Use --system-prompt to Give Claude a One-Off Persona Without Changing CLAUDE.md

Sometimes you want Claude to approach a task with a specific mindset — as a security auditor, a performance expert, or a strict reviewer — without permanently changing your project configuration. The --system-prompt flag lets you inject a one-off instruction.

claude --system-prompt "You are a senior security engineer. 
Approach every task with a security-first mindset. Flag any 
code that handles user input, authentication, or sensitive data."

Claude adopts the persona for this session only. Your CLAUDE.md stays untouched, and the next session returns to normal.

This is especially useful for specialized tasks:

# Security review mode
claude --system-prompt "Act as a penetration tester. Assume every 
input is malicious. Find every way to exploit this code."

# Performance optimization mode
claude --system-prompt "You are a performance engineer. Every 
suggestion must consider memory usage, query count, and response time. 
Measure before and after."

# Strict code review mode
claude --system-prompt "Review code as if it's going into a 
safety-critical system. No shortcuts, no 'good enough'. 
Every edge case must be handled."

# Junior-friendly teaching mode
claude --system-prompt "Explain everything at a beginner level. 
Show the reasoning behind each decision. Include links to 
relevant documentation."

Combine with -p for specialized one-liners:

# Quick security scan with a security-focused system prompt
claude --system-prompt "Focus exclusively on security vulnerabilities" \
  -p "scan src/ for injection vulnerabilities"

# Database-focused analysis
claude --system-prompt "You are a DBA. Optimize for query performance." \
  -p "review all database queries in the order module"

The --system-prompt stacks with your existing CLAUDE.md — both are active during the session. Use it to add temporary focus without removing your project's permanent rules.

CLAUDE.md is for permanent rules. --system-prompt is for temporary mindsets — use it when you need Claude to think differently for one task.

via Claude Code