JohnnyDecimal
title: Johnny.Decimal type: technique created: 2026-05-21 last_updated: 2026-05-21 related: ["radar/techniques/ThreePassPaperReading"] sources: ["https://johnnydecimal.com/20-29-communication/22-blog/22.00.0025-systems-data-knowledge/"] radar_quadrant: Techniques radar_ring: Assess radar_position: inner
A personal information architecture system that organises all files, notes, and references into a strict two-level numeric hierarchy, making any item locatable by its number rather than by navigating a folder tree.
Johnny.Decimal divides everything into at most 10 areas (00–90), each containing at most 10 categories (01–99), each containing numbered items (e.g. 22.05):
10-19 Finance
11 Tax returns
11.01 2023 tax return
11.02 2024 tax return
12 Invoices
20-29 Communication
22 Blog
22.00.0025 Systems, data, and knowledge
The constraint — no more than 10 areas, 10 categories — is intentional. It forces decisions about what matters enough to have a dedicated slot, preventing the unbounded folder sprawl that makes most personal filesystems unsearchable.
The Johnny.Decimal blog distinguishes three layers of personal information:
- Systems — processes and workflows (how things get done)
- Data — files and records (the outputs of work)
- Knowledge — understanding (what you know as a result)
These are separate concerns and should not be stored in the same place. Mixing them — putting process documentation next to the files it produces next to your personal notes — creates retrieval friction. The Johnny.Decimal number gives every item a stable, shareable address that survives folder reorganisations.
Most file systems grow organically: a Downloads folder, a Projects folder, nested subfolders with names that made sense at the time. The result is a tree that only its author can navigate, and only immediately after creating it. Johnny.Decimal imposes an upfront constraint that trades short-term setup cost for long-term findability.
The numeric address is also portable: 22.05 means the same thing in your file system, your note-taking app, your email labels, and your task manager — a single lookup space across tools.
Johnny.Decimal sits in the Assess ring of the Techniques quadrant, at inner position. First studied via the Johnny.Decimal blog post on systems, data, and knowledge (2024-01-09). The scheme is opinionated and requires upfront commitment to a numbering structure, but the underlying insight — that files, processes, and knowledge are distinct and should be organised separately — is sound and applicable to any personal information management setup. Assess gate: apply the numbering scheme to one area of work (e.g. a project or a topic domain) and evaluate retrieval friction after 30 days.
