MCP Inspector Apps panel white screen: ENOENT sandbox_proxy.html in server/static
MCP Inspector v0.20.0 on Debian 13 (Chromium 144 and Firefox 140) shows a white screen in the Apps panel instead of rendering the app, with this error: MCP Apps sandbox not loaded: Error: ENOENT: no such file or directory, open '.../node_modules/@modelcontextprotocol/inspector/server/static/sandbox_proxy.html'. The file exists only under server/build/static, not server/static. Is there a fix or a workaround?
Originally asked on GitHub: https://github.com/modelcontextprotocol/inspector/issues/1082
6 answers
Fixed for npx installs in the v1 source by PR #1113, though the thread names no released version with the fix; the issue was later closed as NOT_PLANNED because v1 is deprecated and only receives security fixes. A commenter also reported that the Docker image still showed the same problem after that PR, with the path /app/server/static/sandbox_proxy.html, and a separate PR #1736 was submitted but its merge status is not stated in the thread.
Working workaround from the thread for the npx case:
d=$(find ~/.npm/_npx -type d -path "*/node_modules/@modelcontextprotocol/inspector/server") mkdir "$d/static" cp "$d/build/static/sandbox_proxy.html" "$d/static/"
A later commenter confirmed this copy-based workaround fixed the Apps panel. The original reporter also got the app to render by symlinking the expected server/static path to the existing server/build/static path. If you still hit the error in v2, the maintainers asked for a fresh issue against v2 with reproduction steps, since v1 is closed to non-security changes.
Did this work for you?What @rafaeljusto tried on GitHub (Worked)
Suggested copying sandbox_proxy.html from build/static into a new static directory under the npx-installed inspector server folder; another commenter later confirmed it worked.
Did this work for you?What a GitHub user tried on GitHub (Worked)
Reporter symlinked the expected server/static path to the existing server/build/static path and the MCP app rendered.
Source: https://github.com/modelcontextprotocol/inspector/issues/1082 (opens external site)
Did this work for you?What @jwoods02 tried on GitHub (Partly worked)
Contributor said the bug was fixed by PR #1113 for the npx case, but did not mention a released version.
Did this work for you?What @SteveTalbot tried on GitHub (Didn't work)
After PR #1113, a commenter reported the same ENOENT in the Docker container, with the path /app/server/static/sandbox_proxy.html.
Did this work for you?What @safe049 tried on GitHub (Outcome unclear)
A user submitted PR #1736 saying it fixes the bug; the thread does not confirm whether it was merged or released.
Did this work for you?
Related questions
- MCP Inspector 0.10.2 sends null for unset optional params (error -32602)?
- Why does npx @modelcontextprotocol/inspector fail with 'mcp-inspector: command not found' after 0.10.0?
- How do I increase MCP Inspector's 10-second request timeout?
- MCP Inspector crashes with 'Controller is already closed' on fastmcp Streamable HTTP
- Why does the MCP Inspector Docker container refuse connections on localhost:6274, and how do I fix it?