Architecture overview
Four layers, read top to bottom: the assistants you already use, the protocol they speak, the program that runs on your computer, and the four storage tiers your vault spans. Three of those tiers are free because they're your own hardware; only the fourth, the shared server, costs anything.
You
Ask a question, or say "remember this"
Plain conversation, in the app you already use.
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Your assistant
Passes the request on
Claude, Cursor or anything else that supports MCP. Five requests, nothing more.
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ModelBrain
Searches your vault and answers
Runs on your machine. Returns a handful of notes with dates and sources attached.
Optional · folder sync
Point it at a folder of your own documents
Word, PDF, Markdown and plain text. You approve the folder at the keyboard, once — an assistant can never add one for you.
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It reads them into your vault and keeps up with changes: new files are added, edited files are updated, and a file you delete is removed from memory in full — not a paragraph at a time.
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Result
Your documents become answerable
Nothing is uploaded to do this. Reading and indexing happen on your own computer.
Folder sync is a read of files you choose; it never writes to them. Scanned pages and spreadsheets aren't supported yet.
The four tiers, and why a memory moves between them
A tier is just where a memory physically sits right now. Things you've used lately sit somewhere fast; things you haven't sit somewhere cheap. You never choose a tier, and moving between them changes nothing about what a memory is.
Tier 1free
In memory
Your computer's RAM. What you're working on right now, plus the search indexes.
instant
smallest
rebuilt on restart
Tier 2free
On your disk
Your vault. Everything from the last few months, stored so it can be read without unpacking first.
fast
uncompressed
always available offline
Tier 3free
Compressed on your disk
Older memories you rarely ask about, squeezed down so a long history doesn't fill your drive.
slightly slower
much smaller
still offline · still yours
Tier 4paid · opt-in
On a server
Only if you switch it on: a copy your other device or your team can reach. Never happens by default.
needs a connection
shared, not private
designed, not built
Used often · fast · on your machine
Rarely used · cheap · optionally elsewhere
What never changes when a memory moves
What it says, when you saved it, and where it came from.
Whether it's deleted. Moving a memory to a cheaper tier is not forgetting it, and a deleted memory stays deleted wherever it sits.
Its version history, so a correction is still a correction after the move.
Whether your assistant can recall it — every tier is searchable. A tier affects speed and space, never answers.
What decides where something sits
How recently it was used. That's the whole rule in the first version — simple enough to check, and it produces the data that would justify anything cleverer.
Anything private is removed from what's even eligible for Tier 4 before placement runs. Privacy is a filter, not a factor weighed against saving space.
Tiers 1–3 are all your own hardware, so nothing leaves your computer as a memory ages. Only turning on Tier 4 changes that.
Claude Desktop
Claude Code
Cursor
any MCP client
rememberrecallforgetexpandconnector_syncover a local socket — nothing administrative is in this vocabulary
Layer 3
ModelBrain, on your computer
One program. One writer. No daemon to babysit, no Python, no separate database.
Write path
Embed, encode, append, flush to disk, update the index.
Read path
Filter, over-fetch by similarity, rescore. Keywords and meaning together.
Embeddings
llama.cpp, in-process, on your CPU. No API call.
Connectors
Reads folders you approved at the keyboard. Markdown, TXT, PDF, DOCX.
Layer 4
Where memories sit
Moving between tiers never changes what a memory means. Eviction is not forgetting.
Tiers 1–2 · free foreverEverything on your own machine. No account, no limit on size.
1 · Memory (RAM)free · in v1
What you're working on now, plus the hot search indexes. Fastest, smallest, not durable on its own.
2 · Regular diskfree · in v1
Your vault. Read directly with no decompression step, which is why it isn't compressed or encrypted here.
Tiers 3–4 · designed, not builtTier 3 stays free — it's still your disk. Tier 4 is the paid, opt-in one, and nothing here claims it works today.
3 · Compressed diskfree · designed
Older memories, still on your machine and still available offline, taking less space. Free, because it's your disk.
4 · Serverpaid · designed
The only tier that costs money: a shared collection for your own second device or a team. Anything private is excluded before a block is even eligible to go here.
Why one program instead of a stack
Search, storage and embeddings are in the same binary, so there's nothing to install alongside it and nothing that can be up while something else is down. It also means the whole thing runs with no network access at all.
Why one writer
Exactly one part of the program is allowed to change your vault. Housekeeping and tier movement publish their work through it rather than writing in parallel, which is how deletions stay deleted across a restart.
Known gaps at this layer
Multi-step writes need a defined unit of atomicity, and the housekeeping process needs its publication serialised through the single writer. Both are open engineering items, tracked in the changelog rather than glossed over here.