A while ago, I shared my journey of building Second Brain Joiner—a local-first iOS app designed to safely merge Obsidian markdown vaults and feed them into LLMs like ChatGPT and Claude without relying on cloud servers or risking privacy.
The response from the community was amazing. But the number one request I received was loud and clear: "When is the Android version coming?"
I hear you. As an indie developer and a massive Obsidian fan myself, I knew I had to make it happen. Today, I’m incredibly excited to announce that Second Brain Joiner is officially live on Google Play! 🎉
👇 [Get it on Google Play]
🎥 [Watch the Quick Demo]
🚀 Building the Android Version:
Not Just a Port, an Evolution
When I started building the Android version, I didn't want to just port the iOS app as-is. As I used the app daily for my own workflow, I realized that power users need more granular control over what they send to the AI.
Throwing your entire vault at an LLM is a bad idea (hello, context window limits and hallucination!). You need precise context.
So, I built the Android version from the ground up with a completely new set of "Pro" features tailored for heavy AI users:
1. OpenAI API-Based Token Calculation
Word counts are useless for AI. You need to know the exact token count. I implemented a highly accurate token calculation system based on the OpenAI API standard, so you know exactly how heavy your prompt is before you paste it.
2. Advanced Filtering (AND/OR Logic)
You can now pinpoint exactly which notes to merge. The app allows you to combine Tags and Last Modified Dates (From-To) using flexible AND/OR conditions. Want to extract only notes tagged with #project-x that were updated in the last 7 days? Now you can do it in seconds.
3. Auto Chunking for Large Vaults
If your merged text exceeds practical LLM limits, the app now features an Auto Chunking system. It intelligently splits your massive markdown outputs into manageable chunks so you can feed them to ChatGPT or Claude sequentially without breaking the context window.
🍎 What about iOS users? (The Backport Promise)
If you are currently using the iOS version, you might be thinking, "Hey, what about us?" Don't worry! I haven't forgotten you. Developing these advanced features on Android first allowed me to refine the logic and UI. I am officially announcing that all of these new features (Advanced Filtering, Auto Chunking, and Token Calculation) will be backported to the iOS version in an upcoming major update. Stay tuned!
💡 Fully Local, Fully Secure
Just like the iOS version, the Android app respects your privacy. It processes your .md files entirely locally on your device. No servers, no data harvesting, no sneaky API calls in the background. Your second brain stays yours.
If you are an Android user looking to supercharge your Obsidian + AI workflow, I would love for you to give it a try and let me know what you think!
Happy Linking! 🧠✨
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