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▲Introduction to AT Protocolmackuba.eu
173 points by psionides 19 hours ago | 92 comments
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sedatk 16 hours ago [-]
Here is an excerpt from the offical docs for the curious:

"Why not use ActivityPub?

ActivityPub is a federated social networking technology popularized by Mastodon.

Account portability is a major reason why we chose to build a separate protocol. We consider portability to be crucial because it protects users from sudden bans, server shutdowns, and policy disagreements. Our solution for portability requires both signed data repositories and DIDs, neither of which are easy to retrofit into ActivityPub. The migration tools for ActivityPub are comparatively limited; they require the original server to provide a redirect and cannot migrate the user's previous data.

Another major reason is scalability. ActivityPub depends heavily on delivering messages between a wide network of small-to-medium sized nodes, which can cause individual nodes to be flooded with traffic and generally struggles to provide global views of activity. The AT Protocol uses aggregating applications to merge activity from the users' hosts, reducing the overall traffic and dramatically reducing the load on individual hosts.

Other smaller differences include: a different viewpoint about how schemas should be handled, a preference for domain usernames over AP's double-@ email usernames, and the goal of having large scale search and algorithmic feeds."

hiena03 15 hours ago [-]
Relevant post by Christine Lemmer-Webber (Co-creator of ActivityPub) https://dustycloud.org/blog/how-decentralized-is-bluesky/
verdverm 15 hours ago [-]
a very opinionated piece that leads by conclusion rather than building up to it.

The main part of ATProto that is centralized is the PLC and that will eventually be made (most likely) into a consortium. PDS hosting is debatable

That being said, it should be possible to run completely independent atproto networks today. We have several dev infra setups for doing it in the ecosystem

dokyun 13 hours ago [-]
> it should be possible to run completely independent atproto networks today

But does anyone do it? It doesn't really matter if it's /theoretically possible/ if no one actually does it.

Running an ActivityPub server is piss easy, anyone can do it on a $5 VPS or in their basement, and that's one of its big strengths.

poink 8 hours ago [-]
BlackSky seems to be run by a competent dev with a high enough profile that I see his posts regularly without following him directly

Based on his progress posts it seems that ATproto is intentionally moving in the right direction and BlackSky has progressed to the point he’s asking for volunteers to move off Bluesky and try out his implementations

danabramov 12 hours ago [-]
People are doing it yeah. The post linked in the comment above is already outdated, see https://whtwnd.com/bnewbold.net/3lo7a2a4qxg2l for relatively recent developments.
runako 12 hours ago [-]
I could be mistaken, but I believe BlackSky is pretty close today.
nulfrost 12 hours ago [-]
> Running an ActivityPub server is piss easy, anyone can do it on a $5 VPS or in their basement, and that's one of its big strengths.

same statement can be applied to running a bluesky PDS. Here are the server recs: https://github.com/bluesky-social/pds?tab=readme-ov-file#sel...

ludicrousdispla 7 hours ago [-]
I am finding it very informative.
BobbyTables2 13 hours ago [-]
Was fully expecting to see descriptions of “ATD” and “ATH”…
donatj 5 hours ago [-]
Yes, exactly! I was expecting https://en.wikipedia.org/wiki/Hayes_AT_command_set
bobmcnamara 12 hours ago [-]
RING, RING, RING, ATA, CONNECT!
snvzz 9 hours ago [-]
+++ATH0
verdverm 17 hours ago [-]
If you are interested in building on ATProtocol, one of the best places to start is the Discord (until we have an atproto native alt @blebbit.app)

https://discord.atprotocol.dev/

Of course the spec is good too, very easy read

https://atproto.com

https://docs.bsky.app

namrog84 3 hours ago [-]
When discord alternative?
tomrod 17 hours ago [-]
What sorts of things can be built on the protocol?
mozzius 17 hours ago [-]
It’s good at social-oriented apps - there’s obviously Bluesky, and many other smaller apps in the style of other platforms.

One of the most interesting projects is tangled.sh - a github-like using atproto for the social layer, which fits perfectly.

psionides 17 hours ago [-]
Anything "social" basically - the first ideas that come to people's minds are of course things like: GitHub but on ATProto, Instagram on ATProto, Tiktok on ATProto, Reddit on ATProto…
jazzyjackson 16 hours ago [-]
Why isn't there a Discord built on ATProto ? [Serious Question, wondering if there are trade-offs that make this especially annoying]
OneDeuxTriSeiGo 16 hours ago [-]
Currently atproto is still figuring out how to approach private data. Right now there exists extremely limited abilities to store private data via the bluesky preferences but until that mechanism is standardised in a way other projects can use, there's not really a good way to store data privately let alone transmit data privately.

There's a working group for doing this but it'll be a while before anything is adopted at scale.

If fully public is okay for you, there is actually already a chatroom/IRC-esque platform called Roomy. It works well but it is all public and there's a touch more latency than a normal client-server platform due to the nature of atproto's gossip protocol.

psionides 16 hours ago [-]
So, one big problem is that there's basically no way to have shared-private data in the protocol - it's either private to you, or fully public. Hence no "locked accounts", "followers-only posts" and so on on Bluesky, and this also prevents more sensitive ideas like e.g. "Strava on ATProto" (where you probably don't want to share your run map with the whole world!).

They are working on this, but it's still gonna take a while as I understand.

jazzyjackson 16 hours ago [-]
Ah thanks for the answer. What's the PKI story on bluesky, doesn't every identity have a corresponding public key? So if I had a list of people I wanted to a post to be visible to, couldn't I "just" encrypt it with a key that is decryptable by each of those individuals via their pubkey?
verdverm 16 hours ago [-]
PKI distribution for encrypted data is an unsolved problem at the scale of many millions or billions of people. Signal caps at 10k iirc

It's also generally not advisable to make your cypher text publicly visible

That being said, I'm working with others in the ecosystem on "permissioned space", which are much closer to how people think about Google Docs and similar systems working.

There is also another effort around E2EE content (MLS) for messaging. They are also thinking beyond just messages too

ianopolous 9 hours ago [-]
Peergos has a private data solution that is compatible with (and predates) atproto (dag-cbor, portable data and accounts and social graph).
tomrod 14 hours ago [-]
Fantastic. Looking forward to seeing where you land.
psionides 16 hours ago [-]
I'm not really familiar with that layer of things, but I think it's possible, though that "just" is doing a lot of work here of course, and I think it might not necessarily be a good idea to have encrypted messages available publicly for everyone all the time, so they can collect them and wait until someone slips up / a vulnerability is found / they have enough hardware to crunch it...
kristo 16 hours ago [-]
It’s not that shared private data is impossible, just that the mechanisms haven’t been fleshed out yet. I expect this type of setup might be difficult to scale?
actionfromafar 16 hours ago [-]
My immediate thought to
verdverm 16 hours ago [-]
Working on it, https://blebbit.app (mainly landing pages, but login and basic chat work)
beepbooptheory 14 hours ago [-]
Thats such a bummer, I was on the matrix dev chat for a while and it was good and helpful. I wonder why they changed it from that?
psionides 13 hours ago [-]
I don't think that Matrix chat was used much after the initial months, I've only really heard about it in legends... That Discord (the ATProto Touchers) is community-run.
xphos 15 hours ago [-]
Here I was thinking I'd see old AT commands for controlling radios. Learned something new
sitzkrieg 13 hours ago [-]
theyre not old and still used in many many cell modems :-)
xbar 13 hours ago [-]
Yup.

Bluesky's name collision was pretty avoidable here but I guess they thought the obvious name was BS.

dunham 14 hours ago [-]
I believe that's still used in phones for communication between the computer and the cell phone hardware.
thesuperbigfrog 14 hours ago [-]
ATDT <My Favorite BBS>

. . .

ATH

slyrus 14 hours ago [-]
Same. ATS11=43 was magic back in the day.
chrismorgan 8 hours ago [-]
> unicode scalars, which most languages index strings in

Very few do. Of moderately popular languages, Python is the only one I can think of. Well, Python strings are actually sequences of code points rather than scalars, which is a huge mistake, but provided your strings came from valid Unicode that doesn’t matter.

Languages like Rust and Swift make it fairly easy to access your string by UTF-8 or by scalar.

Languages like Java and JavaScript index by UTF-16 code unit and make anything else at least moderately painful.

> This is somewhat of an unfortunate tech debt thing as I understand, and it was made this way mostly because of JavaScript, which doesn’t work with UTF-8 natively. But this means you need to be extra careful with the indexes in most languages.

I’m confused here. You established indexing is by UTF-8 code unit, then said it’s because of JavaScript which… doesn’t do UTF-8 so well? If it were indexed by UTF-16 code unit, I’d agree, that’s bad tech debt; but that’s not the case here.

Bluesky made the decision to go all in on UTF-8 here <https://docs.bsky.app/docs/advanced-guides/post-richtext#tex...>—after all, the strings are being stored and transferred in UTF-8, and UTF-8 is increasingly the tool of choice, and UTF-16 is increasingly reviled, almost nothing new has chosen it for twenty years, and nothing major has chosen it for ten years, it’s all strictly legacy. Hugely popular legacy, sure, but legacy.

dom96 17 hours ago [-]
ATProto is a lot of fun to work with, but of course by no means perfect. The biggest challenge right now is dealing with private data, I hope they can figure out a way to support it soon.
verdverm 17 hours ago [-]
see my comment in another thread, things are happening!
trollied 16 hours ago [-]
+++ATH0

Those old enough will know :)

voxadam 16 hours ago [-]

   NO CARRIER
dd_xplore 15 hours ago [-]
I bought a 5G modem made by waveshare, I had lot of fun tinkering that device with AT commands.
esseph 16 hours ago [-]
Thinking about changing my ring tone now... ;)
donpdonp 12 hours ago [-]
ATDT1170,
jeffreygoesto 16 hours ago [-]
AT&N34 ha!
tomgag 7 hours ago [-]
I didn't write this for the HN crowd, but here we go anyway: https://gagliardoni.net/#20250818_battle_of_socials

Happy to correct any factual inaccuracies.

leshokunin 18 hours ago [-]
Been pondering for my team to use it for our product’s timeline. I don’t particularly want our user base to be Bluesky, but it’d be good to have support for the protocol, and control over the system.

Have there been any products go embraced this? Or is it like ActivityPub where basically the whole thing is Mastodon.

troyvit 1 minutes ago [-]
Similarly our news site is considering a live-blog feature and I'm wondering if AT Proto would be a fun way to do it.
gargron 17 hours ago [-]
ActivityPub is embraced by:

  - Threads  
  - Flipboard  
  - WordPress  
  - micro.blog  
  - NodeBB  
  - PeerTube  
  - Pixelfed  
  - GoToSocial  
  - Akkoma  
  - ...and countless smaller projects
It is by no means just Mastodon.
rmccue 15 hours ago [-]
> WordPress

This isn’t quite true. WordPress.com announced they were planning on ActivityPub support, but that is a separate entity run by a commercial company (Automattic).

Their plan was to support it specifically on Tumblr, as well as helping fund an open source plugin for it; there have been no plans to integrate it into the WordPress software directly.

I believe they’ve also deprioritised it as they did significant layoffs recently.

pera 5 hours ago [-]
What do you mean? WordPress already supports ActivityPub through their plugin:

https://wordpress.org/plugins/activitypub/

I follow a few blogs on Mastodon just fine (for example John Carlos Baez's Azimuth, https://johncarlosbaez.wordpress.com/), it's just like an RSS reader in your timeline.

leshokunin 3 hours ago [-]
My point is in terms of activity. I’m familiar with all those services. I recommend doing a percentage of each vs total activitypub content.

I would also discard services that auto post to the fediverse but are not actively used by the majority of users as such.

16 hours ago [-]
ethan_smith 10 hours ago [-]
Beyond Bluesky, there's a growing ecosystem including Pebble (a self-hosted PDS), Skychat (messaging), Skeet (app framework), Graysky (mobile client), and several specialized feeds/algorithms - unlike ActivityPub, ATProto's architecture allows for more diverse application types while maintaining interoperability.
leshokunin 3 hours ago [-]
Do you have experience with Pebble? Could be nice to have a ready made pds!
psionides 18 hours ago [-]
For now mostly just small things that the Bluesky dev/user community is playing with, but check out e.g. Tangled which is meant to be a GitHub alternative on ATProto: https://tangled.sh
verdverm 17 hours ago [-]
TikTok: https://bsky.app/profile/skylight.social

Insta: https://bsky.app/profile/pinksky.app

Twitch: https://bsky.app/profile/stream.place

Events: https://bsky.app/profile/smokesignal.events

verdverm 16 hours ago [-]
Build your own feeds / algorithms in the browser: https://graze.social
dom96 17 hours ago [-]
Pinterest: https://bsky.app/profile/scrapboard.org
ihndan 17 hours ago [-]
And here is an app to generate unified feed for such apps: https://bsky.app/profile/atpage.one
sitzkrieg 13 hours ago [-]
activitypub is mostly used in the fediverse. mastodon is one of many clients and servers, and one of the worst.
selimnairb 3 hours ago [-]
Was hoping that BlueSky somehow used the AT command set.
nate_nowack 17 hours ago [-]
would love fb marketplace disruptor on atproto
mdaniel 15 hours ago [-]
Isn't the problem the network effect, and not the protocol whatsoever?
nate_nowack 13 hours ago [-]
yea i dont think there's any blocker from a protocol perspective, im just saying i'd love to see it happen. adoption for sure among the largest hurdles id guess
Cyberdog 4 hours ago [-]
Retvrn to Craigslist.
verdverm 17 hours ago [-]
Here's another great resource about the ATProto distributed design

https://atproto.com/articles/atproto-for-distsys-engineers

chombier 6 hours ago [-]
That was a nice read, thanks.
wyldfire 17 hours ago [-]
I'll save you a click: it's unrelated to the Hayes AT commands [1].

[1] https://en.wikipedia.org/wiki/Hayes_AT_command_set

mrheosuper 8 hours ago [-]
I was expecting the old AT protocol i use to communicate with Radio module
don_searchcraft 18 hours ago [-]
Would love for more platforms to embrace the AT protocol.
verdverm 17 hours ago [-]
I'm working with some people on permissioned spaces for atproto (spec and pds changes). This will unlock a ton of use-cases not possible today

Working Group is forming this fall, we'll be at IETF, Montreal in Nov

Also building one such platform that needs permissioned spaces, if you want to follow along

https://github.com/blebbit/atproto

https://bsky.app/profile/blebbit.app

Off the top of my head, there are also WGs for E2EE messaging, web monetization, and geo.

Lot's of infra getting built this year

acheron 17 hours ago [-]
In this house, we believe “AT protocol” refers to Hayes modem commands.

ATDT2024561414

imoverclocked 16 hours ago [-]
A slightly more modern usage for cell modems that still implement AT commands in 2025:

AT+QSINR?

AT+QRSRQ

AT+QRSRP

AT+QNWINFO

-- getting current status/band of a link

JdeBP 16 hours ago [-]
I see the error of forgetting the long distance prefix and dialling some poor innocent to squeal tones in xyr ear during Zone Mail Hour is alive and well. (-:
Angostura 17 hours ago [-]
+++ ATH0
imoverclocked 16 hours ago [-]
This brings back memories of hanging my 56k modem up with a specially crafted ping command :)
blainsmith 17 hours ago [-]
If you want to find other apps that are using Bluesky and ATProto we run https://blueskydirectory.com for that. Feel free to add any apps you find to it!
koolala 18 hours ago [-]
Would be great to have a new modern alternative to the E-mail standard that is usable for both public and private messaging.
gargron 17 hours ago [-]
ActivityPub can be used for both public and private messaging, though I don't think the e-mail standard needs to be retired anytime soon.
JdeBP 16 hours ago [-]
There was once an idea named IM2000.

Then the world invented pull-style electronic communications systems via another route. You're looking at one.

* https://news.ycombinator.com/item?id=10410164

* https://jdebp.uk/Proposals/IM2000/

verdverm 17 hours ago [-]
We might be able to do this with permissioned spaces. There are instances or use-cases where you want an outside entity to make changes to a user's repo

- email / inbox [or @mail since it is @atproto :]

- unsubscribe from email

- notifications / rsvp

The cool thing is that we could use the stackable moderation infra for dealing with bad actors

https://bsky.social/about/blog/03-12-2024-stackable-moderati...

jazzyjackson 16 hours ago [-]
stackable moderation for ignoring senders is a cool idea. I'll keep an eye out for permissioned spaces, is there encryption and signatures involved at all? (everything on bluesky is signed with PKI, iirc?)

And just unsolicited feedback but "Blebbit" is a deeply terrible name. It turns my stomach for some reason. I don't even know what a bleb could be or what it could represent besides, like, an ulcer.

verdverm 16 hours ago [-]
Your content is signed with a key, but there isn't PKI in the same sense as certificates

There are two efforts around "permissioned" and "encrypted" spaces/content, where encrypted is the E2EE / signal like stuff and permissioned is more like Google Docs or the Discord like permissioning systems. There are use-cases for both

re: name, the second person to dislike, outnumbered by those who do like, will add you to the tally

the name is a play on plebeians / plebs / blebs, not to belittle, but to emphasize this is for the people, not the oligarchs.

Credible Exit Philosophy is important to me and the ATProtocol ecosystem. It means that users can leave an app without losing their data, that they can move their database without losing access, that the majority of Bluesky users could switch to an alternative if they become adversarial.

What it means is that ATProtocol bakes competition into our shared social fabric that all apps build on

jazzyjackson 17 hours ago [-]
email has come a long way with SPF, DKIM, and DMARC, and its cool that anyone can purchase a slice of the global namespace that is transferable between providers, but AFAIK the biggest road block to using email in a distributed self sovereign way is reputation and getting your messages delivered to google and outlook users partially because of the nonstop spam.

Do we have any new tools to prevent spam in a post-email world? Or can we just use the current email structure with some better GUI around PGP and Hashcash and force anyone who wants to send a message to burn 10 cents worth of electricity ?

I'm curious what you're looking for in an email standard ?

fluoridation 17 hours ago [-]
A quick back-of-the-envelope calculation says that USD 0.1 would be about 700 Wh, so, give or take, a high-performance desktop processor running full tilt for over four hours.

Personally, I'd prefer something like an expansion of how XMPP works. By default you only see what people in your contact list have sent you, and anything else is marked "dubious", and it's up to you to read it or not. I think it's a mistake that email servers have been given the responsibility to filter unwanted traffic. Email servers should have only ever simply passed along whatever they received (excluding excessively large messages, of course).

oever 4 hours ago [-]
> By default you only see what people in your contact list have sent you, and anything else is marked "dubious", and it's up to you to read it or not.

Any email client could implement this policy. You could even prioritize mail over who sent it or whether it's a reply to a mail you sent or have already read.

fluoridation 8 minutes ago [-]
Yes, but if the third server down the line didn't propagate the email, there's not much the client can do. That's what sucks about email as a protocol; it's been taken over by a handful of providers who will refuse to play ball with anyone outside their club, or who doesn't have the time to monitor the continuously-updated black lists.
JimDabell 7 hours ago [-]
There’s a fairly direct route to solving this with email. The problem that needs to be solved is that knowledge of an email address is the only thing needed to send to it. Introducing recipient consent as an additional requirement solves spam and phishing.

The first email a sender sends to a recipient has an attachment that serves as a request to email them for a specific purpose (e.g. human:human, mailing list, transactional). This email is not delivered to their inbox immediately, but to a separate “friend request” style queue. When the recipient approves, the sender receives a Biscuit token [0] and the email is delivered to the inbox.

Subsequent emails are sent by attenuating a one-time-use token from the master token, which is included in a header. Because they have verifiable authorisation, this can skip all existing spam heuristics because the receiving mail system knows for certain the recipient authorised this sender.

Biscuits can also be attenuated to reduce scope. Want the hotel you are staying at to only be able to send you email for the next 30 days? No problem. Mailing list providers can reject tokens that are scoped to transactional email. A sender can reduce blast radius of compromises by attenuating new tokens to give to third-party providers.

Authorised senders who spam can have all their historical emails quarantined at once and their ability to send in the future removed. Recipients can see who gave spammers their email address.

People who send mail are incentivised to implement this because it improves delivery rates by bypassing all existing spam filters, including IP reputation. “Ask for a token and you’ll never hit a spam filter again” is something a lot of people would jump at the chance for. No need for providers like Mailchimp, you could go back to sending mail directly from your own servers.

Recipients are incentivised to implement this because it will cut down on spam and phishing significantly.

This can be implemented independently of the other side because the fallback situation is the status quo – the initial email just has an attachment that goes ignored, and subsequent emails are sent without tokens and are subject to existing spam filters.

It’s possible for spammers to send lots of unsolicited contact requests, however separating things out into a spam-free inbox and a “this new person wants permission to email you” queue makes it far more manageable than the current ocean of potential spam in an overflowing inbox. Determining “is this new contact legitimate?” a handful of times is much easier than determining “is this email legitimate?” thousands of times more often.

What you’re essentially doing with this is bootstrapping a social graph on top of email. You can then add a bunch of other nice things on top of that, like public key cryptography, but the actual diff between current email and this system is surprisingly thin.

[0] https://www.biscuitsec.org

snvzz 9 hours ago [-]
There's DIME[0]. I wish I heard about the effort more often, as it's sorely needed.

0. https://en.wikipedia.org/wiki/Dark_Mail_Alliance

riffic 14 hours ago [-]
there shouldn't be a rush to replace the things that have stood the test of time. Lindy's law would suggest a protocol that's been around 40+ years is fundamental and won't be going anywhere anytime soon.
snvzz 9 hours ago [-]
When it comes to SMTP for email, time has only served to highlight its inadequacy.

DMAC, DKIM, SPF, S/MIME, PGP are all ugly workarounds. The issues are fundamental.