As a systems engineer and a long-time Obsidian user, I’ve always wanted a seamless way to feed my entire “Second Brain” into AI models like Gemini or Claude. I looked for existing tools that could handle batch-processing my notes (both from free and paid apps) into a clean, single format, but I couldn’t find exactly what I needed.
So, I decided to build it myself.
It’s called “Second Brain Joiner”. I originally designed this for my own workflow, but it worked so well that I wanted to share it with this amazing community.
What it does: It’s a lightweight Google Cloud Function that merges your vault (ZIP) into a single, AI-ready Markdown file. It ensures privacy (runs on your own cloud) and even handles things like Japanese filename encoding and integrity reporting.
Why I’m sharing this: I’ve made the source code completely Open Source on GitHub. I believe in the power of shared knowledge, so please feel free to use it, tweak it, or take it apart!
If this tool saves you even five minutes of tedious work, or helps you gain new insights from your notes, it would make me incredibly happy.
Thanks for the assist with the link, Marko! As a newcomer, I’m still navigating the trust levels here. Glad to meet someone who shares the vision of bridging Obsidian and AI. Cheers!
To make things even clearer, I’ve put together a simple diagram of the workflow. Hope this helps anyone looking to bridge their Obsidian vault with AI!
To make the setup process smoother for everyone, I’ve completely revised the README.
Visual Aids: Added 10+ screenshots of the Google Cloud Console.
Detailed Steps: Refined the instructions based on feedback to be more granular and beginner-friendly.
I haven’t changed the core logic this time, but this “manual update” should help everyone get started without the headache.
Check out the new guide here:
[https://github.com/Hirofumi-I/second-brain-joiner.git]
Some of you might remember my post from January about the Google Cloud Function I built to merge vault files. Since then, I’ve been using it every day, but as my own vault grew to over 1.7MB, I realized I needed something faster and more “architected” for AI. So, I decided to build a native iOS app myself.
It’s still called Second Brain Joiner, but it’s much more powerful now. What’s new in this version:
Native & Local: No more ZIP uploads or cloud functions. It runs entirely on your iPhone/iPad.
Tree Map: It automatically generates a directory structure at the top, so the AI understands your knowledge hierarchy.
Smart Separators: I’ve implemented explicit [DOCUMENT START] and [DOCUMENT END] tags to keep notes distinct for the AI.
Property Preservation: It keeps all your YAML metadata intact—essential for deep AI reasoning.
I also developed VaultPress. To be honest, I struggled to find any app—free or paid—that correctly handled Obsidian-specific Markdown for PDF export on iOS. So I made it myself. It supports Obsidian’s unique formatting and internal links, allowing you to print or share your notes exactly as they appear in your vault. It’s the tool I needed to finally “take my notes out” of Obsidian.
I just wanted tools that worked perfectly for my daily workflow without compromising privacy. Since I built these to solve my own daily frustrations, I’ve made them available as a one-time purchase (no subscriptions!).
You can check them out individually, or grab the discounted bundle if you want to complete your mobile workflow for both AI input and flawless PDF output. Feel free to take a look and see how it works for your own vault!
P.S. I also just launched this bundle on Product Hunt today! If you like what I’ve built or find it useful, I’d be incredibly grateful for your support and feedback there:
after a loooong wait in Apple’s App Review process, Ultimate Second Brain Kit App - App Store is finally officially approved and live on the App Store!
For those who want to complete their mobile workflow (both the AI connector and the beautiful PDF exporter) at a discounted price, the bundle is now available.
I also put together a super short (55 sec) demo video showing just how fast it works. You can see it instantly merge hundreds of my vault notes and feed them directly into Gemini for deep context understanding, all fully locally on iOS.
A huge thank you to everyone who has already checked out the individual apps (I even got my first organic sale from Latin America, which absolutely blew my mind as an indie developer!).
If you have any questions or feature requests, please let me know. I’m actively working on improving the apps based on your feedback (and yes, I’m currently working hard on the Android version too!).
In my last post, I mentioned that I was working hard on the Android version… and today, I’m thrilled to announce that Second Brain Joiner is officially live on Google Play!
Instead of just porting it, I rebuilt it from the ground up for Android with some massive “Pro” upgrades tailored for heavy AI users:
Precise Token Calculation (OpenAI API standard)
Advanced Filtering (Combine Tags/Dates with AND/OR logic)
Auto Chunking (For massive vaults)
Here is a quick demo of how it works:
Get it on Google Play:
I also wrote a dev story on Dev.to about why I built these features and my commitment to local-first privacy. If you are interested, you can read it here:
(And yes, I promise to backport these new features to the iOS version soon! )
Thank you all for reading, and Happy Linking!
In my last post, I promised to bring the massive “Pro” upgrades from our Android launch over to iOS. I know many of you iOS users have been waiting patiently, and today, I’m thrilled to announce that the backport is completely finished. Second Brain Joiner for iOS has just received its biggest update yet.
Your iOS app now fully supports the exact same advanced capabilities:
Precise Token Calculation (OpenAI API standard)
Advanced Filtering (Combine Tags/Dates with AND/OR logic)
Auto Chunking (Seamlessly handle massive vaults)
The “7-Day Free Trial” Philosophy (Android update) I also have an important update for our Android users. I’ve officially introduced a 7-Day Free Trial on Google Play.
I built SBJ as a precision tool to bridge the gap between my own local vault and LLMs. Because I strongly believe in a “pay once, own it” philosophy over endless subscriptions, I want you to have the exact same confidence. I want you to use it freely for a week, throw your heaviest vaults at it, and decide with your own eyes if this tool is worth investing in for your personal productivity ecosystem.
Whether you are on iOS or Android, thank you all for the incredible support, feedback, and for being part of this local-first journey.
Here is a quick demo of how it works:
Get it on Google Play:
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I also have an important update for our Android users. I’ve officially introduced a 7-Day Free Trial on Google Play.