I don't think all of it, but parts are. Look at https://github.com/Kimtaro and https://github.com/Jisho-org and you can find some frameworks which are probably used, like "ve". You can also find the actual database for the notes feature (not linked as a data source in the footer), if you're interested in contributing to that.
Yep, like @jakobd2 said, parts of Jisho are open source. Currently https://github.com/kimtaro/ve/ (the linguistics framework that drives a lot of the smarts on the site) and https://github.com/Jisho-org/jisho-notes (data for the sidebar Notes feature) have been open sourced. I plan on releasing more parts as they get cleaned up and generalised to they can benefit others.
That's good to know that you plan to release the source code. Like Eric S. Raymond says, release early, release often ;) you can clean it up over time.
At this time I have no plan on releasing the entire source code. I'd rather concentrate on smaller bits that can be useful to others, like the parts that have already been open sourced.
@Kimtaro - I notice you use Freeling. I was surprised to see you used this, I thought it was supposed to be quite outdated? I'm glad to see that Jisho uses Freeling actually because I am starting a C++ project soon for which I need an English lemmatizer, and Freeling is really one of the only libraries out there that I can use for it. Why don't you use a more up to date library such as nltk, SpaCy, etc?
@MrZen Jisho actually doesn't use the Freeling part of Ve. I implemented that as a proof of concept but never ended up using it.
As for why I chose Freeling, it was implemented ten years ago, so either I wasn't aware of nltk and SpaCy or they didn't exist. If I were to need English parsing today I would definitely look into them as well.
At the time Freeling was a little quirky to set up, but once it was running I had a good experience with it.
Is jisho open source?
If so where can i find the software?