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Owada Tomohiro
Owada Tomohiro

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I Rewrote Google's Gemini CLI in Go - 68x Faster Startup

#cli #gemini #go #performance

TL;DR

  • Google's official Gemini CLI has ~1 second Node.js startup overhead
  • I rewrote it in Go → startup is now 0.01 seconds (68x faster)
  • Reuses auth from official CLI, so your free tier / Workspace quota just works

https://github.com/tomohiro-owada/gmn

Why I Built This

Google's official Gemini CLI is an amazing tool. Rich TUI, seamless Google authentication, excellent MCP support. I loved using it.

But there was one issue for my use case: startup time.

$ time gemini --version
0.22.2
gemini --version  1.00s user 0.24s system 129% cpu 0.951 total
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~1 second just to start. That's the Node.js runtime overhead. Fine for interactive use, but painful when you're calling it repeatedly in shell scripts.

The Solution: gmn

So I rewrote the core functionality in Go. The result is gmn (short for gemini-mini):

$ time gmn --version
gmn version 0.2.0
gmn --version  0.00s user 0.00s system 47% cpu 0.014 total
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0.014 seconds. 68x faster.

Benchmarks

Metric gmn Official CLI Improvement
Startup 0.01s 0.95s 68x
Binary 5.6MB ~200MB 35x
Runtime None Node.js -

With API response time included:

$ time gmn "hi"
Hello! How can I help you today?
gmn "hi"  0.01s user 0.02s system 0% cpu 3.205 total

$ time gemini -p "hi"
I'm ready to help. What would you like to do?
gemini -p "hi"  2.13s user 0.53s system 24% cpu 10.933 total
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Installation

Prerequisites (Important!)

gmn doesn't have its own authentication. You must authenticate once with the official Gemini CLI first:

npm install -g @google/gemini-cli
gemini  # Choose "Login with Google"
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gmn reuses credentials from ~/.gemini/. Your free tier quota or Workspace Code Assist quota applies.

Install gmn

Homebrew:

brew install tomohiro-owada/tap/gmn
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Go:

go install github.com/tomohiro-owada/gmn@latest
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Binary:
Download from Releases

Usage 

# Simple prompt
gmn "Explain quantum computing"

# With file context
gmn "Review this code" -f main.go

# Pipe input
cat error.log | gmn "What's wrong?"

# JSON output
gmn "List 3 colors" -o json

# Different model
gmn "Write a poem" -m gemini-2.5-pro
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Technical Details

Discovering the API

Initially, I tried using generativelanguage.googleapis.com (the public Gemini API), but got 403 errors due to OAuth scope mismatch.

Reading the official CLI source code, I discovered it actually uses the Code Assist API (cloudcode-pa.googleapis.com). This is an internal Google Cloud API, not publicly documented.

Auth Reuse

The official CLI stores OAuth tokens in ~/.gemini/oauth_creds.json. gmn reads this file and refreshes tokens when needed:

if creds.IsExpired() {
    creds, err = authMgr.RefreshToken(creds)
}
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MCP Support

gmn also supports MCP (Model Context Protocol). It reads the same ~/.gemini/settings.json config:

gmn mcp list
gmn mcp call my-server tool-name arg=value
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What's NOT Included

gmn is focused on non-interactive use cases:

  • Interactive/TUI mode → use official CLI
  • OAuth flow → authenticate with official CLI first
  • API Key / Vertex AI auth

Conclusion

This is a love letter to Google's official Gemini CLI. I just needed something faster for scripting.

If you use Gemini in shell scripts or automation, give gmn a try:

brew install tomohiro-owada/tap/gmn
gmn "Hello, World!"
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https://github.com/tomohiro-owada/gmn

Acknowledgments

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