---
title: "declare block | Grafana Agent documentation"
description: "Learn about the declare configuration block"
---

> For a curated documentation index, see [llms.txt](/llms.txt). For the complete documentation index, see [llms-full.txt](/llms-full.txt).

# declare block

`declare` is an optional configuration block used to define a new \[custom component]\[]. `declare` blocks must be given a label that determines the name of the custom component.

## Example

Alloy ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```alloy
declare "COMPONENT_NAME" {
    COMPONENT_DEFINITION
}
```

## Arguments

The `declare` block has no predefined schema for its arguments. The body of the `declare` block is used as the component definition. The body can contain the following:

- [argument](/docs/agent/latest/flow/reference/config-blocks/argument/) blocks
- [export](/docs/agent/latest/flow/reference/config-blocks/export/) blocks
- [declare](/docs/agent/latest/flow/reference/config-blocks/declare/) blocks
- [import](/docs/agent/latest/flow/concepts/modules/#importing-modules) blocks
- Component definitions (either built-in or custom components)

The `declare` block may not contain any configuration blocks that aren’t listed above.

## Exported fields

The `declare` block has no predefined schema for its exports. The fields exported by the `declare` block are determined by the [export blocks](/docs/agent/latest/flow/reference/config-blocks/export/) found in its definition.

## Example

This example creates and uses a custom component that self-collects process metrics and forwards them to an argument specified by the user of the custom component:

Alloy ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```alloy
declare "self_collect" {
  argument "metrics_output" {
    optional = false
    comment  = "Where to send collected metrics."
  }

  prometheus.scrape "selfmonitor" {
    targets = [{
      __address__ = "127.0.0.1:12345",
    }]

    forward_to = [argument.metrics_output.value]
  }
}

self_collect "example" {
  metrics_output = prometheus.remote_write.example.receiver
}

prometheus.remote_write "example" {
  endpoint {
    url = REMOTE_WRITE_URL
  }
}
```