Skip to content

json_schema.md

Latest commit

 

History

History
48 lines (28 loc) · 1.7 KB

json_schema.md

File metadata and controls

48 lines (28 loc) · 1.7 KB

JSON Schema

flatc can generate JSON Schema for a FlatBuffers schema, and it can also import that JSON Schema back into FlatBuffers' schema IR.

Generate JSON Schema

Generate *.schema.json from *.fbs:

flatc --jsonschema -o out_dir schema.fbs

This produces out_dir/schema.schema.json.

Import JSON Schema

You can use a *.schema.json file anywhere flatc expects a schema file:

flatc --cpp -o out_dir schema.schema.json

This is primarily intended for round-tripping FlatBuffers schemas through JSON Schema tooling, and for downstream workflows that treat JSON Schema as the schema “source of truth”.

x-flatbuffers metadata (optional)

JSON Schema cannot represent all FlatBuffers schema semantics (for example: struct vs table, exact scalar widths, union type mapping, field ids, and presence rules). To enable lossless round-trips, flatc can emit an optional vendor extension:

flatc --jsonschema --jsonschema-xflatbuffers -o out_dir schema.fbs

This adds x-flatbuffers objects at:

  • The schema root (root_type, file_identifier, file_extension)
  • Each definition (enum/union/table/struct metadata)
  • Each field (exact FlatBuffers type + attributes)

Because x-flatbuffers uses the standard vendor-extension mechanism (x-...), most JSON Schema tools will ignore it and continue to work normally (for example QuickType and similar code generators).

x-flatbuffers meta-schema

The allowed keys/values for the x-flatbuffers objects are described by:

  • docs/source/schemas/x-flatbuffers.schema.json:1

This file is a meta-schema for the x-flatbuffers vendor extension itself (not a replacement for the JSON Schema metaschema).