Base64 Decode
Decode Base64 to plain text in your browser. Auto-detects the URL-safe variant, tolerates missing padding and whitespace/line breaks. Uses native atob with UTF-8 decoding via TextDecoder.
Base64 in, text out
Each 4 Base64 characters become 3 bytes of output. Padding and whitespace are tolerated unless strict mode is on.
SGVsbG8sIHdvcmxkIQ==
Hello, world!
What you'll use this for
Base64 is the lingua franca of "binary over text" channels — embed bytes inside JSON, HTTP, URLs, email, or environment variables.
HTTP Basic auth
Decode the value of an Authorization: Basic ... header to inspect the user:password.
JWT payload
Decode a JWT's middle segment (URL-safe Base64) to see the claims.
Data URIs
Pull out the bytes of a data: URI to inspect file content.
Email headers
Decode MIME-encoded headers that wrap non-ASCII in Base64.
How to Base64-decode text
Paste your Base64
Standard or URL-safe; padding optional with auto-detect.
Pick variant
Auto handles both; force one if you know the format.
Click Decode
Runs locally with atob + UTF-8 decode.
Copy or download
Copy to clipboard or save as .txt.
Frequently asked questions
Yes. The decoder converts Base64 to bytes, then decodes those bytes as UTF-8 — so non-ASCII text round-trips correctly.
By default whitespace is stripped before decoding (MIME-style input works). Toggle Strict mode to reject any non-Base64 character.
Yes. No signup, no limits, no ads.
Auto-detect adds the missing = characters. Strict mode requires exact padding.
Standard Base64 uses + and /; URL-safe uses - and _ so the output is safe in URLs. Auto-detect spots URL-safe input by the presence of - / _.
About Base64 decoding
RFC 4648 defines two Base64 alphabets: the standard alphabet (+, /) and the URL-safe alphabet (-, _). Both round-trip through this decoder.
How decoding works
- Strip whitespace (unless strict mode is on).
- Convert URL-safe characters back to standard (if URL-safe detected).
- Pad with
=to a length multiple of 4. - Run native
atobto get a byte string. - Decode bytes as UTF-8 with
TextDecoder.
What it can't decode
- Binary data shown as text. If the original bytes don't form valid UTF-8 (e.g. a PNG file), the output will contain replacement characters.
- Non-Base64 input. Strict mode rejects unknown characters; loose mode silently strips them.