I’ve updated cross-posting to Mastodon to include up to 500 characters. This is for short posts without a title. Longer blog posts with a title still use the title and link back to your blog.
If values other than 500 become common, we can start asking each Mastodon instance for its limit and use that. But I’d like to see how well the current behavior works before any other tweaks.
Splendid! Thank you, Manton!
Bumping this thread as it seems the right place despite its age: Using some Mastodon instances (as well as other Mastodon-API-compliant servers such as Friendica), post lenghts are >> 500 chars. Would it be easily possible to either adopt micro.blog to support these or make it per-user configurable? I’m okay with the current approach (text+link) for some services, but for posting to the Fediverse, I’d prefer full text in crossposts (and maybe, optionally, the link added to this).
(… any chance to see this happen at some point? Interacting with Friendica as my main channel, this is the only real showstopper from adopting micro.blog as my main tool…)
No progress on this yet. I still think it’s a good idea to ask each Mastodon server what its default post length is and use that. It has been hard to prioritize because very few Mastodon servers have changed from the default 500. I don’t currently have a test account on any server with > 500 to test this with.
I don’t know if it’s possible or even advisable, but I use hear-me.social (a clean, safe instance) that has a 15,000 character limit. That doesn’t really feel like a limit 
I know. Would it possible to add an allowance for instances that have longer post limits? Maybe just on a per request basis. I’d not want you to try to find all of the instances that allow longer posts and what their individual limits are, not would I expect that you’d even consider it. I certainly wouldn’t! 
Is there an API thingamabob that lets you discover that limit? -THX!
I can be your guinea pig