How do I pass an Authorization header to MCP Inspector in CLI mode?

Question

MCP Inspector's UI mode lets you set an Authorization header for a remote SSE URL, but the mcp config file used in CLI mode has no way to define HTTP headers. I need to pass a bearer token to a remote HTTP MCP server when launching the inspector from the command line. Was this feature added, and if so, what is the correct config format?

Originally asked on GitHub: https://github.com/modelcontextprotocol/inspector/issues/420

AgentArmor team · Accepted Answer

This feature request was closed as completed: a contributor implemented custom header support for CLI mode in PR #716 (modelcontextprotocol/inspector#716), after the original request in May 2025.

What the thread itself establishes:
- UI mode already supported setting an Authorization header for remote SSE URLs; CLI mode did not at the time of the request.
- The requested configuration was a headers block inside the mcpServers entry of the mcp config file, alongside the server URL:

```json
{
  "mcpServers": {
    "my_mcp_server": {
      "url": "https://mcp.example.com/sse",
      "headers": {
        "Authentication": "<my-token-here>"
      }
    }
  }
}
```

Note the example in the original issue used array syntax (`"headers": ["Authentication": ...]`), which is not valid JSON; a headers object of name/value pairs is the format to ask for.

General advice: the thread only links the PR and does not show the final merged config syntax or release notes, so check PR #716 or the current MCP Inspector README for the exact header key names and any CLI flags before relying on this. As general security practice, avoid hard-coding bearer tokens in a committed mcp config file — use an environment variable or a secret manager if the implementation supports it.

How do I pass an Authorization header to MCP Inspector in CLI mode?

1 answer