Base64
Decoder
Decode Base64 strings to text or images instantly. Supports data URIs and plain Base64.
How It Works
Paste Base64
Paste a Base64 string or data URI into the input field.
Auto-Decode
The content is decoded live as you type. Images are previewed automatically.
Copy or Download
Copy the decoded text or download the decoded content.
Decode Base64 strings online back to plain text, JSON, or images, with automatic detection of data URIs. ConverterUp's Base64 decoder is useful for inspecting JWT payloads, debugging API responses, decoding email attachments, and extracting embedded images from CSS or HTML. Paste the encoded string, see the result instantly, and copy the text or download the decoded image. The decoding runs entirely in your browser, so sensitive tokens, customer payloads, and private images never get logged or transmitted to a remote server.
Frequently asked questions
Does it decode JWT tokens?
It decodes the Base64URL parts, which is exactly what JWT uses for header and payload. Paste the full token and ConverterUp displays the JSON header, JSON payload, and signature segment for inspection.
What is the maximum input size?
Up to 25 MB of encoded text. Decoded output is roughly 75 % of that size since Base64 inflates content by about a third.
Can it detect images automatically?
Yes. If the decoded bytes start with a known image header (PNG, JPG, GIF, WebP) or the input is a data URI, the tool shows a preview and offers a download button alongside the raw text view.
Is the input sent to a server?
No. All decoding happens client-side using the browser's atob and TextDecoder APIs. ConverterUp does not have an endpoint that receives Base64 strings, which matters when the encoded data contains credentials.