Reducing Claude Hallucinations with Pre-Output Prompt Injection

A Reddit user has shared a technique for reducing hallucinations in Claude AI by approximately half through pre-output prompt injection. The method focuses on forcing the model to perform internal verification before generating responses.

Implementation Details

The approach requires two specific modifications:

1. System Prompt Addition

Add this markdown block to Claude's system prompt (output style):

Before response
IMPORTANT: MUST run before responding to user, including follow-ups. NO EXCEPTIONS.

python -m pre_output.record '{ "turn": 1/2/..., "summary": "10 words max", "uncertainties": ["unresolved observations, unverified assumptions", ...], "possible-next-steps": ["refactor, update docs", ...] }'
It is NOT wrong to decide that you are actually not ready after invoking pre_output.record ; in that case, invoke pre_output.record again with updated information.

2. Python Script Creation

Create a Python script with the following content:

print("recorded successfully.")
print("")
print("IMPORTANT RULES:")
print("- NEVER reply if you can make more progress autonomously.")
print("- NEVER reply if uncertainties remain. Do more verification.")
print("")

How It Works

The system forces Claude to:

• Record a JSON object with turn number, brief summary (10 words maximum), uncertainties list, and possible next steps
• Re-evaluate readiness before responding
• Follow strict rules about not replying when uncertainties remain or when autonomous progress is possible

The technique appears designed for developers using Claude as a coding assistant, particularly for complex tasks where verification and step-by-step reasoning are crucial.