Azimutt is a database exploration and documentation tool made for large databases. Try Azimutt now
PostgreSQL
The world's most advanced open source relational database. Use the DDL SQL dialect of PostgreSQL to design your database schema and convert it to the other ones.
JSON
Not properly a database schema dialect but using the Azimutt JSON Schema structure, you will be able to define your database structure in JSON and convert it to other dialects.
The JSON format is defined here,
you can suggest improvements.