# Compression

Source: https://docs.nestjs.com/http/compression

Compression can significantly reduce the size of the response body, which makes a web app faster to load.

For **high-traffic** websites in production, we strongly recommend offloading compression from the application server, typically to a reverse proxy (e.g., Nginx). In that case, don't use compression middleware.

#### Use with Express (default)

Use the [compression](https://github.com/expressjs/compression) middleware package to enable response compression. It supports the gzip, deflate, and Brotli encodings, and picks one based on the request's `Accept-Encoding` header.

First, install the required packages:

```bash
$ npm i --save compression
$ npm i --save-dev @types/compression
```

Once the installation is complete, apply the compression middleware globally:

```typescript
import compression from 'compression';
// somewhere in your initialization file
app.use(compression());
```

#### Use with Fastify

If you use the `FastifyAdapter`, use the [@fastify/compress](https://github.com/fastify/fastify-compress) plugin instead:

```bash
$ npm i --save @fastify/compress
```

Once the installation is complete, register the `@fastify/compress` plugin. It compresses all eligible responses by default.

> warning **Warning** Make sure you pass the `NestFastifyApplication` type when creating the application. Otherwise, the `register()` method isn't available to apply the plugin.

```typescript
import { FastifyAdapter, NestFastifyApplication } from '@nestjs/platform-fastify';

import compression from '@fastify/compress';

// inside bootstrap()
const app = await NestFactory.create<NestFastifyApplication>(AppModule, new FastifyAdapter());
await app.register(compression);
```

By default, `@fastify/compress` uses the first encoding the client accepts, in this order of preference: `zstd` (on Node.js versions that support it), `br` (Brotli), `gzip`, and `deflate`. Brotli achieves a high compression ratio, but higher quality levels are slow. The plugin sets the Brotli quality (`BROTLI_PARAM_QUALITY`) to 4 by default instead of zlib's default of 11. You can set it anywhere from 0 (fastest) to 11 (smallest output), trading compression time against response size. Tune this value for your workload. The following example sets the quality explicitly:

```typescript
import { constants } from 'node:zlib';
// somewhere in your initialization file
await app.register(compression, { brotliOptions: { params: { [constants.BROTLI_PARAM_QUALITY]: 4 } } });
```

Alternatively, you can restrict `@fastify/compress` to gzip and deflate. Responses may be larger, but they are compressed faster.

To specify the encodings, pass the `encodings` option in the second argument to `app.register()`:

```typescript
await app.register(compression, { encodings: ['gzip', 'deflate'] });
```

This configuration tells `@fastify/compress` to use only the gzip and deflate encodings, preferring gzip when the client supports both.