> ## Documentation Index
> Fetch the complete documentation index at: https://braintrust.dev/docs/llms.txt
> Use this file to discover all available pages before exploring further.
# Custom view code cannot use package imports
export const plans_0 = "Any"
export const deployments_0 = "Any"
export const data_plane_version_0 = undefined
export const use_case_0 = "Use case - Building custom views or visualizations that rely on external package imports"
**Applies to:**
* Plan - {plans_0}
* Deployment - {deployments_0}
* {data_plane_version_0}
* {use_case_0}
## Summary
**Issue:** Custom view code that uses `import` or `require` statements fails silently — external packages are unavailable at runtime.
**Cause:** The custom view sandbox explicitly strips all `import` and `require` calls before executing code. This is a security measure because Braintrust cannot validate arbitrary third-party code.
**Resolution:** Rewrite the component without external dependencies, or use the span iframes feature to render custom content with full access to external libraries.
## How custom view code execution works
### Security sandbox environment
Custom views run in an isolated sandbox, completely separate from your local project environment. The sandbox receives only your component code, trace data, and span data via `postMessage` communication.
Before execution, the sandbox preprocessor automatically strips all `import` and `require` statements from your code. Any references to imported modules will throw runtime errors since the modules are never loaded.
### Available APIs and libraries
The sandbox provides access to:
* Native browser APIs (Canvas, SVG, DOM manipulation, fetch)
* React primitives and hooks
* A small set of pre-bundled libraries (exact list not publicly documented)
Your local `node_modules` directory and any packages you've installed are not accessible to custom view code.
### Alternative for external dependencies
For visualizations requiring external libraries like D3, Recharts, or domain-specific packages, use the [span iframes feature](https://www.braintrust.dev/docs/instrument/advanced-tracing#customize-span-rendering) instead.
Span iframes render a fully custom HTML page inside the trace view. You control the entire document, so you can load external scripts via CDN `