Selfhosted

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.

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.

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 base64 -d on the command line.

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

Cyberchef!

I've been working on a URL cleaning tool for almost 2 years now and just committed support for that type of URL. I'll release it to crates.io shortly after Rust 1.90 on the 18th.

https://github.com/Scripter17/url-cleaner

It has 3 frontends right now: a CLI, an HTTP server and userscript to clean every URL on every webpage you visit, and a discord bot. If you want any other integration let me know and I'll see what I can do.

Also, amusingly, you decoded the base64 wrong. You forgot to change the _ to / and thus missed the /burger-dog-mold and tracking parameter garbage at the end. I made sure to remove the tracking parameters.

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

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

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 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.

Use a bash command line:

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

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

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.

CorentinTh/it-tools does that and a lot more

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.

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