> ## Documentation Index
> Fetch the complete documentation index at: https://docs.apitally.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Attributes

> Span attributes available to callbacks in the Apitally SDK for JavaScript.

In the Apitally SDK, each API request is represented by a span. Span attributes contain metadata about the request and response, such as the request path, HTTP method, and response status code.

You can use this metadata to make decisions in [sampling](/sdk-reference/javascript/v1/sampling#custom-sampling) and [masking](/sdk-reference/javascript/v1/masking#body-masking-callbacks) callbacks, which receive the `span` object as an argument. Access attributes through `span.attributes`. Individual attributes might be missing, so use bracket notation and handle `undefined`:

```javascript {2-3} theme={null}
function callback(span) {
  const attributes = span.attributes;
  const path = attributes["url.path"];
  // ...
}
```

## Default attributes

The following attributes are useful for common callback decisions. The list is not exhaustive.

| Attribute                      | Type     | Description                                           |
| :----------------------------- | :------- | :---------------------------------------------------- |
| `http.request.method`          | `string` | HTTP method, e.g. `GET` or `POST`.                    |
| `url.path`                     | `string` | Request path, e.g. `/users/123`.                      |
| `url.query`                    | `string` | Query string without `?`, e.g. `page=2`.              |
| `user_agent.original`          | `string` | Value of the `User-Agent` header.                     |
| `http.route`                   | `string` | Matched endpoint route pattern, e.g. `/users/:id`.    |
| `http.response.status_code`    | `number` | HTTP response status code, e.g. `200` or `404`.       |
| `apitally.consumer.identifier` | `string` | Consumer identifier supplied via `setConsumer()`.     |
| `apitally.consumer.group`      | `string` | Optional consumer group supplied via `setConsumer()`. |

## Set custom attributes

Use `setRequestAttribute()` in your request handling code to attach custom metadata to the current request span. These attributes are included in the request trace and available to response-stage sampling and masking callbacks.

```javascript theme={null}
import { setRequestAttribute } from "apitally";

setRequestAttribute("tenant.id", tenantId);
```