Antigravity CLI

Antigravity CLI (agy) is the command-line companion to Google Antigravity, a Gemini-based agent. Unlike the Antigravity IDE, agy has a native plugin system (agy plugin install) and a hook surface, so context-mode ships as a first-class agy plugin. A single command registers the MCP server, a routing rule, a routing skill, and bounded PreToolUse/PostToolUse/Stop hooks that steer data-heavy tool output into the sandbox — the model writes a program that processes the data and prints only the answer.

Install

The plugin install is a single agy command, but the plugin's MCP server and hooks run the global context-mode binary, so npm install -g context-mode is a prerequisite.

npm install -g context-mode

agy plugin install https://github.com/mksglu/context-mode/tree/main/configs/antigravity-cli

context-mode hook antigravity-cli pretooluse
context-mode hook antigravity-cli posttooluse
context-mode hook antigravity-cli stop

Hook scope

context-mode wires only the surfaces that have a verified mapping on agy:

Where agy reads its config

agy shares the ~/.gemini/ session root with the rest of the Gemini family; the session database is keyed by project hash to prevent collisions. The relevant paths:

The plugin install registers everything under its plugin profile rather than the global MCP and hooks files.

Alternative (MCP only, no plugin)

If you cannot use the plugin install, register the MCP server manually by adding context-mode to ~/.gemini/config/mcp_config.json under mcpServers. This path ships no hooks, so routing enforcement is advisory only.

{
  "mcpServers": {
    "context-mode": {
      "command": "context-mode",
      "env": {
        "CONTEXT_MODE_PLATFORM": "antigravity-cli"
      }
    }
  }
}

agy is also detected automatically through the MCP handshake (clientInfo.name of agy / antigravity-cli) and config-dir markers, so the CONTEXT_MODE_PLATFORM env above is a belt-and-suspenders override rather than a strict requirement — it pins detection when another host like Claude Code is co-installed.

Verify your savings

Confirm context-mode is actually saving you tokens, not just that the tools respond.

• In an agy session, type ctx stats in chat to see the tokens saved and the savings ratio for the session — or run any prompt and re-check after a few data-heavy operations.
• Run context-mode doctor to confirm the hooks and MCP server are registered.

context-mode doctor

context-mode doctor checks:

• Language runtimes
• The FTS5 knowledge base
• MCP registration
• The PreToolUse/PostToolUse (best-effort Stop) hooks, across both the plugin profile (~/.gemini/config/plugins/context-mode/) and the global manual profile

When degraded, it prints agy plugin install ... or context-mode upgrade as the repair fix. A clean run means the MCP server is reachable and the hooks are wired.

Related