What is base64 decoding?
Base64 encoding turns binary data into ASCII text so it can travel through JSON, email, URLs, and databases. Decoding reverses that process: the base64 string is translated back into the original bytes, which might be a PDF, a PNG, a ZIP archive, or a UTF-8 text file.
base64app decodes locally in your browser, detects the real file type from magic bytes, previews when possible, and lets you download with the correct extension. No upload is required.
When developers use base64 decode
API responses often embed files as base64. Email and chat paste long encoded strings. Frontend apps receive data: URIs from CSS or HTML. Logs and databases store binary blobs as text. base64app handles all of these — including messy copies with line breaks or missing padding.
- REST API payloads with embedded files
- data:application/pdf;base64 and data:image/png URIs
- JWT segments (URL-safe base64)
- Email attachments encoded as text
Supported output types
After decoding, base64app recognizes PDFs, images (PNG, JPEG, GIF, WebP, SVG), JSON and plain text, ZIP and Office documents, MP3/WAV audio, MP4 video, fonts, and other binary formats.
How it works
- 1. Paste your base64 string into the decoder above (data URIs are fine).
- 2. Leave auto-repair on if the string came from email, chat, or an API.
- 3. Click Decode — preview the result and download with the correct file extension.
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
How do I decode base64 online?
Paste the string into base64app and click Decode. The tool detects the file type, shows a preview when possible, and offers a download.
Can I decode base64 to PDF or images?
Yes. base64app auto-detects PDFs, PNG/JPEG/GIF/WebP/SVG images, and many other formats from the decoded bytes.
What if my base64 string is corrupted?
Enable auto-repair. base64app fixes padding, whitespace, data URI prefixes, URL-safe characters, and stray symbols before decoding.
Does decoding work without uploading?
Yes. Everything runs client-side. Your data never leaves your device.
What is the difference between standard and URL-safe base64?
URL-safe base64 replaces + with - and / with _. base64app converts URL-safe input automatically when auto-repair is on.
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.