# ParamMetadata

**Kind:** Interface

**Source:** [`packages/core/helpers/interfaces/params-metadata.interface.ts`](https://github.com/nestjs/nest/blob/master/packages/core/helpers/interfaces/params-metadata.interface.ts#L4)

**Part of:** [Core](subsystem-packages-core)

`ParamMetadata` describes metadata for a single parameter in a handler, resolver, or decorated method. It stores the parameter's positional `index` and associated `data`, allowing the framework to resolve and inject the correct value at runtime.

## Properties

| Property | Type |
|---|---|
| `index` | `number` |
| `data` | `ParamData` |

## Diagram

```mermaid
graph LR
  Handler[Handler Method] --> Params[Parameter List]
  Params --> Metadata[ParamMetadata]
  Metadata --> Index[index: number]
  Metadata --> Data[data: ParamData]
  Metadata --> Resolver[Parameter Resolver]
```

## Usage

```ts
import type { ParamMetadata } from './helpers/interfaces/params-metadata.interface';

const userIdParam: ParamMetadata = {
  index: 0,
  data: {
    name: 'userId',
    type: 'param',
  },
};

function resolveParameter(metadata: ParamMetadata, request: Request) {
  if (metadata.data.type === 'param') {
    return request.params[metadata.data.name];
  }

  return undefined;
}

const userId = resolveParameter(userIdParam, request);
```

## AI Coding Instructions

- Keep `index` aligned with the parameter's zero-based position in the target method signature.
- Use the appropriate `ParamData` shape when creating metadata; avoid replacing it with untyped objects.
- Preserve parameter metadata ordering when collecting metadata for a method or resolver.
- Use `ParamMetadata` with the parameter-resolution pipeline rather than reading request or context values directly in framework internals.