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Content Security Policy (CSP) controls which domains your widgets can fetch from, load scripts/styles from, and embed. Widgets run in sandboxed iframes, so CSP must explicitly allow any external resources.

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Automatic Configuration

When baseUrl is set (via MCPServer constructor or MCP_URL environment variable), mcp-use automatically configures CSP: 
const server = new MCPServer({
  name: "my-server",
  version: "1.0.0",
  baseUrl: process.env.MCP_URL, // Required for production
});
This ensures:
  • Widget URLs use the correct domain
  • CSP includes your server domain
  • Works behind proxies and custom domains
The server origin is auto-injected into each widget’s connectDomains, resourceDomains, and baseUriDomains—you don’t need to add it manually.

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Per-Widget Configuration

For widgets that need additional domains (APIs, CDNs, etc.), configure CSP in your widget metadata.

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MCP Apps (all compatible clients, ChatGPT, Claude etc..)

With type: "mcpApps", use camelCase in metadata.csp: 
export const widgetMetadata: WidgetMetadata = {
  description: "Display weather",
  props: propSchema,
  metadata: {
    csp: {
      connectDomains: ["https://api.weather.com"],
      resourceDomains: ["https://cdn.weather.com"],
      baseUriDomains: ["https://myserver.com"],
      frameDomains: ["https://trusted-embed.com"],
      redirectDomains: ["https://oauth.provider.com"],
    },
  },
};

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Apps SDK Format (ChatGPT only - DEPRECATED)

With type: "appsSdk", use snake_case in appsSdkMetadata["openai/widgetCSP"]: 
export const appsSdkMetadata = {
  "openai/widgetCSP": {
    connect_domains: ["https://api.weather.com"],
    resource_domains: ["https://cdn.weather.com"],
    frame_domains: ["https://trusted-embed.com"],
    redirect_domains: ["https://oauth.provider.com"],
  },
};

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Field Reference

MCP Apps (camelCase)Apps SDK (snake_case)Description
connectDomainsconnect_domainsDomains for fetch, XHR, WebSocket
resourceDomainsresource_domainsDomains for scripts, styles, images
baseUriDomainsbase_uri_domainsDomains for base URI (MCP Apps)
frameDomainsframe_domainsDomains for iframe embeds
redirectDomainsredirect_domainsDomains for redirects (ChatGPT-specific)
scriptDirectivesscript_directivesCustom script CSP directives, not all clients support this (e.g. ChatGPT)
styleDirectivesstyle_directivesCustom style CSP directives
Your CSP domains are merged with your server’s base URL automatically. For ChatGPT, OpenAI’s required domains (*.oaistatic.com, etc.) are also added. For MCP Apps clients, only the domains you declare are used.

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Environment Variables

# Base URL — auto-included in widget CSP
MCP_URL=https://myserver.com

# Additional domains (comma-separated) — appended to widget CSP
CSP_URLS=https://api.example.com,https://cdn.example.com
  • MCP_URL: Base URL for widget assets and public files. Also used by the server to configure CSP.
  • CSP_URLS: (Optional) Additional domains to whitelist. Supports comma-separated list. Required for static deployments where widget assets are served from different domains.

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Static Deployments

When widgets are served from static storage (e.g., Supabase Storage) while the MCP server runs elsewhere, set:
  • MCP_URL: Where widget assets are stored
  • MCP_SERVER_URL: Where the MCP server runs (for API calls)
  • CSP_URLS: Domains for storage and API access (e.g., https://YOUR_PROJECT.supabase.co)
See Supabase deployment for a complete setup.
Alternative: Instead of the global CSP_URLS environment variable, configure CSP per-widget in metadata.csp

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Inspector Debugging

The mcp-use Inspector provides a CSP Mode Toggle for testing:
  • Permissive — Relaxed CSP for debugging
  • Widget-Declared — Enforces the widget’s declared CSP (production-like)
CSP violations are logged in the console. Use Widget-Declared mode to catch CSP issues before production deployment.
See Debugging ChatGPT Apps for details.

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Next Steps