Commonplace
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A notebook that keeps its own index.

Commonplace gives every note a permanent number, links it to what you wrote before, and builds an index at the back, the way a good book has one. A second brain you can find your way back into.

Start freeSee how the index works
Entries
Unlimited, numbered for good
Stored as
Plain text, on your device
Runs on
Mac, Windows, phones, web
Costs
Free to 1,000 entries
Entry 214.3 open in Commonplace, with recent entries on the left and its links and a resurfaced note from March 2024 in the margin.
Reading and research2,611 entries

Entry 214.3, branched from 214, written 12 September 2026

The forgetting curve is a filing problem

Ebbinghaus tested himself on lists of nonsense syllables in the 1880s and watched most of each list disappear within a day. What brought a list back was meeting it again, at intervals, before it had gone completely.

So a notebook that only stores things works against memory. The useful ones put an old note in front of you at the moment you need it, which is what filing was always for. See 41.2 Spaced repetition and 12.4 Attention residue.

Indexed under Ebbinghaus, forgetting, memory, timing

How Commonplace files a thought

Five habits that people kept by hand in commonplace books for centuries. The software keeps them for you, so writing is the only job left.

  1. Capture

    Write wherever the thought arrives: the desktop app, your phone, the share sheet, or an email to your notebook's own address. Each note is saved as an entry and given the next free number.

    Menu bar, share sheet, email, reading highlights

  2. Branching

    Reply to an entry to continue the thought beneath it. A reply to 214 becomes 214.1, and a reply to that becomes 214.1a, so a line of thinking stays in order without a single folder.

    214, then 214.1, then 214.1a

  3. Linking

    Type two square brackets and a few words to cite another entry. Both entries show the link, so an old note learns what was written after it.

    Type [[ spaced to find 41.2 Spaced repetition

  4. Recall

    While you write, earlier entries that share your words wait in the margin. Nothing pops up or interrupts; you look across when you want to.

    Matched on your own words, on your own device

  5. The index

    Every term you come back to gets a line at the back of the notebook, with the number of each entry that uses it. It updates as you write.

    People, books, places and ideas, A to Z

An index at the back, built as you write.

When you can’t remember where you put something, open the index the way you would in a book. You will usually find the note you wanted, and two more you had forgotten you wrote.

Part of one reader’s index: terms in alphabetical order, each followed by the numbers of the entries that use it.
  • Aristotle, on habit 7.3, 7.3a
  • Attention, residue of 12.4, 88.1
  • Attics, digital 219.1
  • Bayes, slow updating 41.2, 190.4
  • Bees, the waggle dance 133.1
  • Books, unread 26.1, 26.2

A few of 1,284 terms, drawn from 2,611 entries. The rest of this index runs on through Z.

Keeping a commonplace book is an old habit. The filing was always the hard part.

  1. 1706

    John Locke's method for indexing a commonplace book appears in English: one spread at the front, a grid of first letters and vowels, pointing to every page that follows.

  2. 1951

    Niklas Luhmann starts the slip box he will keep for over forty years. About 90,000 cards, each with a branching number, so a new thought could grow in the middle of an old one.

  3. 2026

    Commonplace keeps both habits and does the filing: the numbers, the links and an index that stays current on every device you own.

Yours, in plain text

A second brain is only worth building if it outlasts the app you built it in.

Storage
Every entry is a Markdown file in a folder you choose, on your own device.
Sync
Encrypted end to end between your devices. Our servers hold ciphertext and cannot read a word of it.
Export
One click exports everything, including the index as a plain text file.
Offline
Every feature works without a connection. Sync catches up when you are back.
Suggestions
Links and resurfaced entries are worked out on your device. Your writing never trains anyone's model.
If we close
Your notebook is already a folder of text files on your disk, readable in any editor for as long as you keep it.

Pricing

Every plan has every feature. You pay for room and for sync, and you can leave with everything at any point.

  • Notebook

    $0

    Free, for as long as you like

    Your first 1,000 entries, on one device and the web.

    • Numbering, links, recall and the index
    • Import from Markdown and plain text
    • Export whenever you want
    Start free

  • Personal

    $6

    A month, billed yearly at $72

    Unlimited entries, on every device you own.

    • Encrypted sync across devices
    • The full history of every entry
    • Your reading highlights, imported
    Start a 30-day trial

  • Lab

    $10

    Per person, a month

    One shared index for a research group, a newsroom or a small team.

    • Shared and private entries side by side
    • One index across the whole group
    • Admin controls and single sign-on
    Start a lab trial

Questions

Do I have to number my notes myself?

No. Every entry gets its number the moment you save it. To place a thought under another one, reply to it, and the new entry takes that number as its prefix.

Can I bring the notes I already have?

Yes. Point Commonplace at a folder of Markdown or plain text files. Each file becomes an entry, the links between them are kept, and the index is built on the first run.

What happens to my notes if Commonplace shuts down?

Nothing. They already live on your disk as text files, and the app only reads and writes them. The export includes the index, so even the filing survives.

Is my writing used to train AI models?

No. Sync is encrypted end to end, so we cannot read your entries, and the suggestions in the margin are worked out on your own device.

Does it work without an internet connection?

Completely. Write, link and search offline; your other devices catch up the next time they connect.

Start with one entry.

Write down what you are thinking about right now. Commonplace will give it a number and remember where it is.

Free for your first 1,000 entries. No card, no folders to set up.