> For the complete documentation index, see [llms.txt](https://doc.wearepatchworks.com/product-documentation/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://doc.wearepatchworks.com/product-documentation/process-flows/building-process-flows/dynamic-variables/metadata-variables.md).

# Metadata variables

## Introduction

Payload metadata variables (known as meta-variables) can be added by [custom scripts](/product-documentation/marketplace/marketplace-scripts.md) and the [set variables](/product-documentation/process-flows/building-process-flows/process-flow-shapes/standard-shapes/set-variables-shape.md) shape.

There may be times when you need to define variables or parameters for a process flow step using values from the incoming payload metadata. This can be achieved using a specific payload syntax in the process flow connection shape.

## Need to know

* Payload metadata cannot exceed 10240 bytes. Exceeding this limit will cause the process flow to fail on the associated step.
* Meta-variable values are `string` values.

## Referencing meta variables

Payload metadata can be accessed via a variable or parameter field using the syntax below:

```
[[meta.unique_key]]
```

For example:

```
[[meta.id]]
```

![](/files/UlDPULF3snGYHhd4ppa7)

{% hint style="info" %}
When defining variables you can 'mix and match' [payload](#variables-and-parameters-from-payload-syntax), **metadata** and [flow](/product-documentation/process-flows/building-process-flows/dynamic-variables/flow-variables.md) variables. For example:

<img src="/files/0i35OD1HXancx84C0Z3s" alt="" data-size="original">
{% endhint %}

{% hint style="info" %}
When a payload is passed to a 'child' process flow via the [run process flow shape](/product-documentation/process-flows/building-process-flows/process-flow-shapes/standard-shapes/run-process-flow-shape.md), meta variables are included.
{% endhint %}

## Related information

* [Payload variables](/product-documentation/process-flows/building-process-flows/dynamic-variables/payload-variables.md)
* [Flow variables](/product-documentation/process-flows/building-process-flows/dynamic-variables/flow-variables.md)
* [Generating dynamic cache keys with variables](/product-documentation/process-flows/building-process-flows/process-flow-shapes/advanced-shapes/cache/add-to-cache-shape/generating-dynamic-cache-keys-with-variables.md)