Gemini Skill Guide

When to Use Gemini

• WHEN ASKED TO BE ACTIVATED
• Code Review: Comprehensive code reviews across multiple files
• Plan Review: Analyzing architectural plans, technical specifications, or project roadmaps
• Big Context Processing: Tasks requiring >200k tokens of context (entire codebases, documentation sets)
• Multi-file Analysis: Understanding relationships and patterns across many files

⚠️ Critical: Background/Non-Interactive Mode Warning

NEVER use --approval-mode default in background or non-interactive shells (like Claude Code tool calls). It will hang indefinitely waiting for approval prompts that cannot be provided.

For automated/background reviews:

• ✅ Use --approval-mode yolo for fully automated execution
• ✅ OR wrap with timeout: timeout 300 gemini ...
• ❌ NEVER use --approval-mode default without interactive terminal

Symptoms of hung Gemini:

• Process running 20+ minutes with 0% CPU usage
• No network activity
• Process state shows 'S' (sleeping)

Fix hung process:

# Check if hung
ps aux | grep gemini | grep -v grep

# Kill if necessary
pkill -9 -f "gemini.*gemini-3-pro-preview"

Running a Task

1. Ask the user (via AskUserQuestion) which model to use in a single prompt. Available models:

   • gemini-3-pro-preview ⭐ (flagship model, best for coding & complex reasoning, 35% better at software engineering than 2.5 Pro)
   • gemini-3-flash (sub-second latency, distilled from 3 Pro, best for speed-critical tasks)
   • gemini-2.5-pro (legacy option, strong all-around performance)
   • gemini-2.5-flash (legacy option, cost-efficient with thinking capabilities)
   • gemini-2.5-flash-lite (legacy option, fastest processing)

2. Select the approval mode based on the task:

   • default: Prompt for approval (⚠️ ONLY for interactive terminal sessions)
   • auto_edit: Auto-approve edit tools only (for code reviews with suggestions)
   • yolo: Auto-approve all tools (✅ REQUIRED for background/automated tasks)

3. Assemble the command with appropriate options:

   • -m, --model <MODEL> - Model selection
   • --approval-mode <default|auto_edit|yolo> - Control tool approval
   • -y, --yolo - Alternative to --approval-mode yolo
   • -i, --prompt-interactive "prompt" - Execute prompt and continue interactively
   • --include-directories <DIR> - Additional directories to include in workspace
   • -s, --sandbox - Run in sandbox mode for isolation

4. For background/automated tasks, ALWAYS use --approval-mode yolo or add timeout wrapper. NEVER use default in non-interactive shells.

5. Run the command and capture the output. For background/automated mode:

   # Recommended: Use yolo for background tasks
   gemini -m gemini-3-pro-preview --approval-mode yolo "Review this codebase for security issues"
   
   # Or with timeout (5 min limit)
   timeout 300 gemini -m gemini-3-pro-preview --approval-mode yolo "Review this codebase"

6. For interactive sessions with an initial prompt:

   gemini -m gemini-3-pro-preview -i "Review the authentication system" --approval-mode auto_edit

7. After Gemini completes, inform the user: "The Gemini analysis is complete. You can start a new Gemini session for follow-up analysis or continue exploring the findings."

Quick Reference

Use case	Approval mode	Key flags
Background code review	yolo ✅	-m gemini-3-pro-preview --approval-mode yolo
Background analysis	yolo ✅	-m gemini-3-pro-preview --approval-mode yolo
Background with timeout	yolo ✅	timeout 300 gemini -m gemini-3-pro-preview --approval-mode yolo
Interactive code review	default	-m gemini-3-pro-preview --approval-mode default (interactive terminal only)
Code review with auto-edits	auto_edit	-m gemini-3-pro-preview --approval-mode auto_edit
Automated refactoring	yolo	-m gemini-3-pro-preview --approval-mode yolo
Speed-critical background	yolo ✅	-m gemini-3-flash --approval-mode yolo
Cost-optimized background	yolo ✅	-m gemini-2.5-flash --approval-mode yolo
Multi-directory analysis	yolo (if background)	--include-directories <DIR1> --include-directories <DIR2>
Interactive with prompt	auto_edit or default	-i "prompt" --approval-mode <mode>

Model Selection Guide

Model	Best for	Context window	Key features
gemini-3-pro-preview ⭐	Flagship model: Complex reasoning, coding, agentic tasks	1M input / 64k output	Vibe coding, 76.2% SWE-bench, $2-4/M input
gemini-3-flash	Sub-second latency, speed-critical applications	1M input / 64k output	Distilled from 3 Pro, TPU-optimized
gemini-2.5-pro	Legacy: Strong all-around performance	1M input / 65k output	Thinking mode, mature stability
gemini-2.5-flash	Legacy: Cost-efficient, high-volume tasks	1M input / 65k output	Best price ($0.15/M), thinking mode
gemini-2.5-flash-lite	Legacy: Fastest processing, high throughput	1M input / 65k output	Maximum speed, minimal latency

Gemini 3 Advantages: 35% higher accuracy in software engineering, state-of-the-art on SWE-bench (76.2%), GPQA Diamond (91.9%), and WebDev Arena (1487 Elo). Knowledge cutoff: January 2025.

Coming Soon: gemini-3-deep-think for ultra-complex reasoning with enhanced thinking capabilities.

Common Use Cases

Code Review (Background/Automated)

# For background execution (Claude Code, CI/CD, etc.)
gemini -m gemini-3-pro-preview --approval-mode yolo \
  "Perform a comprehensive code review focusing on:
   1. Security vulnerabilities
   2. Performance issues
   3. Code quality and maintainability
   4. Best practices violations"

# With timeout safety (5 minutes)
timeout 300 gemini -m gemini-3-pro-preview --approval-mode yolo \
  "Perform a comprehensive code review..."

Plan Review (Background/Automated)

# For background execution
gemini -m gemini-3-pro-preview --approval-mode yolo \
  "Review this architectural plan for:
   1. Scalability concerns
   2. Missing components
   3. Integration challenges
   4. Alternative approaches"

Big Context Analysis (Background/Automated)

# For background execution
gemini -m gemini-3-pro-preview --approval-mode yolo \
  "Analyze the entire codebase to understand:
   1. Overall architecture
   2. Key patterns and conventions
   3. Potential technical debt
   4. Refactoring opportunities"

Interactive Code Review (Terminal Only)

# ONLY use default mode in interactive terminal
gemini -m gemini-3-pro-preview --approval-mode default \
  "Review the authentication flow for security issues"

Following Up

• Gemini CLI sessions are typically one-shot or interactive. Unlike Codex, there's no built-in resume functionality.
• For follow-up analysis, start a new Gemini session with context from previous findings.
• When proposing follow-up actions, restate the chosen model and approval mode.
• Use AskUserQuestion after each Gemini command to confirm next steps or gather clarifications.

Error Handling

• Stop and report failures whenever gemini --version or a Gemini command exits non-zero.
• Request direction before retrying failed commands.
• Before using high-impact flags (--approval-mode yolo, -y, --sandbox), ask the user for permission using AskUserQuestion unless already granted.
• When output includes warnings or partial results, summarize them and ask how to adjust using AskUserQuestion.

Troubleshooting Hung Gemini Processes

Detection

# Check for hung processes
ps aux | grep -E "gemini.*gemini-3" | grep -v grep

# Look for these symptoms:
# - Process running 20+ minutes
# - CPU usage at 0%
# - Process state 'S' (sleeping)
# - No network connections

Diagnosis

# Get detailed process info
ps -o pid,etime,pcpu,stat,command -p <PID>

# Check network activity
lsof -p <PID> 2>/dev/null | grep -E "(TCP|ESTABLISHED)" | wc -l
# If result is 0, process is hung

Resolution

# Kill hung Gemini processes
pkill -9 -f "gemini.*gemini-3-pro-preview"

# Or kill specific PID
kill -9 <PID>

# Verify cleanup
ps aux | grep gemini | grep -v grep

Prevention

• ALWAYS use --approval-mode yolo for background/automated tasks
• Add timeout wrapper for safety: timeout 300 gemini ...
• Never use --approval-mode default in non-interactive shells
• Monitor first run with ps to ensure process completes

Tips for Large Context Processing

1. Be specific: Provide clear, structured prompts for what to analyze
2. Use include-directories: Explicitly specify all relevant directories
3. Choose the right model:
   • Use gemini-3-pro-preview for complex reasoning, coding tasks, and maximum analysis quality (recommended default)
   • Use gemini-3-flash for speed-critical tasks requiring sub-second response times
   • Use gemini-2.5-flash for cost-optimized high-volume processing
4. Leverage Gemini 3's strengths: 35% better at software engineering tasks, exceptional at agentic workflows and vibe coding
5. Break down complex tasks: Even with large context, structured analysis is more effective
6. Save findings: Ask Gemini to output structured reports that can be saved for reference

CLI Version

Requires Gemini CLI v0.16.0 or later for Gemini 3 model support. Check version: gemini --version