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+# 🦋 express-openapi-validator
+
+**An OpenApi validator for ExpressJS** that automatically validates **API** _**requests**_ and _**responses**_ using an **OpenAPI 3** specification.
+
+[🦋express-openapi-validator](https://github.com/cdimascio/express-openapi-validator) is an unopinionated library that integrates with new and existing API applications. express-openapi-validator lets you write code the way you want; it does not impose any coding convention or project layout. Simply, install the validator onto your express app, point it to your OpenAPI 3 specification, then define and implement routes the way you prefer. See an [example](#example-express-api-server).
+
+**Features:**
+
+- ✔️ request validation
+- ✔️ response validation (json only)
+- 👮 security validation / custom security functions
+- 👽 3rd party / custom formats
+- 🧵 optionally auto-map OpenAPI endpoints to Express handler functions
+- ✂️ **\$ref** support; split specs over multiple files
+- 🎈 file upload
+
+## Install
+
+```shell
+npm install express-openapi-validator
+```
+
+## Usage
+
+1. Require/import the openapi validator
+
+```javascript
+const OpenApiValidator = require('express-openapi-validator');
+```
+
+2. Install the middleware
+
+```javascript
+app.use(
+  OpenApiValidator.middleware({
+    apiSpec: './openapi.yaml',
+    validateRequests: true, // (default)
+    validateResponses: true, // false by default
+  }),
+);
+```
+
+3. Register an error handler
+
+```javascript
+app.use((err, req, res, next) => {
+  // format error
+  res.status(err.status || 500).json({
+    message: err.message,
+    errors: err.errors,
+  });
+});
+```
+
+_**Important:** Ensure express is configured with all relevant body parsers. Body parser middleware functions must be specified prior to any validated routes. See an [example](#example-express-api-server)_.