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FeuTex · free tools runs in-browser no bloat built by LiMiT

Base64 Encoding Checker

Validate whether a string is properly Base64-encoded, normalize it (padding, URL-safe alphabet, whitespace), and decode it to UTF‑8 when possible. You can also encode plain text to Base64.

Category: Developer · URL: /tools/base64-encoding-checker.html
Privacy: runs locally in your browser. No uploads, no tracking scripts.

How to use

Use it in one of two modes:

  1. Check & Decode: paste a Base64/Base64URL string, optionally allow whitespace, then run to see validity, normalization, and decoded output.
  2. Encode Text: paste text, choose URL-safe or strip padding if needed, then run to get Base64.
Keywords this page targets (natural cluster): base64 encoding checker, check base64 encoding online, validate base64 string, is this base64, base64 padding checker, base64 normalize padding, base64 decode validator, base64 url safe checker, base64url vs base64 check, remove base64 whitespace, base64 decode to text, base64 decode utf-8, base64 invalid character check, base64 length multiple of 4, base64 encoder online, text to base64, base64 to bytes hex, base64 strict validation
Secondary intents covered: Validate if an input is Base64 without decoding errors, Normalize Base64 by fixing or adding missing padding, Handle Base64 strings containing whitespace/newlines, Accept and convert Base64URL (- and _) into standard Base64, Decode Base64 to readable UTF‑8 text (or show bytes when not text), Encode plain text to Base64 (standard or URL-safe), Quickly copy the normalized/decoded output, Troubleshoot why a Base64 string fails in code

FAQ

What does this Base64 encoding checker validate?

It checks character set, padding placement, and length rules, then attempts a real decode to confirm the Base64 is usable.

Can it handle Base64 with spaces or newlines?

Yes—enable “Allow whitespace” to ignore whitespace characters before validation and decoding.

What is Base64URL and how is it different?

Base64URL uses - and _ instead of + and /, often with optional padding removed.

Why does it say “not valid UTF-8” after decoding?

The bytes are valid, but they don’t form valid UTF‑8 text (for example, compressed/binary data). Use the hex/byte info instead.

Is missing padding always an error?

Not always—many systems omit =. This tool can add the required padding to normalize and decode.

Does this tool upload my data?

No. Everything runs locally in your browser; there are no network calls in the tool logic.

How do I quickly run it from the keyboard?

Press Ctrl+Enter (Windows/Linux) or Cmd+Enter (macOS) to run.