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Base64 Decode
Decode standard Base64 or Base64URL into UTF-8 text in the browser with explicit normalization and invalid-input diagnostics.
- Base64 is reversible encoding, not encryption or authenticity validation.
- The tool processes text locally and sends neither input nor output in usage events.
Decode standard Base64 or Base64URL into UTF-8 text with explicit normalization, padding, and invalid-input diagnostics.
When to use
Use it for text values from APIs, configuration, and isolated Base64URL segments, Unicode checks, or alphabet and padding troubleshooting.
Input
Select the matching alphabet and paste up to 200,000 characters. ASCII whitespace is removed; prefixes, quotes, and comments remain invalid.
Output
Output is UTF-8 text. Errors distinguish alphabet, length, padding, and binary bytes that do not form valid UTF-8.
- Select Standard Base64 or Base64URL to match the source characters.
- Paste the input; whitespace and omitted padding are normalized only for a valid representation.
- Run decode and resolve the specific error before copying the UTF-8 text.
- Use JSON Validator for JSON, JWT Decode for complete tokens, or URL Decode for URL-encoded text.
- API payload debugging: Inspect Base64 values received in responses, webhooks, or documentation examples.
- Isolated Base64URL values: Read URL-safe fixture and integration values without treating output as JWT or authenticity validation.
- UTF-8 verification: Check whether accents, symbols, and Unicode characters survived encoding correctly.
- Base64 is not decryption: The tool does not break encryption or validate secrets; it only reverses text encoding.
- Alphabet and padding: Mixed alphabets, impossible lengths, and malformed padding are rejected instead of normalized silently.
- Binary content: The tool returns an error when bytes are not valid UTF-8; it does not create a binary preview or file.
- Sensitive data: Processing runs in the browser, but you should avoid pasting real tokens in untrusted environments.
- Base64 Decode Is Not Decryption: Practical Guide
Choose standard Base64 or Base64URL, understand padding and UTF-8 errors, and avoid treating decoded text as decrypted or authenticated data.
Decode a simple string
Input: SGVsbG8gd29ybGQ=
Output: Hello world
Restore omitted padding
Input: SGVsbG8
Output: Hello
Does Base64 Decode decrypt data?
No. Base64 only changes the byte representation and uses no cryptographic key. If the result remains encrypted, you need the correct algorithm and key outside this tool.
What happens when the input is invalid Base64?
The tool distinguishes characters outside the selected alphabet, mixed alphabets, impossible lengths, malformed padding, and bytes that are not valid UTF-8.
What is the difference between Base64 and Base64URL?
Base64URL replaces + and / with - and _ for URL-safe values. Select Base64URL for that alphabet; use JWT Decode to inspect a complete JWT.
Can I paste Base64 with spaces or missing padding?
Yes. ASCII spaces and line breaks are removed, and omitted padding is restored when the length allows one unambiguous valid Base64 representation.
Does the tool decode files or binary content?
No. Output is UTF-8 text. If the decoded bytes represent an image, compressed file, or other binary format, the tool returns a UTF-8 error instead of unreadable output.
Is my content sent or stored?
No. Decoding runs in the browser, and usage events contain neither input nor output. Avoid pasting real secrets on untrusted devices or environments.
How do I use this tool safely?
Use the tool as a short workflow: review the expected input, run processing, and validate the output: Fields: Base64 (textarea, required); Alphabet (select, required). Example workflow: SGVsbG8gd29ybGQ= -> Hello world. Enter the requested input, run the tool, and review validation messages or warnings before copying the result.