This page is for the current stable release of Schemars (v0.8.x).

To view this page for the v1 version of Schemars, which is still under development, click here.

Deriving JsonSchema

This is the simplest usage of Schemars. Both types are made to derive JsonSchema, and the schema_for! macro is used to generate the schema itself.

use schemars::{schema_for, JsonSchema};

#[derive(JsonSchema)]
pub struct MyStruct {
    pub my_int: i32,
    pub my_bool: bool,
    pub my_nullable_enum: Option<MyEnum>,
}

#[derive(JsonSchema)]
pub enum MyEnum {
    StringNewType(String),
    StructVariant { floats: Vec<f32> },
}

fn main() {
    let schema = schema_for!(MyStruct);
    println!("{}", serde_json::to_string_pretty(&schema).unwrap());
}

Click to see the output JSON schema...

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "MyStruct",
  "type": "object",
  "properties": {
    "my_bool": {
      "type": "boolean"
    },
    "my_int": {
      "type": "integer",
      "format": "int32"
    },
    "my_nullable_enum": {
      "anyOf": [
        {
          "$ref": "#/$defs/MyEnum"
        },
        {
          "type": "null"
        }
      ]
    }
  },
  "required": [
    "my_int",
    "my_bool"
  ],
  "$defs": {
    "MyEnum": {
      "oneOf": [
        {
          "type": "object",
          "properties": {
            "StringNewType": {
              "type": "string"
            }
          },
          "additionalProperties": false,
          "required": [
            "StringNewType"
          ]
        },
        {
          "type": "object",
          "properties": {
            "StructVariant": {
              "type": "object",
              "properties": {
                "floats": {
                  "type": "array",
                  "items": {
                    "type": "number",
                    "format": "float"
                  }
                }
              },
              "required": [
                "floats"
              ]
            }
          },
          "additionalProperties": false,
          "required": [
            "StructVariant"
          ]
        }
      ]
    }
  }
}