The Standard Schema project is a set of interfaces that standardize the provision and consumption of shared functionality in the TypeScript ecosystem.

Its goal is to allow tools to accept a single input that includes all the types and capabilities they need— no library-specific adapters, no extra dependencies. The result is an ecosystem that's fair for implementers, friendly for consumers, and open for end users.

The specifications

The specifications can be found below in their entirety. Libraries wishing to implement a spec can copy/paste the code block below into their codebase. They're also available at @standard-schema/spec on npm and JSR.

// #########################
// ###   Standard Typed  ###
// #########################

/** The Standard Typed interface. This is a base type extended by other specs. */
export interface StandardTypedV1<Input = unknown, Output = Input> {
  /** The Standard properties. */
  readonly "~standard": StandardTypedV1.Props<Input, Output>;
}

export declare namespace StandardTypedV1 {
  /** The Standard Typed properties interface. */
  export interface Props<Input = unknown, Output = Input> {
    /** The version number of the standard. */
    readonly version: 1;
    /** The vendor name of the schema library. */
    readonly vendor: string;
    /** Inferred types associated with the schema. */
    readonly types?: Types<Input, Output> | undefined;
  }

  /** The Standard Typed types interface. */
  export interface Types<Input = unknown, Output = Input> {
    /** The input type of the schema. */
    readonly input: Input;
    /** The output type of the schema. */
    readonly output: Output;
  }

  /** Infers the input type of a Standard Typed. */
  export type InferInput<Schema extends StandardTypedV1> = NonNullable<
    Schema["~standard"]["types"]
  >["input"];

  /** Infers the output type of a Standard Typed. */
  export type InferOutput<Schema extends StandardTypedV1> = NonNullable<
    Schema["~standard"]["types"]
  >["output"];
}

// ##########################
// ###   Standard Schema  ###
// ##########################

/** The Standard Schema interface. */
export interface StandardSchemaV1<Input = unknown, Output = Input> {
  /** The Standard Schema properties. */
  readonly "~standard": StandardSchemaV1.Props<Input, Output>;
}

export declare namespace StandardSchemaV1 {
  /** The Standard Schema properties interface. */
  export interface Props<Input = unknown, Output = Input>
    extends StandardTypedV1.Props<Input, Output> {
    /** Validates unknown input values. */
    readonly validate: (
      value: unknown,
      options?: StandardSchemaV1.Options | undefined
    ) => Result<Output> | Promise<Result<Output>>;
  }

  /** The result interface of the validate function. */
  export type Result<Output> = SuccessResult<Output> | FailureResult;

  /** The result interface if validation succeeds. */
  export interface SuccessResult<Output> {
    /** The typed output value. */
    readonly value: Output;
    /** A falsy value for `issues` indicates success. */
    readonly issues?: undefined;
  }

  export interface Options {
    /** Explicit support for additional vendor-specific parameters, if needed. */
    readonly libraryOptions?: Record<string, unknown> | undefined;
  }

  /** The result interface if validation fails. */
  export interface FailureResult {
    /** The issues of failed validation. */
    readonly issues: ReadonlyArray<Issue>;
  }

  /** The issue interface of the failure output. */
  export interface Issue {
    /** The error message of the issue. */
    readonly message: string;
    /** The path of the issue, if any. */
    readonly path?: ReadonlyArray<PropertyKey | PathSegment> | undefined;
  }

  /** The path segment interface of the issue. */
  export interface PathSegment {
    /** The key representing a path segment. */
    readonly key: PropertyKey;
  }

  /** The Standard types interface. */
  export interface Types<Input = unknown, Output = Input>
    extends StandardTypedV1.Types<Input, Output> {}

  /** Infers the input type of a Standard. */
  export type InferInput<Schema extends StandardTypedV1> =
    StandardTypedV1.InferInput<Schema>;

  /** Infers the output type of a Standard. */
  export type InferOutput<Schema extends StandardTypedV1> =
    StandardTypedV1.InferOutput<Schema>;
}

// ###############################
// ###   Standard JSON Schema  ###
// ###############################

/** The Standard JSON Schema interface. */
export interface StandardJSONSchemaV1<Input = unknown, Output = Input> {
  /** The Standard JSON Schema properties. */
  readonly "~standard": StandardJSONSchemaV1.Props<Input, Output>;
}

export declare namespace StandardJSONSchemaV1 {
  /** The Standard JSON Schema properties interface. */
  export interface Props<Input = unknown, Output = Input>
    extends StandardTypedV1.Props<Input, Output> {
    /** Methods for generating the input/output JSON Schema. */
    readonly jsonSchema: StandardJSONSchemaV1.Converter;
  }

  /** The Standard JSON Schema converter interface. */
  export interface Converter {
    /** Converts the input type to JSON Schema. May throw if conversion is not supported. */
    readonly input: (
      options: StandardJSONSchemaV1.Options
    ) => Record<string, unknown>;
    /** Converts the output type to JSON Schema. May throw if conversion is not supported. */
    readonly output: (
      options: StandardJSONSchemaV1.Options
    ) => Record<string, unknown>;
  }

  /**
   * The target version of the generated JSON Schema.
   *
   * It is *strongly recommended* that implementers support `"draft-2020-12"` and `"draft-07"`, as they are both in wide use. All other targets can be implemented on a best-effort basis. Libraries should throw if they don't support a specified target.
   *
   * The `"openapi-3.0"` target is intended as a standardized specifier for OpenAPI 3.0 which is a superset of JSON Schema `"draft-04"`.
   */
  export type Target =
    | "draft-2020-12"
    | "draft-07"
    | "openapi-3.0"
    // Accepts any string for future targets while preserving autocomplete
    | ({} & string);

  /** The options for the input/output methods. */
  export interface Options {
    /** Specifies the target version of the generated JSON Schema. Support for all versions is on a best-effort basis. If a given version is not supported, the library should throw. */
    readonly target: Target;

    /** Explicit support for additional vendor-specific parameters, if needed. */
    readonly libraryOptions?: Record<string, unknown> | undefined;
  }

  /** The Standard types interface. */
  export interface Types<Input = unknown, Output = Input>
    extends StandardTypedV1.Types<Input, Output> {}

  /** Infers the input type of a Standard. */
  export type InferInput<Schema extends StandardTypedV1> =
    StandardTypedV1.InferInput<Schema>;

  /** Infers the output type of a Standard. */
  export type InferOutput<Schema extends StandardTypedV1> =
    StandardTypedV1.InferOutput<Schema>;
}