Online Base64 Decoder

Base64 Decoder

Base64 is a safe transport encoding that turns binary data into readable ASCII characters so it can be sent in URLs, headers, or text-based files. A Base64 decoder reverses that process and reveals the original text or data. This tool is built for quick inspection of encoded payloads in APIs, configuration files, environment variables, logs, and tokens. It runs entirely in your browser, which means your data stays on your device and is never uploaded.

What Base64 decoding is used for

Many systems encode values in Base64 to avoid control characters or binary data issues. Developers decode Base64 when troubleshooting integrations, validating authentication headers, or reading compressed or embedded strings. When you encounter a field that looks like eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9, it is likely Base64 or Base64URL. Decoding lets you see the original content and make meaningful decisions about formatting, structure, or security.

Common real-world scenarios

• HTTP Basic Auth: The Authorization: Basic header contains a Base64 encoded username:password string. Decoding helps you verify test credentials.
• API payloads: Some APIs embed JSON or files in Base64 within a larger JSON body. Decoding reveals the actual data.
• JWT inspection: JSON Web Tokens use Base64URL for the header and payload sections. Decoding helps you understand claims without verifying a signature.
• Data URLs: Images or files in a data URL use Base64. Decoding helps you confirm the content or recover raw bytes.
• Config values: Environment variables or CI pipelines often store secrets or configs in Base64. Decoding validates what was stored.

How to decode Base64 strings

1. Paste the Base64 string into the left editor. The tool accepts multi-line values.
2. Click Decode to convert it back into text.
3. Copy the decoded output or download it for analysis.

If the encoded string contains - and _ characters, it is likely Base64URL. This tool handles both formats by normalizing URL-safe input before decoding.

Example: decode an HTTP header

Suppose you see a header like this in logs:

Authorization: Basic YWxleDpwYXNzMTIz

Decoding YWxleDpwYXNzMTIz reveals:

alex:pass123

This helps you quickly confirm which test account is being used without guessing or manually decoding.

Common errors and fixes

• Invalid length: Base64 strings are padded with = characters. If decoding fails, add missing padding or check for truncated input.
• Unexpected characters: Base64 allows only letters, digits, +, /, and =. Base64URL uses - and _. Remove spaces or line breaks that do not belong.
• Garbled output: If the decoded text looks like random symbols, the original data might be binary (such as a file). Try saving the output as a file instead of reading it as text.
• Unicode issues: If accents or non-Latin characters look broken, ensure the output is treated as UTF-8. The tool decodes as UTF-8 by default.
• JWT confusion: JWT uses Base64URL without padding. If you paste a token segment, the decoder will still work, but you must decode each segment separately.

Best practices

• Always verify the decoded output matches the expected structure (JSON, XML, or plain text).
• Store only what you need; avoid Base64 for large files if a binary upload is available.
• Use JSON Validator if the decoded output is JSON to catch syntax errors early.
• Be cautious with secrets. Decode locally and do not paste sensitive data into untrusted websites.

Decoding data URLs

Data URLs embed content directly in HTML or CSS, such as data:image/png;base64,iVBORw0KGgo.... To decode them, remove the metadata prefix and keep only the Base64 content. This lets you inspect the raw bytes or recover an image file. If the output looks unreadable, save it as a binary file and open it with the appropriate viewer.

Security checklist

Because Base64 is not secure, always treat decoded content as sensitive data. Avoid sharing decoded secrets, credentials, or token payloads. When decoding JWTs, remember that the signature still needs verification. For production issues, consider rotating tokens or revoking compromised credentials instead of sharing the raw decoded output.

Troubleshooting encoded payloads

If a decoded string still looks incorrect, check for double encoding. Some systems Base64-encode a JSON string that is itself Base64-encoded, resulting in nested encodings. Decode once, then check if the output still looks like Base64. Also verify whether the original data was compressed before encoding. In those cases you need to decode and then decompress using gzip or a similar tool.

Automation tips

When you find yourself decoding many values, automate the workflow in your scripts or tests. Most languages have Base64 libraries. Use this online decoder for quick debugging, then embed the same logic in your application or CI pipeline so you can reproduce results consistently.

Quality checks

After decoding, check whether the output is valid JSON, XML, or plain text. If you expect JSON, run it through JSON Validator and look for missing quotes or invalid commas. If you expect XML, verify the root tag and closing tags. These quick checks prevent you from chasing errors that are actually caused by malformed input rather than the system you are testing.

Clipboard and formatting tips

When copying Base64 from logs or terminals, watch for invisible characters like line breaks or spaces. These extra characters can break decoding. Paste the string into a plain-text editor or remove whitespace before decoding. If the output includes trailing null characters or strange symbols, the original data may be binary, so save it as a file instead of reading it as text.

FAQs

Is Base64 encryption? No. Base64 is not encryption; it is only encoding. Anyone can decode it.

Why does Base64 add extra characters? It expands data by about 33%. This tradeoff allows safe transmission in text-only channels.

Can I decode files? Yes, if the file was encoded as Base64. You can paste the string and download the decoded result.

What is Base64URL? It is a URL-safe variant that replaces + with - and / with _, often used in JWTs.

Does this tool store my data? No. Everything runs in your browser; nothing is uploaded or saved.

How do I decode a data URL? Remove the prefix (for example, data:image/png;base64,) and paste only the Base64 content.