# SCAN: the open notation

**SCAN (System and Component Architecture Notation) is an open, human-readable notation for describing software systems.** Sphere is built on it. SCAN itself is free and open.

SCAN is the **Architecture-as-Code** substrate: the blueprint language for the living system model. Sphere turns that blueprint into plans, builds, verification, and memory. Without a shared notation, agents and people rebuild context from prose and file dumps every session.

## What SCAN describes

- **Components:** services, apps, data stores, agents, external systems.
- **Connections:** what talks to what, and how.
- **Ports and interfaces:** where components connect.
- **Technology:** what each component is built with.
- **Boundaries:** groupings such as domains, teams or deployment zones.
- **Layout and views:** how the model is drawn on a board.

A SCAN model is plain text (YAML), so it can live in a repository, be reviewed like code, and be read by both people and AI agents — the same ground truth for BA, Dev, Architect, QA, and coding agents.

## Why an open notation matters

- No lock-in for your architecture — the model is yours, in an open format.
- Toolable — anyone can read, render or generate SCAN.
- Shared language for people and AI agents.
- Structured context that is far more useful to agents than prose alone or a pile of source files.
- Context that **persists** across changes instead of being rebuilt each time.

## SCAN vs Sphere

| | SCAN (free, open) | Sphere Desktop (product) |
|---|---|---|
| Notation and specification | Yes | Yes |
| Browser whiteboard at app.spherescan.io | Yes (diagram canvas) | — |
| Chat-first architect / orchestrator | — | Yes |
| Plans, runs, builds, verification | — | Yes |
| Private workspace with a live, reconciled model | — | Yes |
| Persistent memory of plans, runs and verification | — | Yes |
| Collaboration, governance, connected systems | — | Yes |

**app.spherescan.io** is the free SCAN whiteboard — useful for trying the notation, not a substitute for Sphere Desktop. For how Desktop works (Chat, Plans, Runs, Diagram), see `sphere-desktop.md`. Learn more at https://spherescan.io.