LyAhn
3ee7d7a3ac
Single-file browser tool that decodes a base64 string and saves the result back out as a file. No server, no dependencies, nothing uploaded. Input cleanup covers data URIs, URL-safe alphabet, missing padding, line wrapping, percent-encoding and wrapping quotes. Type detection runs magic bytes (~30 signatures), then the data URI's declared MIME, then UTF-8 content sniffing for SVG/HTML/XML/JSON/PEM; unrecognised payloads fall back to .bin with a hex dump. Images, audio, video, PDF and text are previewed inline before download.
Base64 → File
A single-file web tool that decodes a base64 string and saves the result back out as a real file. Useful for pulling attachments out of API responses, log dumps, JSON payloads, config blobs and data: URIs without hunting for a working online decoder — and without pasting anything sensitive into someone else's website.
What it does
Open base64-decoder.html in any browser, paste the base64, and the decoded file appears on the right — type detected, previewed, ready to download.
Everything runs locally in the page. There is no server, no build step, no dependencies, and nothing is ever uploaded.
xdg-open base64-decoder/base64-decoder.html
Input handling
The input is cleaned up before decoding, so most real-world paste jobs work as-is:
| Input | Handled |
|---|---|
data:image/png;base64,iVBORw0... |
Prefix stripped, MIME type read from the header |
| Line-wrapped / indented base64 | All whitespace removed |
URL-safe base64 (- and _) |
Converted to standard + and / |
Missing = padding |
Restored |
Percent-encoded (%2B) |
URL-decoded first |
| Wrapping quotes from a JSON value | Trimmed |
Invalid input gives a specific reason — the offending character, or a truncated length — rather than a generic failure.
Type detection
The file type is worked out in three passes, in order of reliability:
- Magic bytes — ~30 signatures covering PNG, JPEG, GIF, WEBP, BMP, ICO, PDF, ZIP, GZIP, BZ2, XZ, 7z, RAR, TAR, MP3, MP4, MKV, OGG, FLAC, WAV, AVI, SQLite, TTF/OTF/WOFF/WOFF2, ELF, EXE and Java class files
- Data URI header — if the input was a
data:URI, its declared MIME type supplies the extension - Content sniffing — payloads that decode as valid UTF-8 are checked for SVG, HTML, XML, JSON, PEM and shell scripts
Anything unrecognised falls back to application/octet-stream and a .bin extension. The suggested filename is always editable before saving.
Preview
| Decoded type | Preview |
|---|---|
| Images | Rendered inline |
| Audio / video | Playable with controls |
| Embedded viewer | |
| Text-based | Syntax-free text view, plus a Copy text button |
| Anything else | Hex dump of the first 192 bytes with an ASCII column |
Shortcuts
- Drag and drop a
.txt/.b64file onto the input to load its contents - Ctrl/Cmd + S downloads the decoded file
- Enter in the filename field downloads immediately
Requirements
Any modern browser. Works straight from file:// — no web server needed.
The Paste button uses the clipboard API, which some browsers restrict on file:// pages; if it does nothing, use Ctrl+V in the input instead.