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Base64 Checker

Validate Base64 strings quickly, decode them to readable text, or encode plain text into Base64. Options include whitespace handling and Base64URL support.

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

How to use

Paste your input, choose options, then run a check or conversion.

  1. Paste Base64 (or text to encode) into the input box.
  2. Optional: enable whitespace ignoring and Base64URL auto-detect.
  3. Click Check to validate, Decode to decode, or Encode to encode.
  4. Copy the output if needed.
Keywords this page targets (natural cluster): base64 checker, base64 validator, check base64 string, is this base64 valid, base64 decode online, base64 encode online, base64url checker, base64url decode, base64 padding checker, base64 without padding, base64 whitespace newlines, validate base64 regex, base64 invalid character, decode base64 to text, encode text to base64, base64 to utf-8, base64 error finder, base64 normalize input
Secondary intents covered: Validate whether a string is correctly formatted Base64, Decode Base64 into readable UTF-8 text, Encode plain text into Base64, Detect common issues (bad characters, wrong padding, wrong length), Handle Base64 with spaces/newlines from logs or PEM blocks, Work with Base64URL (- and _) and optional padding

FAQ

What does a Base64 checker do?

It validates whether a string is properly formatted Base64 and (optionally) attempts to decode it to confirm it’s actually decodable.

Why does my Base64 fail validation even though it looks close?

Common causes are invalid characters, incorrect padding (=), or a length that’s impossible for Base64 (for example length mod 4 equals 1).

Is missing padding (=) always invalid?

No. Many systems omit padding; disable “Require padding (=)” to accept valid unpadded Base64.

What is Base64URL and how is it different?

Base64URL replaces + and / with - and _, and often removes padding. Enable auto-detect or Base64URL decoding for these strings.

Can I decode binary data with this tool?

This tool decodes to UTF-8 text output. If the decoded bytes aren’t text, the result may look garbled.

Does whitespace/newlines break Base64?

Whitespace is common in copied logs or wrapped strings; enable “Ignore whitespace/newlines” to validate and decode correctly.

Is my input sent to a server?

No. The tool runs locally in your browser and doesn’t make network requests.