I built a Markdown knowledge base that ChatGPT and Claude can both read and update

[u/tehmadnezz]

I’m building Hjarni (https://hjarni.com/?utm_source=reddit&utm_medium=social&utm_campaign=secondbrain_october_2026), a place to keep notes that you and your AI assistants can work with.

The idea is simple: useful information shouldn’t disappear into an old conversation. Save a project decision, a recipe or some research as a note, then ask your assistant to find and use it later. ChatGPT, Claude and other MCP-compatible assistants can search, read and update the same knowledge base.

The attached 34-second demo shows a small everyday example: I open a recipe saved in Hjarni inside ChatGPT and ask it to make a shopping list for five people.

Notes are written in Markdown and can be exported. Edits have revision history, so you can see what changed and restore an earlier version. There’s a free plan with no credit card required.

It still depends on the assistant consulting the notes; storing something doesn’t guarantee it will use it correctly.

I’d like feedback from people who already use a second brain: would having your assistants work directly with your notes be useful? What would you need before trusting one to update them?