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6.2.0 • Public • Published


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Conversion library for transforming Joi schema objects into Swagger OAS 3.0 schema definitions.

// input
  id:      joi.number().integer().positive().required(),
  name:    joi.string(),
  email:   joi.string().email().required(),
  active:  joi.boolean().default(true),
// output
  "type": "object",
  "required": ["id", "email"],
  "properties": {
    "id": {
      "type": "integer",
      "minimum": 1
    "name": {
      "type": "string"
    "email": {
      "type": "string",
      "format": "email"
    "created": {
      "type": "string",
      "nullable": true,
      "format": "date-time"
    "active": {
      "type": "boolean"
  "additionalProperties": false


const j2s = require('joi-to-swagger');

const { swagger, components } = j2s(mySchema, existingComponents);

- in case of ES6 module syntax:

import j2s from 'joi-to-swagger';

const { swagger, components } = j2s(mySchema, existingComponents);

J2S takes two arguments, the first being the Joi object you wish to convert. The second optional argument is a collection of existing components to reference against for the meta className identifiers (see below).

J2S returns a result object containing swagger and components properties. swagger contains your new schema, components contains any components that were generated while parsing your schema.

Supported Conventions:

  • joi.object()

    • .unknown(false) -> additionalProperties: false
    • .required() on object members produces a "required": [] array
    • .pattern(pattern, JoiSchema) -> additionalProperties: [Schema]
  • joi.array().items() - in case of multiple provided schemas using items() method, the "oneOf" (OAS3) keyword is used

    • .min(4) -> "minItems": 4
    • .max(10) -> "maxItems": 10
    • .unique(truthy) -> "uniqueItems": true
  • joi.number() produces "type": "number" with a format of "float"

    • .precision() -> "format": "double"
    • .integer() -> "type": "integer"
    • .strict().only(1, 2, '3') -> "enum": [1, 2] (note that non-numbers are omitted due to swagger type constraints)
    • .allow(null) -> "nullable": true
    • .min(5) -> "minimum": 5 (joi.ref is supported and will fallback to 0 if not provided via refValues metadata)
    • .max(10) -> "maximum": 10 (joi.ref is supported and will fallback to 0 if not provided via refValues metadata)
    • .positive() -> "minimum": 1
    • .negative() -> "maximum": -1
    • .valid(1, 2) -> "enum": [1, 2]
    • .invalid(1, 2) -> "not": { "enum": [1, 2] }
  • joi.string() produces "type": "string" with no formatting

    • .strict().only('A', 'B', 1) -> "enum": ["A", "B"] (note that non-strings are omitted due to swagger type constraints)
    • .alphanum() -> "pattern": "/^[a-zA-Z0-9]*$/"
    • .alphanum().lowercase()
    • .alphanum().uppercase()
    • .token() -> "pattern": "/^[a-zA-Z0-9_]*$/"
    • .token().lowercase()
    • .token().uppercase()
    • .email() -> "format": "email"
    • .isoDate() -> "format": "date-time"
    • .regex(/foo/) -> "pattern": "/foo/"
    • .allow(null) -> "nullable": true
    • .min(5) -> "minLength": 5
    • .max(10) -> "maxLength": 10
    • .uuid() -> "format": "uuid"
    • .valid('A', 'B') -> "enum": ['A', 'B']
    • .invalid('A', 'B') -> "not": { "enum": ['A', 'B'] }
  • joi.binary() produces "type": "string" with a format of "binary".

    • .encoding('base64') -> "format": "byte"
    • .min(5) -> "minLength": 5
    • .max(10) -> "maxLength": 10
    • .allow(null) -> "nullable": true
  • produces "type": "string" with a format of "date-time".

    • .allow(null) -> "nullable": true
  • joi.alternatives() - structure of alternative schemas is defined by "anyOf", "oneOf" or "allOf (OAS3) keywords

    • .mode('one') -> produces "oneOf": [ { ... } ]
    • in case of joi.required() alternative schema, the custom property option "x-required" is added to subschema -> "x-required": true
  • joi.when() conditions are transformed to "oneOf": [ { ... }, { ... } ] keyword

    • if multiple joi.when().when() conditions are provided, they are transformed to "anyOf": [ { ... }, { ... } ] keyword
    • in case of joi.required() condition, the custom property option "x-required" is added to subschema -> "x-required": true
  • any.default() sets the "default" detail.

  • any.example() sets the "example" or "examples".

    • .example('hi') -> "example": "hi"
    • .example('hi', 'hey') -> "examples": ["hi", "hey"]
  • joi.any()

  • .meta({ swaggerType: 'file' }).description('simpleFile') add a file to the swagger structure

  • .valid(1, 'A') -> "enum": [1, 'A']

  • .invalid(1, 'A') -> "not": { "enum": [1, 'A'] }

Meta Overrides

The following may be provided on a joi .meta() object to explicitly override default joi-to-schema behavior.

className: By default J2S will be full verbose in its components. If an object has a className string, J2S will look for an existing schema component with that name, and if a component does not exist then it will create one. Either way, it will produce a $ref element for that schema component. If a new component is created it will be returned with the swagger schema.

classTarget: Named components are assumed to be schemas, and are referenced as components/schemas/ComponentName. If a classTarget meta value is provided (such as parameters), this will replace schemas in the reference.

swagger: To explicitly define your own swagger component for a joi schema object, place that swagger object in the swagger meta tag. It will be mixed in to the schema that J2S produces.

swaggerOverride: If this meta tag is truthy, the swagger component will replace the result for that schema instead of mixing in to it.

swaggerType: Can be used with the .any() type to add files.

schemaOverride: A replacement Joi schema which is used to generate swagger. For example, AWS API Gateway supports a subset of the swagger spec. In order to utilize this library with AWS API Gateway's swagger, this option is useful when working with Joi.alternatives().

The example below uses joi.when, which would normally use oneOf, anyOf, or allOf keywords. In order to get around that, the meta tag overrides the schema to be similar, but less strict.

  type: joi.string().valid('a', 'b'),
  body: when('type', {
    is: 'a',
    then: joi.object({ a: joi.string() }),
    otherwise: when('type', {
      is: 'b',
      then: joi.object({ b: joi.string() }),
      otherwise: joi.forbidden()
}).meta({ schemaOverride: joi.object({ a: joi.string(), b: joi.string() })})

refValues: The possibility to give exact values when using joi.ref()

  durationFrom: joi.number().integer().min(5).max(10),
  durationTo: joi.number().integer().min(joi.ref('durationFrom')).max(20)
    .meta({ refValues: { durationFrom: 5 } }),

Custom Types (joi.extend)

For supporting custom joi types you can add the needed type information using a the meta property baseType.

const customJoi = joi.extend({
    type: 'customStringType',
    base: joi.string().meta({ baseType: 'string' }),
    // ...

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