---
title: Use default or custom attributes (C SDK)
source: https://docs.newrelic.com/docs/apm/agents/c-sdk/instrumentation/use-default-or-custom-attributes-c-sdk
---

> #### ⚠️ EOL NOTICE
>
> From April 2022, we don't support the C SDK capability. For more details, see our [Support Forum post](https://support.newrelic.com/s/hubtopic/aAX8W0000008d0r/q1-bulk-eol-announcement-fy23).

In New Relic, **attributes** are key-value pairs containing information that determines the properties of an [event](https://docs.newrelic.com/docs/accounts-partnerships/getting-started-new-relic/glossary#event) or [transaction](https://docs.newrelic.com/docs/accounts-partnerships/getting-started-new-relic/glossary#transaction). These key-value pairs can help you gain greater insight into your application and [query your data](https://docs.newrelic.com/docs/query-your-data/explore-query-data/query-builder/introduction-query-builder).

## View and use attributes [#locations]

Both [default APM attributes](https://docs.newrelic.com/docs/insights/new-relic-insights/decorating-events/apm-default-attributes-insights#transaction-event) and [custom attributes](https://docs.newrelic.com/docs/agents/manage-apm-agents/agent-data/collect-custom-attributes) for your C application appear in:

-   APM [transaction traces](https://docs.newrelic.com/docs/apm/transactions/transaction-traces/introduction-transaction-traces) and [error analytics](https://docs.newrelic.com/docs/apm/applications-menu/error-analytics/introduction-error-analytics)
-   [APM events](https://docs.newrelic.com/docs/insights/explore-data/attributes/apm-default-attributes-insights)

## C-specific attributes [#attributes]

> #### ⚠️ IMPORTANT
>
> Before creating custom attributes, review New Relic's list of [reserved terms used by NRQL](https://docs.newrelic.com/docs/insights/insights-data-sources/custom-data/insights-custom-data-requirements-limits#reserved-words). Otherwise unexpected results may occur.

To add custom attributes to your C application, call one of [the attribute functions in the C SDK API](https://newrelic.github.io/c-sdk/libnewrelic_8h.html#abfe6f64a8eec7d60d8588f8969781d34); for example, `newrelic_add_attribute_double()`. The key name for your custom attribute depends on what you specify when you call the function.