How to Block Prompt Injection, Base64 Jailbreaks & API Key Leaks Locally in Node.js (Zero Dependencies)

Every week, another AI wrapper or internal RAG tool accidentally leaks a production sk-proj-... key, customer SSN, or database URI to a third-party LLM provider—or gets tricked by a <|im_start|>system delimiter injection.

Most teams either ignore the problem or add a heavy 300ms external guardrail API call on every request.

To solve this locally in <1ms with zero runtime dependencies, I built PromptShield Pro —a local-first LLM Security Firewall, Reversible PII Redactor, Multi-Model Cost Simulator, and 30-Template Production System Prompt Vault.

16+ Credential & PII Formats (with Reversible Redaction): Scans for OpenAI ( sk-proj-... ), Anthropic ( sk-ant-... ), Gemini, AWS ( AKIA... ), GitHub, Stripe, and Slack keys, PostgreSQL/MongoDB connection URIs, JWTs, Luhn-verified credit cards, SSNs, and emails—replacing them with [REDACTED_...] tokens before calling the LLM and restoring them afterward via restoreRedacted().

Multi-Layer Prompt Injection & Obfuscation Firewall: Detects direct instruction overrides, DAN/DevMode personas, system prompt extraction attempts, XML/ChatML delimiter spoofing, markdown image webhook exfiltration, Base64-encoded instructions, and invisible zero-width character steganography.

Deterministic Prompt Compressor & Linter: Strips conversational filler and lints missing JSON schemas or unisolated {{variables}}, saving 15%–35% on input tokens.

Multi-Model Cost & Prompt Caching Simulator: Compares monthly spend and prompt-caching savings across GPT-4o, o3-mini, Claude 3.7 Sonnet, Gemini 2.5 Pro/Flash, DeepSeek V3, and Llama 3.3 70B.

const { scanAndRedact, inspectPromptSecurity, compressPrompt } = require ( './src/index ' ); // 1. Mask API keys, DB URIs, and PII before calling any LLM API const { redactedText, vaultMap } = scanAndRedact ( userPrompt ); // 2. Block Prompt Injections, Delimiter Escapes & Base64 Jailbreaks const security = inspectPromptSecurity ( redactedText ); if ( security. blocked ) { throw new Error ( `Blocked adversarial prompt ( ${ security. riskLevel } )` ); } // 3.

Strip token bloat & wrap in hardened XML data boundary const { compressedText } = compressPrompt ( redactedText ); Enter fullscreen mode Exit fullscreen mode 🚀 Try the Free CLI Starter or Grab the Complete Toolkit I've released a Free Starter Edition ( $0+ ) with the CLI scanner, 5 starter system prompts, and the 30-case Red-Team benchmark suite, alongside the PromptShield Pro Complete Toolkit ( $29 ) which includes the Offline Interactive Web Studio ( studio/index.html ) and all 30 Schema-Enforced Production System Prompts across 6 engineering categories:

👉 Download PromptShield Lite (Free) or PromptShield Pro on Gumroad

Would love any feedback from the community on additional secret formats or adversarial injection patterns you'd like to see added!