openapi-to-typescript

•

24.4k23983 months ago

Converts OpenAPI 3.0 JSON/YAML to TypeScript interfaces and type guards. This skill should be used when the user asks to generate types from OpenAPI, convert schema to TS, create API interfaces, or generate TypeScript types from an API specification.

Quick Install

npxskills add davila7/claude-code-templates--skill openapi-to-typescript

Instructions

OpenAPI to TypeScript

Converts OpenAPI 3.0 specifications to TypeScript interfaces and type guards.

Input: OpenAPI file (JSON or YAML) Output: TypeScript file with interfaces and type guards

When to Use

"generate types from openapi"
"convert openapi to typescript"
"create API interfaces"
"generate types from spec"

Workflow

Request the OpenAPI file path (if not provided)
Read and validate the file (must be OpenAPI 3.0.x)
Extract schemas from components/schemas
Extract endpoints from paths (request/response types)
Generate TypeScript (interfaces + type guards)
Ask where to save (default: types/api.ts in current directory)
Write the file

OpenAPI Validation

Check before processing:

- Field "openapi" must exist and start with "3.0"
- Field "paths" must exist
- Field "components.schemas" must exist (if there are types)

If invalid, report the error and stop.

Type Mapping

Primitives

OpenAPI	TypeScript
`string`	`string`
`number`	`number`
`integer`	`number`
`boolean`	`boolean`
`null`

Format Modifiers

Format	TypeScript
`uuid`	`string` (comment UUID)
`date`	`string` (comment date)
`date-time`	`string` (comment ISO)
`email`	`string` (comment email)
`uri`

Complex Types

Object:

// OpenAPI: type: object, properties: {id, name}, required: [id]
interface Example {
  id: string;      // required: no ?
  name?: string;   // optional: with ?
}

Array:

// OpenAPI: type: array, items: {type: string}
type Names = string[];

Enum:

// OpenAPI: type: string, enum: [active, draft]
type Status = "active" | "draft";

oneOf (Union):

// OpenAPI: oneOf: [{$ref: Cat}, {$ref: Dog}]
type Pet = Cat | Dog;

allOf (Intersection/Extends):

// OpenAPI: allOf: [{$ref: Base}, {type: object, properties: ...}]
interface Extended extends Base {
  extraField: string;
}

Code Generation

File Header

/**
 * Auto-generated from: {source_file}
 * Generated at: {timestamp}
 *
 * DO NOT EDIT MANUALLY - Regenerate from OpenAPI schema
 */

Interfaces (from components/schemas)

For each schema in components/schemas:

export interface Product {
  /** Product unique identifier */
  id: string;

  /** Product title */
  title: string;

  /** Product price */
  price: number;

  /** Created timestamp */
  created_at?: string;
}

Use OpenAPI description as JSDoc
Fields in required[] have no ?
Fields outside required[] have ?

Request/Response Types (from paths)

For each endpoint in paths:

// GET /products - query params
export interface GetProductsRequest {
  page?: number;
  limit?: number;
}

// GET /products - response 200
export type GetProductsResponse = ProductList;

// POST /products - request body
export interface CreateProductRequest {
  title: string;
  price: number;
}

// POST /products - response 201
export type CreateProductResponse = Product;

Naming convention:

{Method}{Path}Request for params/body
{Method}{Path}Response for response

Type Guards

For each main interface, generate a type guard:

export function isProduct(value: unknown): value is Product {
  return (
    typeof value === 'object' &&
    value !== null &&
    'id' in value &&
    typeof (value as any).id === 'string' &&
    'title' in value &&
    typeof (value as any).title === 'string' &&
    'price' in value &&
    typeof (value as any).price === 'number'
  );
}

Type guard rules:

Check typeof value === 'object' && value !== null
For each required field: check 'field' in value
For primitive fields: check typeof
For arrays: check Array.isArray()
For enums: check .includes()

Error Type (always include)

export interface ApiError {
  status: number;
  error: string;
  detail?: string;
}

export function isApiError(value: unknown): value is ApiError {
  return (
    typeof value === 'object' &&
    value !== null &&
    'status' in value &&
    typeof (value as any).status === 'number' &&
    'error' in value &&
    typeof (value as any).error === 'string'
  );
}

$ref Resolution

When encountering {"$ref": "#/components/schemas/Product"}:

Extract the schema name (Product)
Use the type directly (don't resolve inline)

// OpenAPI: items: {$ref: "#/components/schemas/Product"}
// TypeScript:
items: Product[]  // reference, not inline

Complete Example

Input (OpenAPI):

{
  "openapi": "3.0.0",
  "components": {
    "schemas": {
      "User": {
        "type": "object",
        "properties": {
          "id": {"type": "string", "format": "uuid"},
          "email": {"type": "string", "format": "email"},
          "role": {"type": "string", "enum": ["admin", "user"]}
        },
        "required": ["id", "email", "role"]
      }
    }
  },
  "paths": {
    "/users/{id}": {
      "get": {
        "parameters": [{"name": "id", "in": "path", "required": true}],
        "responses": {
          "200": {
            "content": {
              "application/json": {
                "schema": {"$ref": "#/components/schemas/User"}
              }
            }
          }
        }
      }
    }
  }
}

Output (TypeScript):

/**
 * Auto-generated from: api.openapi.json
 * Generated at: 2025-01-15T10:30:00Z
 *
 * DO NOT EDIT MANUALLY - Regenerate from OpenAPI schema
 */

// ============================================================================
// Types
// ============================================================================

export type UserRole = "admin" | "user";

export interface User {
  /** UUID */
  id: string;

  /** Email */
  email: string;

  role: UserRole;
}

// ============================================================================
// Request/Response Types
// ============================================================================

export interface GetUserByIdRequest {
  id: string;
}

export type GetUserByIdResponse = User;

// ============================================================================
// Type Guards
// ============================================================================

export function isUser(value: unknown): value is User {
  return (
    typeof value === 'object' &&
    value !== null &&
    'id' in value &&
    typeof (value as any).id === 'string' &&
    'email' in value &&
    typeof (value as any).email === 'string' &&
    'role' in value &&
    ['admin', 'user'].includes((value as any).role)
  );
}

// ============================================================================
// Error Types
// ============================================================================

export interface ApiError {
  status: number;
  error: string;
  detail?: string;
}

export function isApiError(value: unknown): value is ApiError {
  return (
    typeof value === 'object' &&
    value !== null &&
    'status' in value &&
    typeof (value as any).status === 'number' &&
    'error' in value &&
    typeof (value as any).error === 'string'
  );
}

Common Errors

Error	Action
OpenAPI version != 3.0.x	Report that only 3.0 is supported
$ref not found	List missing refs
Unknown type	Use `unknown` and warn
Circular reference	Use type alias with lazy reference

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