Datanotes is the open-source database engine for Markdown: it runs a folder of notes as typed, validated tables that your programs and AI agents query, write and undo over MCP or HTTP, while every row stays a plain file you own.
The engine of your second brain: Markdown notes as database tables, for you and your agents.
Agents can't write garbage. Every write is checked against its table: types, links, unique values and CHECK constraints. A refused write changes nothing. Its answer says which value broke which rule and how to fix it.
Every change can be undone. The engine journals every write it makes. It records who made it: the agent, its session and its token. undo_migration takes any change back.
It's still just Markdown. A row is a note, or a section of a pack note, and its front matter keys are the columns. Read it, edit it, grep it or commit it to Git. The engine reads your hand edits and checks them too.
Extensions. Install tables and MCP tools from a git repository, pinned and confirmed (datanotes extension install).
Local first. Datanotes is Apache-2.0 and runs on your machine. Nothing leaves it unless you turn that feature on.
When not to use it
Datanotes keeps every row as a file, so it isn't a replacement for SQLite or Postgres. Choose a classic database for:
Large analytical datasets
High write throughput
Many concurrent writers on one folder
Datanotes is comfortable at 10,000 notes. At 50,000 notes, the engine takes about 15 seconds for its first start, and 2 to 3 seconds to restart.
Quick start
You need Node.js 22 or newer. On Windows, use Node.js 24.16 or newer, or 26.1 or newer.
Start the engine on a folder, which becomes your database. It can be empty, or hold notes already:
Agents reach the engine through its Model Context Protocol (MCP) server, datanotes mcp. It uses the engine that runs on the folder, or starts one. Every client runs the same command: