mcp-chrome HTTP 400 error: working MCP config for Claude Code, Gemini CLI, Cursor

Question

I'm using hangwin/mcp-chrome and connecting to http://127.0.0.1:12306/mcp from MCP clients, but the server returns an HTTP 400 error. The reporter who debugged this says a 400 is usually caused by a wrong client-side configuration. What are the exact working configurations for Claude Code, Gemini CLI, and Cursor?

Originally asked on GitHub: https://github.com/hangwin/mcp-chrome/issues/103

AgentArmorHQ team · Accepted Answer

The issue is still open, but the reporter debugged the HTTP 400 and concluded it is almost always caused by an incorrect client-side MCP configuration. The configurations below were posted in the thread and are the working setup to use.

**Claude Code** (run in a terminal):
```
claude mcp add -s user --transport http chrome-mcp-server http://127.0.0.1:12306/mcp
```

**Gemini CLI**:
```json
{
  "mcpServers": {
    "chrome-mcp-server": {
      "httpUrl": "http://127.0.0.1:12306/mcp",
      "timeout": 5000
    }
  }
}
```

**Cursor**:
```json
{
  "mcpServers": {
    "chrome-mcp-server": {
      "url": "http://127.0.0.1:12306/mcp"
    }
  }
}
```

Note that the field name differs per client: `httpUrl` for Gemini CLI, `url` for Cursor, and Claude Code uses the `--transport http` flag in the CLI command. One commenter replied that this worked, and another confirmed the config can be used with gemini-cli. As general advice, make sure the mcp-chrome server is actually running and listening on port 12306 before testing.

AgentArmorHQ team · Answer

**What a GitHub user tried on GitHub** (Worked)

The reporter debugged the 400 error and posted working configurations: Claude Code via `claude mcp add -s user --transport http chrome-mcp-server http://127.0.0.1:12306/mcp`, Gemini CLI with the `httpUrl` field and `timeout: 5000`, and Cursor with the `url` field.

Source: https://github.com/hangwin/mcp-chrome/issues/103

AgentArmorHQ team · Answer

**What @realpeterz tried on GitHub** (Worked)

A commenter applied the posted configuration and replied "This worked. Thanks!"

Source: https://github.com/hangwin/mcp-chrome/issues/103#issuecomment-3215655720

AgentArmorHQ team · Answer

**What @hongdartw tried on GitHub** (Worked)

A commenter stated the posted config can be used in gemini-cli.

Source: https://github.com/hangwin/mcp-chrome/issues/103#issuecomment-3356194105

mcp-chrome HTTP 400 error: working MCP config for Claude Code, Gemini CLI, Cursor

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