> ## Documentation Index
> Fetch the complete documentation index at: https://developers.hubspot.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

---
id: d0b583d7-a30b-4dc0-877f-776c7eaf2ed9
---

# Build health checks

> Learn how HubSpot's CMS React platform uses build health checks in your CMS React project.

<RelatedApiLink />

To validate and prevent unexpected production behavior, HuSpot will automatically run a series of health checks at the end of a build for a CMS React project. These health checks are enabled but will not fail a build by default.

Build health checks look for the following:

* For every React module, HubSpot verifies that:
  * The built module code can be imported.
  * There is a `Component` named export and that it is a React component (a function).
  * There is a `fields` named export and that it is a React element (`<ModuleFields>...</ModuleFields>`) or an array.
  * There is a `meta` named export and it is a JavaScript object.
* For any island import (`?island`), client import (`?client`) or dynamic import (`import(...)`) linked from a React module's code, the code must be able to be imported.

Failed health checks are logged in the build output only when strict health checks are enabled.

## ESM and Common JS

In addition to verifying React modules, health checks will also uncover problematic [ESM and Common JS issues](https://yuzu.health/blog/cjs-vs-esm) before any code is deployed.

HubSpot's CMS React system is built on top of [Vite](https://vitejs.dev/), which can lead to complications when depending on other package that have misconfigured ESM exports. Relatedly, some packages that advertise CJS exports (i.e., `package.json` `export` / `type`) may actually include ESM `import` and `export` syntax (e.g., [`@mui/material@5.15.10`](https://publint.dev/@mui/material@5.15.10)). This can lead to situations where Vite's compiler outputs an import to that package's file in a `node/modules...`, which results in a runtime syntax error when the code is run. However, with build health checks, HubSpot can ensure that the problem is discovered at build-time rather than by visitors at runtime.

## Build health check configuration

To explicitly configure your project's build health checks, you can update the `cms-assets.json` file.

```json theme={null}
{
  "label": "My CMS project",
  "buildConfig": {
    "healthchecks": {
      "enabled": true,
      "strict": true
    }
  }
};
```