---
'@backstage/plugin-catalog-backend': minor
---

This feature works the same as \$secret does in config - it allows programmatic substitution of values into a document.

This is particularly useful e.g. for API type entities where you do not want to repeat your entire API spec document inside the catalog-info.yaml file. For those cases, you can instead do something like

```
apiVersion: backstage.io/v1alpha1
kind: API
metadata:
  name: my-federated-service
spec:
  type: graphql
  definition:
    $text: ./schema.graphql
```

The textual content of that file will be injected as the value of definition, during each refresh loop. Both relative and absolute paths are supported, as well as any HTTP/HTTPS URL pointing to a service that returns the relevant data.

The initial version supports injection of text file data, and structured data from JSON and YAML files. You can add any handler of your own in addition to these.