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
-
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)
-
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)
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 |
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 |
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
- Be specific: Provide clear, structured prompts for what to analyze
- Use include-directories: Explicitly specify all relevant directories
- 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
- Leverage Gemini 3's strengths: 35% better at software engineering tasks, exceptional at agentic workflows and vibe coding
- Break down complex tasks: Even with large context, structured analysis is more effective
- 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