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Encoding
Base64
Boundary
Text or bytes
Runtime
Browser

Strictly decode Base64 with no MIME cleanup

Recover bytes from one chosen Base64 profile without whitespace stripping or alphabet guessing.

Local processingNo sign-upNo files or upload

Decode Base64

Limited to 512 KiB of bytes and 1 MiB of encoded text.

Tool Swim does not upload, fetch, save, log, convert files, or create presets from these values.

Decoded byte report

Decoder reports keep lowercase hexadecimal authoritative.

What this tool proves

Explicit byte-to-text semantics

This decoder is intentionally not a MIME parser. Spaces, line wrapping, misplaced padding, mixed +/_ characters, and illegal tail lengths fail.

Strict Base64 is narrower than permissive transport decoders

This decoder is intentionally not a MIME parser. Spaces, line wrapping, misplaced padding, mixed +/_ characters, and illegal tail lengths fail.

Successful bytes must reproduce the exact selected padded or unpadded representation when re-encoded.

Bytes stay explicit, private, and bounded

Encoder text is converted with UTF-8 only after malformed surrogate pairs are rejected. Hex mode accepts exact byte pairs without 0x, spaces, or separators. Decoder hex is authoritative; a text preview appears only when the bytes are valid UTF-8.

The work starts only when you submit the form. Source text, byte values, and results stay in the current browser tab; Tool Swim does not upload them, log their content, save presets, or call a developer API.

Base16, Base32, Base64, and Base85 allow at most 512 KiB of source or decoded bytes and 1 MiB of encoded text. Bitcoin Base58 is limited to 4,096 bytes or 5,600 characters because generic radix conversion is quadratic.

Primary references

Questions and answers

Related Base Encoding tools

Base64 EncoderSelect standard Base64 or Base64url and retain or omit its canonical padding deliberately.Base32 DecoderDecode one chosen Base32 profile without case folding, ambiguous glyph mapping, or padding repair.Base16 DecoderValidate hexadecimal byte pairs and inspect their exact bytes plus an optional valid UTF-8 view.