Most digital commonplace books die the same way. You start strong, collect 200 passages in your first month, and six months later you cannot remember what is in there or where to look.
Capture is not what kills them. Capture has never been easier. The thing that kills them is the gap between saving a passage and ever reading it again.
A commonplace book without that loop is a hoard. I have run one like that. Twice.
What belongs in it, and what doesn't
Anything you expect to return to on purpose.
A paragraph from an essay that reframed something for you. A sentence you want to steal for your own writing. A stanza from a song (lyrics count, the best commonplace books always have them). An observation you had walking to your car. A quote from a book that shifted something.
Before you save something picture yourself reading it again in six months. If that does not feel like a good use of your time, it does not belong in your book. Articles you have not read go in a read-later queue. Tabs you are scared to close go in that queue or the trash. Tasks go in a task manager. Links that seemed cool once go nowhere.
A commonplace book is narrower than all of those. That narrowness is kinda the point. A hundred passages you actually love beats ten thousand you will never open again.
Organization that survives past 500 entries
In 1706 John Locke (no, not the guy from Lost) published A New Method of a Common-Place-Book. It was mostly a system for page indexing. Categories across the top of each page, an index at the front, a rule for which topics lived where. The point was to stop the book becoming a pile.
Modern tools give you infinite pages. That makes the same problem worse, not easier.
What works:
- A small set of durable topics you keep returning to. Not forty. Closer to eight.
- Every entry tagged with one topic, maybe two. Rarely more.
- One top-level index or dashboard that lists your topics with a count. You want to glance and know what you have a lot of.
- Search as a fallback, not the plan.
Nested folders three levels deep do not work. Neither does a tag for every interesting noun. Treating search as organization does not work either. You build a maze only today-you can navigate, and then six months later you need a passage you know you saved and cannot find.
How Notion, Obsidian, Apple Notes, Readwise, and Keep stack up for this
Five common setups. Each has a sharp edge and a real cost.
Notion. Structurally the most templated. You can build a beautiful commonplace book page with properties, relations, and views. Capture is slower than every other option on this list. Your content lives inside Notion and is annoying to get out. If you already live in Notion, the friction is lower.
Obsidian. The most organizationally powerful. Backlinks and graph view make it the only tool here where entries talk to each other. The cost is learning curve and vault discipline. Without a clear structure Obsidian vaults sprawl faster than Notion workspaces. If you are willing to invest, nothing beats it for reading what you have written.
Apple Notes. The fastest capture on the list by a wide margin. Type, shake, done. Organization is the weakest here. Search is serviceable. Programmatic access is essentially nil. Fine for small books, brittle at scale.
Readwise Reader. The best option if your commonplace book is mostly highlights from articles, books, and PDFs you are reading anyway. Daily review is built in. It costs around ten dollars a month, and it wants to be the place you read, not only the place your highlights live. If your sources are scattered across X, YouTube, newsletters, and PDFs, routing everything through Reader is a big ask.
Keep. Capture from anywhere (extension, iOS share sheet, email, X sync). Every entry is stored as clean markdown by default. No graph, no bidirectional links, no review-queue UI, and no in-article highlighting yet (so you save the whole source and pull passages back with search or an LLM query against the full text). Obsidian wins if your commonplace book needs a knowledge graph. Readwise wins if you want passage-level highlights with a daily review built in. Keep wins if you want every source you save sitting in one portable, LLM-readable library.
Readwise and Obsidian are the two tools to beat for a digital commonplace book right now. Keep is sharpest when you save a lot from many places and plan to query it back out with search or an LLM. Notion and Apple Notes are easier starting points if you want to begin today.
What a commonplace book entry looks like when saved as markdown
Paste any article URL below and watch it turn into the kind of source entry you might save. Title, body, source link, nothing else. This is what the extraction pipeline behind Keep returns for every URL it ingests.
Plain text you can read, search, diff, and hand to an LLM without any conversion step.
That entry is the whole article. If you want only the excerpt (the one paragraph or sentence you actually care about) you need a tool that supports in-article highlighting, and Keep doesn't have that yet. So Keep belongs to the source-first flavor of commonplacing. You save the whole thing and find your passages back later via search or a prompt against the full text. Readwise and highlight-heavy Obsidian setups do the passage-first flavor. Both are legitimate.
Building a resurfacing loop (the half nobody writes about)
Capture is half. The loop is the other half, and the part almost nobody writes about.
Manual resurfacing with nothing but a calendar
A weekly review of the last seven days works. Fifteen minutes, no tools, just scroll and reread. A monthly re-read of one topic works too. Pick the topic, read every entry tagged with it, move on. A daily random pull is the lightest of the three. Open the book, read whatever appears, close it.
Any of these beats the alternative, which is nothing.
Querying your commonplace book with Claude, Cursor, or any MCP client
Keep stores every save as clean markdown, and it ships a CLI, an MCP server, an agent skill, and an HTTP API. Your commonplace book becomes a dataset any LLM can read. That means you can run actual prompts against it. "Pull three passages I have saved about attention that would fit in a draft about deep work." "Summarize everything I have tagged with writing from the last six months." "Find that quote I saved from the Paul Graham essay about makers and managers."
Claude Code, Cursor, and any MCP-compatible client can read your Keep library today. That is the point where a commonplace book stops being an archive and starts being a working tool.
Obsidian and Notion can do versions of this with effort and plugins. Keep gives it to you by default, because markdown is the native format, not an export.
Locke, Marcus Aurelius, and Ryan Holiday all kept one
None of this is new. Locke published his system in 1706. Marcus Aurelius wrote the Meditations this way, a private commonplace book that happened to become a philosophy. Ryan Holiday runs an index-card version today and has written openly about the method.
The tool keeps changing. Paper, scroll, index card, database, markdown file. What you are doing stays the same. Capture passages worth rereading, build a way to find them again, and come back to them.