Replyz / Gemini CLI and Antigravity

How to add an MCP server to Gemini CLI and Antigravity CLI.

Both read MCP servers from a JSON file under ~/.gemini, but with different file names and fields. This page shows each one for a remote server with an API key, using the Replyz MCP server as the example. With it, the agent gets an email inbox of its own.

Get early access The Replyz MCP server

Gemini CLI or Antigravity CLI?

Gemini CLI's documentation says it was replaced by Antigravity CLI on 18 June 2026. If you installed it after that date, follow the Antigravity section. The two use different config files and different field names, so a Gemini CLI config won't work as-is in Antigravity.

How do you add an MCP server to Gemini CLI?

With a command

gemini mcp add --transport http \
  --header "Authorization: Bearer $REPLYZ_API_KEY" \
  replyz https://mcp.replyz.io/mcp

By default this writes to the project's .gemini/settings.json. Add -s user to make it global.

In settings.json

Global: ~/.gemini/settings.json. Project: .gemini/settings.json.

{
  "mcpServers": {
    "replyz": {
      "httpUrl": "https://mcp.replyz.io/mcp",
      "headers": {
        "Authorization": "Bearer YOUR_REPLYZ_API_KEY"
      }
    }
  }
}

Use httpUrl for Streamable HTTP; url is for SSE. The docs only describe environment-variable expansion for the env block, not for headers, so keep this file out of version control.

Check it

gemini mcp list

Or type /mcp in a session to see each server's status and tools.

How do you add an MCP server to Antigravity CLI?

Global: ~/.gemini/config/mcp_config.json. Workspace: .agents/mcp_config.json. The same files are used by the Antigravity IDE.

{
  "mcpServers": {
    "replyz": {
      "serverUrl": "https://mcp.replyz.io/mcp",
      "headers": {
        "Authorization": "Bearer YOUR_REPLYZ_API_KEY"
      }
    }
  }
}

Antigravity uses serverUrl (or url) and only supports Streamable HTTP for remote servers; httpUrl isn't supported. Type /mcp in the CLI to open the MCP manager, check the status and reload.

What can the agent do with its own inbox?

Test sign-up flows

Read codes and links

get_verification returns the code or link from the right email.

Sign up for services

Create accounts with the agent's own address, not yours.

Report back by email

email_my_human writes to you when it needs a decision.

Full tool list on the MCP server page. Other agents: all agents.

Frequently asked questions

How do I add a remote MCP server to Gemini CLI?

Add it to mcpServers in ~/.gemini/settings.json with httpUrl and a headers object, or run gemini mcp add --transport http --header "Authorization: Bearer <key>" <name> <url>.

Should I use url or httpUrl in Gemini CLI?

httpUrl, for Streamable HTTP servers. In Gemini CLI, url is for SSE endpoints.

Is Gemini CLI still maintained?

Its documentation says Gemini CLI was replaced by Antigravity CLI on 18 June 2026. Antigravity CLI reads MCP servers from ~/.gemini/config/mcp_config.json and uses serverUrl instead of httpUrl.

How do I add a remote MCP server to Antigravity CLI?

Add it to mcpServers in ~/.gemini/config/mcp_config.json (or .agents/mcp_config.json in a workspace) with serverUrl and headers, then run /mcp to check its status.

How do I check that the server is connected?

In Gemini CLI, run gemini mcp list or /mcp in a session. In Antigravity CLI, type /mcp to open the MCP manager.