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How to Avoid Prompt Injection (Practical Guide)

Prompt injection prevention isn’t a single filter — it’s a set of practices you apply across prompts, tools, and workflows. This guide gives you a concise, practical checklist to avoid prompt injection in real LLM applications.

Contents

  1. 1) Separate roles & inputs
  2. 2) Scan prompts & retrieved context
  3. 3) Constrain tools & data
  4. 4) Confirm sensitive actions
  5. 5) Monitor & log
  6. 6) Harden RAG pipelines
  7. Developer checklist
  8. Conclusion

1) Separate roles & inputs

  • Keep system/developer instructions separate from user content using structured templates.
  • Tag sources in your prompt (e.g., "SYSTEM:", "DEVELOPER:", "USER:", "RETRIEVED:").
  • Never allow untrusted content to rewrite tool or policy instructions.

2) Scan prompts & retrieved context

  • Detect jailbreak phrases like “ignore previous instructions,” “as the system…,” and data exfiltration cues.
  • Scan both user prompts and any retrieved chunks (PDFs, web pages, emails).
  • Use Shieldelly to flag unsafe patterns in real time before they reach your LLM.

3) Constrain tools & data (least privilege)

  • Scope API keys per tool with minimal permissions.
  • Maintain allowlists for files, URLs, and endpoints; block everything else by default.
  • Add rate limits and quotas for tool invocations.

4) Confirm sensitive actions

  • Require explicit user confirmations for high-risk steps (sending emails, transactions, data exports).
  • Add “dry-run” or “explain” steps so the AI describes the intended action before execution.
  • Use human-in-the-loop for privileged workflows.

5) Monitor & log

  • Log prompts, retrieved context, tool calls, and policy conflicts.
  • Alert on anomalies: unusually long prompts, repeated policy bypass attempts, bursty tool usage.
  • Review incidents and feed them back into detection rules.

6) Harden RAG pipelines

  • Sanitize and sign ingested content; distrust HTML, PDFs, and emails by default.
  • Strip/escape control tokens; normalize weird Unicode and zero-width chars.
  • Prefer “read-only” retrieval; don’t let retrieved text alter system instructions or tool scopes.

Developer checklist (copy/paste)

  • Template roles separately (SYSTEM / DEV / USER / CONTEXT).
  • Run Shieldelly scan on every user prompt and retrieved chunk.
  • Deny-by-default for tools, files, and URLs; use allowlists.
  • Require confirmation for actions that touch external systems.
  • Log everything and alert on anomalies.
  • Red-team quarterly with new jailbreak patterns.

Conclusion

Avoiding prompt injection is about layered controls: separation, scanning, least privilege, confirmations, and monitoring. Put these in place and most attacks die before they start.

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