MCP server for Antigravity: add Sume in mcp_config.json

Google Antigravity supports MCP in Antigravity 2.0, the Antigravity CLI, and the Antigravity IDE. To add a custom server such as Sume's, put it under mcpServers in mcp_config.json, globally at ~/.gemini/config/mcp_config.json or in a workspace at .agents/mcp_config.json, with "serverUrl": "https://mcp.sume.com/mcp". Remote servers must use serverUrl; Antigravity does not support url or httpUrl. Leave out headers and Antigravity handles OAuth itself, through the dynamic client registration Sume's server currently offers; or send your Sume API key in headers.

Antigravity's side comes from its MCP docs; Sume's from MCP quickstart, OAuth and API keys, and MCP tools and gates, all read on 2026-09-27, plus current server code where noted. Sume has no official Antigravity integration: this is a plain remote MCP connection. Sume's basics page says hosted MCP still works but is not the primary integration path today.

How do I add Sume to mcp_config.json?

In the Antigravity IDE, click … at the top of the agent side panel, select MCP Servers, then Manage MCP Servers and View raw config. In the Antigravity CLI, edit the file directly; typing /mcp opens the MCP Manager, which shows each server's status and reloads configurations. Antigravity 2.0 lists servers under Settings, Customizations, Installed MCP Servers. All three use the same mcpServers format:

{
  "mcpServers": {
    "sume": {
      "serverUrl": "https://mcp.sume.com/mcp"
    }
  }
}

How do I sign in to Sume with OAuth?

Antigravity handles OAuth for servers that support dynamic client registration, and Sume's server currently advertises it, so the entry needs no oauth block:

• Open Agent Settings (Cmd+, on Mac, Ctrl+, on Windows or Linux), go to the Customizations tab, and click Authenticate next to the server.
• Sign in on Sume's consent page. Read is locked on and Write is off by default; turn Write on only if the agent should run paid tools, which a read-only session refuses with insufficient_scope.
• Copy the authorization code from the browser, paste it into the settings panel, and click Submit. The server reconnects.
• Antigravity stores tokens in ~/.gemini/antigravity/mcp_oauth_tokens.json and says expired tokens are refreshed automatically. In current code, Sume issues no refresh token and a token lasts one hour, so expect to authenticate again.

How do I use an API key instead?

Add a headers object; Sume accepts Authorization: Bearer or x-api-key, and an API-key session sees the full hosted tool set, write and paid tools included. Antigravity's MCP page shows header values written directly into the file, so put this entry in the global file rather than a workspace's .agents/mcp_config.json, and keep it out of version control. Sume's docs say to keep keys on trusted servers, CI secret stores, or local developer machines.

{
  "mcpServers": {
    "sume": {
      "serverUrl": "https://mcp.sume.com/mcp",
      "headers": { "Authorization": "Bearer <SUME_API_KEY>" }
    }
  }
}

How do I keep paid Sume tools behind an approval?

Antigravity runs unconfigured MCP tools in Ask mode, which requires your approval before a tool runs. Allow rules match mcp(server/tool), mcp(server/*), or mcp(*): allowing a read tool such as mcp(sume/tools_list) is fine, but mcp(sume/*) or mcp(*) would let paid tools run without asking. Sume's own gates still apply: paid calls need an idempotency_key, dry_run=true previews admission and cost without submitting, and max_spend_usd caps a call only when you pass it.

Can I reuse a Gemini CLI config?

Not as written. Gemini CLI reads MCP servers from settings.json and uses httpUrl for a streaming HTTP endpoint, a key Antigravity does not support for remote servers, so copy the URL into serverUrl in mcp_config.json instead. Gemini CLI MCP server covers that client. Once connected, ask the agent to call mcp_health, then tools_list, which lists every tool the session can see; Sume MCP tools list groups them by read, write, and paid.