Developer ships Cohestry, a local-first 'second brain' for agent context
A developer posting on r/OpenAI says they prototyped a notes app in GPT Work on their phone while on a trail walk, then iterated for about a month into Cohestry, now released for both iOS and Mac. The app is described as a local-first "second brain" that automatically tags, links and organizes notes, with an MCP bridge on Mac that lets agents pull only the context they need instead of bloating their context window. The author says Apple approved the iOS version on the first submission and that the Mac app is out too, though these are self-reported claims.
According to the author, Cohestry is built entirely on Apple APIs and keeps notes on-device, passing them to agents only through the Mac MCP bridge — one developer's attempt to solve agent context bloat by fetching context on demand.
While taking a walk last month I got fed up by how disorganized the notes I was getting from my agents were getting, I conceived of a second brain that could seed agents context and also automatically tag, connect and organize the notes. I opened GPT Work on my phone and prototyped the first version right there on the trail. I got home and opened it in Xcode and to my amazement it compiled on first try and all the core features worked. I then spent the next month iterating on it until it actually felt right for my own use cases.
That meant importing my own mess of notes and seeing whether the system could make sense of them. It started connecting old ideas to newer work, resurfaced the original note where I had planned a digital legacy app that preserves your memories and personality for loved ones, and linked it to features I had built months later. It also brought back an old life simulation game idea I had completely forgotten about.
By then it had become Cohestry, a native iOS and Mac second brain with a bridge that lets agents pull only the context they need without bloating their context window. My favorite feature is a 3d brain that allows you bounce between the nodes that connect your notes. The mac app allows you import your Apple notes and iCloud syncs it on your phone. Cohestry is local first and fully built on apple API, we never see your notes. They never leave your device except to your agents if your use the MCP on mac. submitted it once it finally felt right, and Apple approved the iOS version on the first try. Mac is out too, would be happy to hear if this brings some ease to your workflow.
https://apps.apple.com/us/app/cohestry-second-brain/id6811573132
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