# Schemity

> Schemity is an offline desktop ERD tool for software engineers on macOS, Windows, and Linux. It is a $129 one-time purchase with no cloud and no subscription: diagrams are plain local JSON files you can version control with Git. Design a schema from scratch or reverse engineer a live PostgreSQL, Supabase, MySQL, MariaDB, SQL Server, or SQLite database, break large schemas into focused context views, review generated migration SQL diffs, and get AI help via bring-your-own-key providers or local Ollama models - nothing leaves your machine.

Key terms: a "context view" is a focused, read-only sub-diagram showing a subset of the main ERD, which stays the single source of truth.

## Docs

- [What is Schemity](https://schemity.com/doc/what-is-schemity/): Overview of the offline ERD tool and its core ideas.
- [Quick start](https://schemity.com/doc/quick-start/): From install to first diagram.
- [Reverse engineer a database](https://schemity.com/doc/reverse-engineer-database/): Turn a live database schema into an ERD.
- [Re-sync with the live database](https://schemity.com/doc/resync-database/): Keep a reverse-engineered ERD current while preserving layout.
- [Context views](https://schemity.com/doc/context-views/): Focused sub-diagrams from one source of truth.
- [Relationships](https://schemity.com/doc/relationships/): Crow's foot notation, 1:1 vs 1:N vs N:N, referential actions.
- [Check constraints and composite unique](https://schemity.com/doc/check-constraints-composite-unique/): Business rules and multi-column uniqueness in the diagram.
- [Migration SQL diff](https://schemity.com/doc/migration-sql-diff/): Review generated SQL before anything touches the database.
- [JSON storage format](https://schemity.com/doc/json-storage-format/): Diagrams as plain local JSON files.
- [Version control with Git](https://schemity.com/doc/version-control-git/): Diagrams reviewed in pull requests.
- [AI-assisted design](https://schemity.com/doc/ai-assisted-design/): BYOK chat that edits the diagram, including local Ollama models.

## Comparisons

- [Schemity vs ChartDB](https://schemity.com/blog/schemity-vs-chartdb/): The offline desktop alternative to ChartDB.
- [Schemity vs dbdiagram.io](https://schemity.com/blog/schemity-vs-dbdiagram-io/): The offline alternative to dbdiagram.io.
- [Schemity vs DbSchema](https://schemity.com/blog/schemity-vs-dbschema/): The lightweight one-time-purchase alternative.

## Guides

- [Crow's foot notation explained](https://schemity.com/blog/you-have-been-reading-erd-notation-wrong/): Every ERD notation symbol mapped to SQL constraints.
- [Design a multi-tenant RBAC data model](https://schemity.com/blog/design-data-model-for-multi-tenant-rbac/): Walkthrough from use cases to schema.
- [Design first, ship by context](https://schemity.com/blog/design-first-ship-by-context/): One ERD from sketch to production.
- [Blog index](https://schemity.com/blog): All posts on database design, ERD workflows, and schema documentation.

## Product

- [Pricing](https://schemity.com/pricing/): $129 one-time purchase, free forever for education.
- [FAQ](https://schemity.com/faq/): Common questions about the desktop ERD tool.
- [Schemity Lite](https://schemity.com/lite/): Free browser-based schema designer for quick sketches.