.
- Padding errors: Missing or misplaced
=characters produce incorrect byte alignment. - Format mismatches: A string may be valid Base64 but not represent the expected data type (image, PDF, text).
After validation, use the Base64 image decoder or file decoder to extract the original data.
How Does the Base64 Validator Work?
The validator runs 5 checks in sequence: character set verification, padding correctness, length divisibility by 4, successful atob() decoding, and file signature detection. If the string includes a data URI prefix, the validator extracts the MIME type automatically.
What Image Formats Does the Validator Detect?
The validator identifies image formats by reading the first 4 bytes of decoded data (the file signature or "magic number"). The table below lists the supported signatures.
| Format | File Signature (Hex) | Magic Bytes |
|---|---|---|
| PNG | 89 50 4E 47 | \x89PNG |
| JPEG | FF D8 FF | \xFF\xD8\xFF |
| GIF | 47 49 46 | GIF |
| WebP | 52 49 46 46 | RIFF |
| BMP | 42 4D | BM |
| SVG | 3C 73 76 67 | <svg |
For hex-level inspection of encoded data, use the Base64 to HEX converter.
What Are Common Base64 Validation Errors?
The validator identifies 5 specific error types and provides feedback for each one. Invalid characters outside the 64-character alphabet cause immediate rejection. Padding errors occur when = appears in positions other than the final 2 characters. Length errors indicate the string is not a multiple of 4 characters. Whitespace or line breaks within the string cause parsing failures. Decoding failures suggest the data is corrupted even if the character set is valid.
What is the Structure of a Valid Base64 String?
A valid Base64 string follows 4 structural rules defined in RFC 4648. The string uses only the 64-character alphabet plus optional = padding. The padded length is a multiple of 4. Padding (= or ==) appears only at the end. Data URIs prepend a MIME type prefix: data:image/png;base64,.
To encode text to Base64 or convert to URL-safe Base64, use the respective tools and then validate the output here.
Is This Validator Private and Secure?
All validation runs locally in your browser using JavaScript. Zero data is transmitted to external servers. Your Base64 strings, decoded data, and image previews remain entirely on your device.
Frequently Asked Questions
How do I validate a Base64 string?
Paste your Base64 string into the text area above. The validator instantly checks character validity, padding, length, and decodability. Results display within milliseconds.
What makes a Base64 string invalid?
A Base64 string is invalid if it contains characters outside A-Z, a-z, 0-9, +, /, and =. It is also invalid if the padded length is not a multiple of 4 or if = characters appear in incorrect positions.
Can this validator detect the image format?
Yes. The validator detects image formats in 2 ways: by parsing the data URI MIME type prefix (e.g., data:image/png;base64,) and by reading the decoded binary file signature (magic bytes).
Why does my valid-looking Base64 fail validation?
Common causes include invisible whitespace characters, line breaks inserted by email systems (MIME wraps at 76 characters), incomplete copy-paste truncation, or incorrect padding. The validator identifies the specific error type.
Is this validator safe for sensitive data?
Yes. All validation runs in your browser. Zero data leaves your device. No network requests are made during validation.