Apparently CodePen 2.0 sends data to their servers as you type

maxim-fin · 2026-09-07T11:22:40.000Z

They send all typed into editor input to codepen.dev almost immediately (you would see in 1-2 sec after you typed your secret that it appears in respective Network/Response tab) even before one saved it. I tested this with a unique marker: after typing it into index.html, CodePen ran a build with "save:false", and the marker then appeared verbatim in the HTML served from the generated "*.codepen.dev preview". Thus, if you ever entered some secrets in there by mistake consider them compromized even if you did not publish/save the pen

giancarlostoro 13 days ago |

Pretty sure it always autosaved so this makes sense to me? I always assume it would send my data over to their backend, its code that ends up there regardless?

maxim-fin 12 days ago | |

Yes, that is for autosave and for rendering

Edit: The point is that any secrets typed/pasted in there should be considered compromized

giancarlostoro 12 days ago | | |

I don't know why anyone would paste or type secrets into codepen which is public by default... But it always seemed like it auto-saved / sent your code over to the back-end, going back ten years roughly?

traviswingo 12 days ago | | |

Copy -> paste -> redact secrets

That flow would be considered unsafe, and probably common.

leptons 12 days ago | | |

It's also a foolish thing to do. Any time anyone types anything into anywhere on any webpage, that data is as good as gone, it's out there. Back in the 90's I experimented with per-character logging on all form input boxes, just because I could. That's still possible today.

maxim-fin 12 days ago | | |

This is exactly the scenario I pictured

giancarlostoro 12 days ago | | |

If you are pasting secrets into codepen you are probably really terrible at all other basic security practices.

midnitewarrior 13 days ago |

Look into https://www.fullstory.com/ , many major websites use this, it's basically a real-time video view of the user's browser screen. You can see where they move their mouse, how quickly they are typing, each character one at a time.

I worked for a company that would have phone support for users, and we'd be watching their screens giving gentle suggestions to them as they were using our app for how to do what they needed to do. We never offered up what we were doing, but given users' poor descriptions of what they were doing, FullStory was an amazing customer service tool.

VoidWhisperer 13 days ago | |

Something like this would've been incredibly useful at my previous job - we often had to put together how a user triggered an issue using a combination of logs and analytics to track what actions they took..

giancarlostoro 13 days ago | |

Elastic has something like this too, as does Splunk iirc. Idk how all three compare I just know they can track DOM events type of stuff and recreate a flow video.

maxim-fin 13 days ago | |

interesting!

tvink 13 days ago |

You're gonna be shocked how many input fields do this for various UX features :)

nusl 13 days ago | |

Shopify does this. If you ever go to purchase a product on a Shopify 'site, and enter eg your e-mail address, it'll save it even if you decide to cancel and close the tab. Sometimes you receive spam from companies along the lines of marketing or "we noticed you didn't complete your purchase" type crap. Shit is rly invasive.

davidmurdoch 13 days ago | | |

They can only send the marketing emails if you have the "send me marketing emails" checkbox checked when you type in your email address. Dark pattern, yeah.

xingped 12 days ago | | |

That has never stopped companies from spamming me with marketing even when I didn't agree or even explicitly disagreed (unchecked). Not a single company has been or ever will be held accountable so they just keep doing it.

davidmurdoch 12 days ago | | |

Shopify 's "abandoned cart" emails are legally considered transactional emails, not marketing, which is probably what you're getting. It's a feature built in to Shopify. If the email isn't related to your abandoned cart contents, you can report it to Shopify. Shopify will investigate reports of abuse and eventually will terminate a store account for blatant abuse.

nusl 12 days ago | | |

No, I've received it just from entering my e-mail and nothing else. So many companies don't care, or don't know.

Either way, if I enter my e-mail, decide "nah" and quit, that should be that. It shouldn't be sending my details in the background

davidmurdoch 12 days ago | | |

The checkbox is usually checked by default (it's a Shopify setting), in many jurisdictions (like the USA). "It" was probably an "abandoned checkout" email, which is a transactional email, and is legally allowed.

I use this Shopify feature as a buyer to get discount codes, as abandoned cart emails often come with them.

aveao 12 days ago | | |

Isn't the email at the top of the form and the marketing checkbox at the bottom? It's an awful dark pattern and makes me want to not use any company that uses shopify.

They require your full address to show you shipping prices as well (vs just letting you estimate with country and postal code alone), so I have to punch in a ton of details before I nope out at awful shipping costs, and I end up with these emails.

davidmurdoch 12 days ago | | |

No. For Shopify's checkout, it's directly beneath the email input.

You're probably getting the "abandon cart" emails, which is legally considered a "transactional email", and doesn't require consent.

weezing 13 days ago | | |

Simplelogin is a godsend for this cancer

Boss0565 13 days ago | | |

Have you checked to see if it’s stored in localstorage

masfuerte 13 days ago | | |

If they are sending you emails the address is not just in localstorage.

embedding-shape 13 days ago | |

HotJar and similar services are (were?) popular as well, and those record your mouse pointer movements and clicks as well, then displays that as an overlay over the application, so it's essentially a "screen recording" of your session of the application.

maxim-fin 13 days ago | | |

Not sure if they are still popular but in the past they may have really slowed down the site

glub 13 days ago | | |

Now it's an entire industry. They call it "bot protection"

crisnoble 12 days ago | | |

Wait until you see a microsoft clarity recording.

maxim-fin 13 days ago | |

Yes, but codepen is for frontend devs. And devs are more likely to accidentally leak secrets because, well, they have them

Edit: accidantlay -> accidentally

millerm 12 days ago |

Reddit does this. Every keystroke you type into a comment box is sent back to them. So, that means even if you decided to cancel posting something, they still receive what you wrote. I have been known to write responses that were harsh and angry, and I simply don't send. Sometimes it's therapy for me to think through something while typing whatever is in my head. Then I go back and edit once I have have thought it through. I don't want that info sent back. So, I tend to not involve myself with much online anymore. I don't want to expose myself to the thought police.

I find the browser the most unsafe piece of tech deployed.

c-hendricks 12 days ago | |

Ever since I learned about full story / datadog RUM I've been writing my replies in a notes app then copy and pasting back in the browser

millerm 12 days ago | | |

Yeah, it's infuriating.

maxim-fin 13 days ago |

CodePen does not disclose this in neither ToS nor in Privacy Policy, only in Builds documentation they say: “As you work on CodePen, your Pens are constantly running through the CodePen Compiler”

nseskin 13 days ago |

There’s a detailed discussion of the same issue here https://www.reddit.com/r/webdev/comments/1rj1oac/i_planted_f...

maxim-fin 13 days ago | |

Indeed, it looks like CodePen v1 was sending data to codepen.io, cpwebassets.codepen.io, and cdpn.io. Now v2 sends to codepen.dev

kypro 13 days ago |

This is so it can restore any unsaved changes.

I take no opinion on whether this is good or bad, but I can see how from a UX perspective it's nice not to lose 10 minutes of work because your browser crashes or something.

maxim-fin 13 days ago | |

Yes, absolutely, there are good reasons for that. The point is that any secrets typed/pasted in there should be considered compromized

Edit: but then if you you quit (or crash) without saving the pen first there is no way to recover unsaved work regardless. That is, the pen must be saved manually at least once for the user to benefit from the autosave.

phyzome 12 days ago | | |

Secrets pasted into any web page should be considered compromised.

mkgiga 12 days ago | | |

please don't paste credentials into codepen

eitri 8 days ago |

Autosave doesn't necessarily require the server though. localStorage can provide keystroke level saving on the client and survive a crash just fine. So I'm not sure that "its just autosave" fully explains why every keystroke needs to be sent to the server.

keepo404 13 days ago |

because this is how autocomplete logic works i guess? Frontend cannot guess language and completions for you

mkgiga 12 days ago | |

yes it can. all you need are some tokenizers for the languages you want to guess and once you derived the language, a few lookup tables to store variable name references in :)

giancarlostoro 13 days ago | |

Yeah I remember CodePen refreshing for me plenty of times.

maxim-fin 13 days ago | |

No autocomplete involved there.

embedding-shape 13 days ago | |

Well, except for the cases when you happen to have the entire VM for your language running in the same tab where you program lives, and they both are all JS.

Probably harder, and wouldn't work equally well for everyone, but it would be possible to have "guess language and autocomplete" entirely client-side, especially when it comes to JavaScript of all languages.

odo1242 13 days ago | | |

It seems like the main disadvantage would be that you have to load all the autocomplete data / model weights on the client-side and your webpage might be CPU/memory limited

embedding-shape 13 days ago | | |

> main disadvantage would be that you have to load all the autocomplete data / model weights on the client-side

Not sure what "model weights" you're talking about, but yes, that is the trade-off. Although complete autocomplete data for the entirely of the JavaScript APIs would be what, in an efficient format, easily below 1MB at least.

mkgiga 12 days ago | | |

Code editor autocomplete doesn't use ai — search up LSP

cph123 13 days ago |

For basic previewing I like to use https://htmledit.squarefree.com which has been online for years and does it all client side.

dbushell 12 days ago |

I'm looking forward to the Gamers Nexus exposé

bashy 13 days ago |

Sent to them to render the preview pane. Same as pasting secrets anywhere on a browser.

Wait until you find out copying content on a computer might sent it over Wi-Fi/Bluetooth for sharing on other devices.

maxim-fin 13 days ago | |

Yes, that is for rendering Edit: and as "kypro" pointed out also for saving the current work but if you you quit (or crash) without saving the pen there is no way to recover unsaved work regardless

mkgiga 12 days ago |

if you paste secrets in any website you should be fired immediately

pdyc 13 days ago |

i made my own html playground that is browser only and shares preview via url hash because of these useless shenanigans of codepen, its not as featureful but i mostly use it for sharing single page html files

https://easyanalytica.com/tools/html-playground/

spartanatreyu 9 days ago |

Well duh, this is how codepen works!

Try this:

1. Open one of your codepens

2. Now open the same codepen in a different window so you have two open at the same time

3. Now type in one window

4. Watch it s̶e̶n̶d̶ ̶y̶o̶u̶r̶ ̶c̶h̶a̶n̶g̶e̶ ̶t̶o̶ ̶t̶h̶e̶ ̶s̶e̶r̶v̶e̶r̶ ̶t̶o̶ magically update all other clients

---

Also, notice how your browser never had to download typescript, sass, babel, tailwind, etc...?

That's because what you type gets sent to the server to transform it into compiled html.