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

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.

The encoding format of URLs is URL encoding, also known as percent-encoding. Content in the URL may be first encoding in some other format, like JSON or base64, and then encoded additionally using percent-encoding.

While there is a standard way to decode percent-encoding, websites are free to use base64 or JSON in URLs however they wish, so there’s not a one-size-fits-all way to decode them all. For example, the “/” character is valid in both percent-encoding and base64-encoding, so to know if it’s part of a base64-encoded blob or not, you might end up trying decoding several parts of the URL as base64 and checking if the result looks like URL-- essentially brute force.

A smarter way to do this might be to maintain a mapping between your favorite sites that you want to decode and what methods they use to encode links. Then a tool could efficiently directly decode the URLs embedded in these click trackers.

Just take the base64 bit of the url. The whole url isn’t a base64, so it decoded to garbage.

The base64 bit decodes just fine.

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.

CorentinTh/it-tools does that and a lot more

Not that you should vibe code, but you could vibe code this so easily. Have it output a static website. Give the source code a scan if you’re paranoid. Check the network tab if you’re really really paranoid. But literally you could have it output this as a static index.html file that you drop into your browser of choice.

This is the only type of coding LLMs should ever be used for imo. A small, very clearly defined task that is very easy to verify if it works. And code that won’t infect a larger project.

Edit: as others pointed out, that url isn’t base64 encoded. You would have to clearly define what you are trying to do if you want this to work. For example, do all urls follow the same format as the above?

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

Use a bash command line:

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

Cyberchef!

There’s base64 -d on the command line.

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.

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

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.

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.