gemini-cli-rs

English | 日本語

Gemini CLI written in Rust, optimized for use as an MCP tool in Claude Code.

Features

• MCP Server mode — Runs as a native MCP server (--mcp-server); integrates directly with Claude Code
• SSE Streaming — Streams responses from the Gemini API in real time
• Google Search Grounding — Always-on; sources are printed to stderr in CLI mode and included in the response in MCP mode
• GEMINI.md Context — Loads project-specific context from GEMINI.md (walks up to the nearest .git root)
• Single-shot mode — Designed for non-interactive, scriptable use

Prerequisites

• A Gemini API key (GEMINI_API_KEY) — get one at Google AI Studio

Installation

Download pre-built binary

Pre-built binaries are available for macOS and Linux on the Releases page.

# Apple Silicon macOS
curl -L https://github.com/heki1224/gemini-cli-rs/releases/latest/download/gemini-cli-rs-aarch64-apple-darwin.tar.xz | tar -xJ
mv gemini ~/.local/bin/gemini

# Intel macOS
curl -L https://github.com/heki1224/gemini-cli-rs/releases/latest/download/gemini-cli-rs-x86_64-apple-darwin.tar.xz | tar -xJ
mv gemini ~/.local/bin/gemini

# Linux x86_64
curl -L https://github.com/heki1224/gemini-cli-rs/releases/latest/download/gemini-cli-rs-x86_64-unknown-linux-gnu.tar.xz | tar -xJ
mv gemini ~/.local/bin/gemini

Build from source

git clone https://github.com/heki1224/gemini-cli-rs
cd gemini-cli-rs
cargo build --release
cp target/release/gemini ~/.local/bin/gemini

Usage

CLI mode

# Set your API key
export GEMINI_API_KEY="your-api-key"

# Send a prompt
gemini -p "What is the capital of France?"

# Use a different model
gemini -m gemini-2.5-pro -p "Explain Rust's borrow checker"

Grounding sources are printed to stderr after the response.

MCP server mode

In MCP mode the binary is launched automatically by Claude Code — you do not normally run it directly. See MCP Setup for registration steps.

# Manual launch (for debugging)
GEMINI_API_KEY="your-api-key" gemini --mcp-server

Grounding sources are included in the response text (not stderr).

Options

Flag	Description	Default
-p, --prompt	Prompt to send (required in CLI mode)	—
-m, --model	Model to use	gemini-3-flash-preview
--mcp-server	Run as MCP server (JSON-RPC 2.0 over stdio)	—

The API key is read from the GEMINI_API_KEY environment variable only (no --api-key flag).

Environment variables

Variable	Description	Default
GEMINI_API_KEY	Gemini API key (required)	—
GEMINI_DEFAULT_MODEL	Override the default model at runtime	gemini-3-flash-preview
GEMINI_HIGH_PERF_MODEL	Override the high-performance model at runtime	gemini-3.1-pro-preview

MCP Setup (Claude Code)

This tool is designed to be used as an MCP server inside Claude Code, providing Gemini with Google Search Grounding as a secondary AI assistant.

1. Build the binary

cargo build --release

2. Register as an MCP server

claude mcp add gemini /path/to/target/release/gemini --scope user -- --mcp-server

Use --scope user to make it available across all projects, or --scope project to limit it to the current project.

3. Set your API key

Add GEMINI_API_KEY to your shell profile (~/.zshrc, ~/.bashrc, etc.):

export GEMINI_API_KEY="your-api-key"

4. Restart Claude Code and verify

claude mcp list

Once registered, the ask_gemini_mcp tool is available. Claude Code routes prompts to Gemini with real-time Google Search grounding.

MCP tool parameters

Parameter	Type	Description
prompt	string (required)	The prompt to send to Gemini. Aliases request, query, message, text, input are also accepted as fallbacks
model	string	Override the model for this request (ignored when thinking=true)
thinking	boolean	Use the high-performance model (gemini-3.1-pro-preview) for complex reasoning or deep analysis. Default: false

Note: The binary writes protocol messages to stdout and all logs to stderr. Do not redirect stderr if you want to see debug output.

GEMINI.md

Place a GEMINI.md file in your current working directory (or any parent directory) to inject system-level context into every request. The search walks up to the nearest .git directory; if no .git is found, it continues to the filesystem root. Useful for project-specific instructions.

Note: Files larger than 1 MB are silently ignored.

your-project/
├── .git/
├── GEMINI.md   ← loaded automatically
└── src/

License

MIT — see LICENSE