Fix the base64 problems you actually hit
Base64 breaks easily when copied from email, chat, logs, or JSON. base64app repairs before decoding and shows what changed.
- Whitespace and line breaks
- data:...;base64, prefixes
- URL-safe alphabet (- and _)
- Missing or wrong = padding
- Stray quotes and invalid characters
How it works
- 1. Paste the broken base64 string into the decoder above.
- 2. Keep auto-repair enabled (recommended).
- 3. Click Decode — review the repair log, preview, and download.
Common errors
- Invalid characters — standard base64 only uses A–Z, a–z, 0–9, +, /, and = padding.
- Missing or wrong padding — length should be a multiple of 4; add = at the end if needed.
- Line breaks and spaces — email, Slack, and JSON often insert whitespace that must be stripped.
- data: URI prefix left on the string — remove data:<mime>;base64, before decoding.
- URL-safe alphabet — JWTs and some APIs use - and _ instead of + and /.
- Truncated payload — a copied string cut off mid-way cannot be fully recovered.
Frequently asked questions
What kinds of corruption can be fixed?
Whitespace, data URI prefixes, URL-safe chars, bad padding, and stray invalid characters. Severely truncated data may only partially decode.
Can I validate without repairing?
Yes. Turn off auto-repair to require strictly valid base64.
Will repairs change my file?
Repairs fix encoding only — underlying bytes stay the same once decoded correctly.
How do I know what was fixed?
The repair log lists every change applied to the string.
Is my data uploaded when I decode?
No. All processing runs in your browser. Nothing is uploaded, stored, or logged.
Can base64app fix corrupted base64?
Yes. Auto-repair fixes whitespace, data URI prefixes, URL-safe characters, padding, and stray characters.
Is base64app free?
Yes — free with no sign-up required.