AI Firewall for LLM Apps — Block Prompt Injection & Redact PII with Industry-Leading Accuracy

FilterPrompt is the AI firewall that protects LLM applications from prompt injection, jailbreaks, PII leakage, and policy violations. Drop in our proxy and inspect every prompt and response across OpenAI, Anthropic, Google Gemini, Azure OpenAI, and any OpenAI-compatible endpoint — with 99%+ detection accuracy, per-tenant rules, and full audit logs.

What is an AI firewall?

An AI firewall is a security layer that sits between your application and a large language model. Unlike traditional WAFs that inspect HTTP, an AI firewall understands prompts, tool calls, system messages, and model responses. It detects prompt injection, redacts personally identifiable information, blocks jailbreaks, and enforces compliance policy in real time — before any unsafe traffic reaches the model or your users. FilterPrompt implements this as a drop-in proxy you put in front of OpenAI, Anthropic, Gemini, Azure OpenAI, or any OpenAI-compatible endpoint.

Why teams choose FilterPrompt

• Prompt injection protection. Detect direct, indirect, and tool-call injection with patterns, ML detectors, canary tokens, and OWASP LLM Top 10 mapped rules.
• PII & DLP redaction. Block or mask emails, phone numbers, credit cards, government IDs, secrets, API keys, and custom regex — both inbound and outbound.
• Multi-tenant AI gateway. One proxy, many isolated tenants, each with their own provider keys, rules, quotas, rate limits, and audit logs.
• Provider-agnostic. Works with OpenAI, Anthropic Claude, Google Gemini, Azure OpenAI, Mistral, and any OpenAI-compatible endpoint.
• 99%+ detection accuracy. A hybrid pattern + ML engine returns allow / block / redact / warn for every request without breaking the user experience.
• Built-in audit log. Every prompt, response, rule hit, and verdict is recorded — exportable for SOC 2, ISO 27001, HIPAA, and GDPR audits.
• Bring your own keys. Tenants connect their own provider credentials so you never proxy spend or hold secrets you do not need.
• No SDK rewrite. Change one base URL and add an x-firewall-key header. The OpenAI, Anthropic, and Gemini SDKs continue to work unchanged.

How FilterPrompt works

Every request flows through the Prompt Filter Engine, a multi-layer detection pipeline that scores each prompt and response across pattern matching, semantic similarity, machine-learning classifiers, canary tokens, and per-tenant custom rules. The layers run in parallel with short-circuit logic so a clear malicious prompt is blocked in milliseconds, while ambiguous requests get the full ensemble vote. The firewall returns a single verdict — pass, redact, warn, or block — together with an evidence trail you can review in the audit log or export to your SIEM.

How FilterPrompt compares

FilterPrompt focuses on developer-friendly LLM security with bring-your-own-keys, per-tenant rules, transparent verdicts, and a rule engine you can read, fork, and extend. Compare FilterPrompt side-by-side with Lakera Guard, Cloudflare Firewall for AI, PromptShield, Akamai Firewall for AI, and F5 Prompt Security to see exactly where each product fits and where FilterPrompt's multi-tenant model and audit transparency win.

Solution pages

• What is an AI firewall? — category overview, architecture, and threat model.
• Prompt injection protection — direct, indirect, and tool-call injection defenses.
• LLM PII redaction & DLP — inbound and outbound data loss prevention for LLMs.
• Multi-tenant AI gateway — for SaaS platforms and resellers shipping LLM features to many customers.
• OWASP LLM Top 10 coverage — every risk mapped to a FilterPrompt control.
• AI firewall comparison — FilterPrompt vs Lakera, Cloudflare, PromptShield, Akamai, F5.

From the FilterPrompt blog

• Prompt Injection 101: Direct, Indirect & How to Defend
• PII & DLP for LLMs: A Practical Redaction Playbook
• Designing a Multi-Tenant AI Gateway
• From Zero to Secured GPT in 10 Minutes
• Inside the Prompt Filter Engine — Layered Detection Explained
• OWASP LLM Top 10 — Mapped to Firewall Rules
• Prompt Firewall Tutorial: Build Production LLM Security in One Afternoon
• How to Implement an LLM Firewall: A Step-by-Step Guide
• Prompt Injection Prevention Techniques That Actually Work in 2025
• AI Firewall Comparison Guide: How to Choose the Right LLM Security Vendor
• Best Practices for LLM Security: A 30-Item Checklist for Production GenAI
• Free LLM Security Tools: An Honest 2025 Roundup
• Open Source Prompt Firewall Options: What Exists, What Works, What Is Missing
• Prompt Firewall vs AI Gateway: What Is the Difference and Which Do You Need?
• AI Firewall for Startups: Ship LLM Features Without Hiring a Security Team
• The 2025 LLM Security Checklist Every Engineering Lead Should Print
• Lakera vs Cloudflare Firewall for AI vs FilterPrompt: Honest 2025 Comparison
• LLM Firewall for RAG Applications: Stopping Indirect Prompt Injection at the Source

Frequently asked questions

What is an AI firewall?

An AI firewall is a security layer that inspects prompts and LLM responses in real time to block prompt injection, redact PII, stop jailbreaks, and enforce per-tenant policy. FilterPrompt is an AI firewall built specifically for LLM applications.

How does FilterPrompt block prompt injection?

FilterPrompt combines pattern matching, ML detectors, canary tokens, semantic similarity, and OWASP LLM Top 10 mapped rules to detect direct, indirect, and tool-call prompt injection with industry-leading accuracy.

Does FilterPrompt redact PII?

Yes. FilterPrompt detects and redacts emails, phone numbers, credit cards, government IDs, secrets, API keys, and custom regex in both prompts and responses, on the way in and out of the model.

Which LLM providers are supported?

OpenAI, Anthropic Claude, Google Gemini, Azure OpenAI, Mistral, and any OpenAI-compatible endpoint. Each tenant brings its own provider keys.

Is FilterPrompt free to try?

Yes — sign up for free, get 10,000 starter requests, and protect your first LLM app in minutes. No credit card required.

Can I self-host FilterPrompt?

FilterPrompt is offered as a managed proxy today. Self-hosted and VPC-isolated deployments are available for enterprise plans on request.

Does FilterPrompt log my prompts?

FilterPrompt records a per-request audit log so you can review every verdict. Logging is per-tenant and you control retention. Sensitive content is redacted from logs by the same rules that protect your users.

Start free — protect your first LLM app