Both speak ActivityPub and yes you can use a Mastodon client to interact with Lemmy communities.
I did a bunch of experiments today and ... thoroughly confused myself.
Here's what I learned:
(I have more protocol info but ultimately this is the lived experience of working across different software systems, federation, and the actual client / front end web experiences that people interact through)
Various things "just work" by pasting URLs into the Mastodon web interface or the Mastodon mobile app.
Posting the link to this post https://lemmy.ca/post/606549 finds this post
Clicking on the user profile shows me a profile for [email protected], with one post displayed. Including a follow button
Only one post is shown, because that's all that's available on the local server right now. If I chose to follow Doctor_Pi's Lemmy account, I'd get all of their posts going forward. Both OPs (which has a link to the post on Lemmy.ca) as well as comments (which appear as replies).
Other clients (Ivory on iOS) have extremely variable support. You can't usually paste in Lemmy URLs, but you can paste in Lemmy accounts and follow them, and then see posts going forward.
You can't create an "original post" using just a Mastodon account, you have to have a Lemmy account and create it somewhere (I'd love this to be not true, and maybe we can make this a feature request!)
Every Lemmy user can be followed on Mastodon. So, for example, my Lemmy account @[email protected]. Paste that into the web interface of Mastodon or into the Mastodon native mobile app and you will find my Lemmy profile and can follow it.
If you reply to a Lemmy post using your Mastodon account, your reply will be posted as a comment. A user profile is created on the Lemmy instance.
I just did that with this very post, and it seems to have worked.
This is my [email protected] Mastodon account, viewed through news.cosocial.ca as a local user profile. All of that info -- including the images -- are from my Mastodon profile.
The comment is technically originally on Lemmy.ca.
I'll leave it there for now. Still exploring different combinations. I have two questions / features I'd like to enable for Lemmy <> Mastodon.
- ~~Being able to create OP directly from Mastodon~~ works!
- You'd be limited by character limits, lack of more formatting, no inline images, and so on. Depending on your Mastodon server you might have larger character limits, or something like the Elk or Phanpy web front ends could enable "Lemmy mode" from your Mastodon account.
- If I were designing this, I'd do it as maybe a DM to the group account. e.g. DM
@[email protected].
This does work, see @smorks, and his post on Mastodon.
- Logging in to a Lemmy instance with your Mastodon account
- If it's already creating profiles for Mastodon accounts, why not go all the way and just use your Mastodon account to login? You need to trust your Mastodon host more than your Lemmy host.
- More likely: a "linking" mode, where you do need a "local" account, but you can link it with your Mastodon account so there aren't two of you :)