It would be great to have a developer API. TheBrain doesn't need to go opensource for it. There are great software that benefit from open source extensions, while the core remains closed and paid (Sublime Text for example)

A lot of feature requests (like the recent "Duplicating Brains", which has been requested since TB8) can be easily and quickly handled by the opensource community, without bothering the core devs.

Currently, almost every feature request gets closed with the generic "I've documented this feature request" response.

Please consider this.

PS: I'm not the first one to request this. Here's a loyal customer who has been requesting it since the past 7 years! [1][2] @GerSch: I feel you, man.
Two fellow devs wanting an API in 2007: [3]. The same user requesting it again in 2008 [4].
More [5], and more [6]
Here's another customer, with a bolder request: [7] <- this is also one of the top threads on this forum.
There are tons of features that I would like to develop for my personal use and for the benefit of the community

- Most frequently used topics - The pinning option is great, but is manual and limited. Having a node of Most Frequently used items will provide quick access to topics, and can be updated dynamically by an extension

- To be processed tag - Not everything you add to the brain needs to be stuff you know and understand. I come from the world of Anki (an open source, and extremely flexible Spaced Repetition software), and I have the habit of using software to store unprocessed content as well. I want the brain to be able to support that functionality. You just found a great blog post? Just add it to the brain, it will automatically be marked as unprocessed. Once you read it, you can extract out thoughts and links, and mark the blog post as processed. (This is similar to Anki's and Supermemo's Incremental Reading (IR) feature)

- Recommender System - Being a Machine Learning researcher, I can't help but think of adding ML to TheBrain. One of the features I would like is for TheBrain to be able to recommend new links between thoughts! This is not a novel idea, Facebook uses Machine Learning on social graphs to suggest friends. Such a feature could help you discover new connections between knowledge, and help improve your creativity.

- Spaced Repetition - Wander is good, but does it optimize for preventing forgetting? Spaced Repetition is easy to implement, and provides you with an epsilon-optimal strategy to never forget the stuff you've added in your Brain. Essentially, the wander function can be enhanced to simple wander to the nodes that you're most likely to forget soon.

With a dev api, not only do others start contributing to your project essentially for free, but the core devs benefit since supporting a developer API forces them to clean and refactor their codebase for the better. This helps the software mature extremely quickly.
Yup, an API has been requested for a long time. I think if you search the forum, you'll find that it is planned down the road, but they are working on the v9 release right now. Hopefully after that it will be fleshing out the inbox and then work on an API. This would take care (depending on implementation) of a lot of the automation requests for adding information, I'm not sure about recommenders and such, but I like the idea.
macOS 10.13
TheBrain 9.0.239
I can confirm what Zen mentioned is correct.  I've added your suggestions to our existing API feature request documentation.

Thank you,

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