> ## Documentation Index
> Fetch the complete documentation index at: https://logixlysia-claude-elysia-v2-open-beta-i2faib.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Request ID

> Generate or honor unique request identifiers across requests and responses

Logixlysia can automatically generate or retrieve unique request identifiers (Request IDs) and attach them to the request context, response headers, and log outputs.

## Basic Usage

You can enable the request ID feature using the `requestId` config option. When set to `true`, it uses the default configuration (`X-Request-Id` header and UUID v4 generator).

```ts theme={null}
import { Elysia } from 'elysia'
import logixlysia from 'logixlysia'

const app = new Elysia()
  .use(
    logixlysia({
      config: {
        requestId: true
      }
    })
  )
```

## Production Preset

The `prod` preset enables `requestId` automatically by default:

```ts theme={null}
const app = new Elysia()
  .use(
    logixlysia({
      preset: 'prod' // requestId is enabled automatically
    })
  )
```

## Custom Configuration

For advanced use cases, you can pass a configuration object instead of a boolean:

```ts theme={null}
const app = new Elysia()
  .use(
    logixlysia({
      config: {
        requestId: {
          // Custom header name to read from / write to
          header: 'X-Correlation-Id',
          // Custom request ID generator function
          generator: () => `req-${crypto.randomUUID()}`
        }
      }
    })
  )
```

### Options

| Option      | Type           | Default             | Description                                                                                       |
| ----------- | -------------- | ------------------- | ------------------------------------------------------------------------------------------------- |
| `enabled`   | `boolean`      | `true`              | Turn request ID generation on or off when using object configuration.                             |
| `header`    | `string`       | `'X-Request-Id'`    | The header key to check on incoming requests (honoring upstream proxies) and to set on responses. |
| `generator` | `() => string` | `crypto.randomUUID` | A function that returns a unique string to use as the request ID.                                 |

## Log Formatting

When Request ID is enabled, you can output it in your custom log format using the `{requestId}` token:

```ts theme={null}
const app = new Elysia()
  .use(
    logixlysia({
      config: {
        requestId: true,
        customLogFormat: '{method} {pathname} - Request ID: {requestId}'
      }
    })
  )
```

If Request ID is disabled or not present, the token will render as an empty string.

## Error Responses

If a request fails (e.g. throws an exception), the request ID is still propagated in the response headers (like `X-Request-Id`) and is correctly logged in the HTTP error telemetry context, allowing trace correlation for failed requests.