# Values Schemas, CRDs and Library Charts — Helm

Source: https://www.skillbyai.com/en/helm/a-schema

> Validate values with JSON Schema, handle CRDs correctly and share helpers in library charts.

## Guardrails for chart users

A **`values.schema.json`** file in the chart root describes allowed values with JSON Schema; Helm validates merged values against it during `install`, `upgrade`, `lint` and `template`, so a typo like `replicaCont` or a string where a number belongs fails immediately with a clear message. **CRDs** placed in the `crds/` directory are installed before other resources on first install, but Helm **never upgrades or deletes** them, by design, because deleting a CRD deletes every custom resource of that type. Charts that must upgrade CRDs often ship them as templates or as a separate chart instead. A **library chart** (`type: library`) contains only named templates, such as standard labels or a common Deployment shape, for other charts to include; it cannot be installed itself. The annotation **`helm.sh/resource-policy: keep`** tells Helm to leave a resource (such as a PersistentVolumeClaim) in place on uninstall.

## A small values schema

Wrong types, unknown keys and missing required fields fail before anything reaches the cluster.

```json
{
  "$schema": "https://json-schema.org/draft-07/schema#",
  "type": "object",
  "required": ["image", "apiUrl"],
  "properties": {
    "replicaCount": { "type": "integer", "minimum": 1 },
    "apiUrl": { "type": "string", "pattern": "^https://" },
    "image": {
      "type": "object",
      "required": ["repository"],
      "properties": {
        "repository": { "type": "string" },
        "tag": { "type": "string" }
      },
      "additionalProperties": false
    }
  }
}
```

## Uninstall can delete your data

PersistentVolumeClaims created by a release are deleted on `helm uninstall` unless they carry `helm.sh/resource-policy: keep` or come from a StatefulSet's volume claim templates. Check before uninstalling anything stateful.

**Quiz:** What happens to CRDs in a chart's crds/ directory when you run helm upgrade?

- [ ] They are upgraded to the new definition
- [ ] They are deleted and recreated
- [x] They are not upgraded; Helm only installs them on first install
- [ ] They are converted to templates

*Answer:* They are not upgraded; Helm only installs them on first install. Helm installs crds/ content once and never upgrades or deletes it, to protect custom resources.