Selfhosted

I mean... It's decoding into garbage because you're feeding it more than just the base64 section. I suppose if you're already running nginx or something you could easily make a page that uses javascript to break the link down (possibly using /, ?, = as separators) and decode sections that look like base64. If you make it javascript and client side there's not really any privacy concerns.

EDIT: Oops. My Lemmy client didn't load the other replies at first, I didn't realize you already had plenty of other options.

There is no such thing as a base64 encoded url. Part of an url might hold base64 encoded data, but never the url itself.

These online tools aren't working because you're using them wrong.

It’s 3 lines of code in basically every programming language, no need for selfhosting, just open the terminal?

That url isn’t base64 encoded. You can tell by the fact that it’s still a URL, and doesn’t decode……

Don't include the non-encoded part of the data or it will corrupt the decryption. The decoder can't tell the difference between data that's not encoded and data that is encoded since it's all text.

There's base64 -d on the command line.

Cyberchef!

I wrote this little webapp thing some time ago. It's not exactly what you asked for but is a good example.

All it does is base64 encode a link and adds the server url in front of it. When someone visits that link it will redirect them to the destination. The intent is to bypass simple link tracking / blocking in discord and other platforms.

There are also checks for known bad domains and an attempt to remove known tracking query parameters.

https://git.tsps-express.xyz/liliumstar/redir

Edit: I forgot to add it also blocks known crawlers (at least at time of writing) so that they can't just follow the 302 and figure out where it goes.

I have nothing to add except the appreciation for everyone who helped and amazement at the vastly differing ways people produced working results.

There's something else going on there besides base64 encoding of the URL -- possibly they have some binary tracking data or other crap that only makes sense to the creator of the link.

It's not hard to write a small Python script that gets what you want out of a URL like that though. Here's one that works with your sample link:

#!/usr/bin/env python3

import base64
import binascii
import itertools
import string
import sys

input_url = sys.argv[1]
parts = input_url.split("/")
  
for chunk in itertools.accumulate(reversed(parts), lambda b,a: "/".join([a,b])):
  try:
    text = base64.b64decode(chunk).decode("ascii", errors="ignore")
    clean = "".join(itertools.takewhile(lambda x: x in string.printable, text))
    print(clean)
  except binascii.Error:
    continue

Save that to a file like decode.py and then you can you run it on the command line like python3 ./decode.py 'YOUR-LINK-HERE'

e.g.

$ python3 ./decode.py 'https://link.sfchronicle.com/external/41488169.38548/aHR0cHM6Ly93d3cuaG90ZG9nYmlsbHMuY29tL2hhbWJ1cmdlci1tb2xkcy9idXJnZXItZG9nLW1vbGQ_c2lkPTY4MTNkMTljYzM0ZWJjZTE4NDA1ZGVjYSZzcz1QJnN0X3JpZD1udWxsJnV0bV9zb3VyY2U9bmV3c2xldHRlciZ1dG1fbWVkaXVtPWVtYWlsJnV0bV90ZXJtPWJyaWVmaW5nJnV0bV9jYW1wYWlnbj1zZmNfYml0ZWN1cmlvdXM/6813d19cc34ebce18405decaB7ef84e41'
https://www.hotdogbills.com/hamburger-molds/burger-dog-mold

This script works by spitting the URL at '/' characters and then recombining the parts (right-to-left) and checking if that chunk of text can be base64 decoded successfully. If it does, it then takes any printable ASCII characters at the start of the string and outputs it (to clean up the garbage characters at the end). If there's more than one possible valid interpretation as base64 it will print them all as it finds them.

IT-Tools is kind of fun: a web page full of common tools, converters, references, cheat sheets, etc.

Use a bash command line:

https://stackoverflow.com/questions/6250698/how-to-decode-url-encoded-string-in-shell

https://addons.mozilla.org/en-US/firefox/addon/redirect-bypasser-webextension/ in desktop Firefox seems to work for your link. For mobile there might be apps that you share the link to and they dissect it, but a very quick search didn't turn up anything.

CorentinTh/it-tools does that and a lot more

Try https://flathub.org/en/apps/me.iepure.devtoolbox