AI Dictionary › Prompting
A prompt firewall is a software layer placed between the user and the language model, dedicated to inspecting, filtering, and possibly blocking suspicious input and output before it reaches the model or the end user. The name deliberately echoes the traditional network firewall: just as the latter controls traffic entering and leaving a network according to predefined rules, a prompt firewall controls the textual traffic entering and leaving an AI system.
Unlike a single safety filter, a prompt firewall is typically a modular system combining multiple detection techniques: known jailbreak and prompt injection patterns, intent classifiers trained to recognize manipulation attempts, consistency checks between the expected and actually received context, and configurable rules specific to the application domain. It can operate both on user input and on external content an agent retrieves during execution, such as web pages or documents.
It is particularly relevant for enterprise applications exposing a language model to external users or untrusted content: a prompt firewall reduces the attack surface without requiring changes to the underlying model, which makes it a practical solution even when using third-party models with no direct control. Several providers now offer prompt firewalls as an independent service, deployable in front of any model or API.
The term spread starting in 2023, when the growth of AI agents connected to external tools and data made clear the need for a dedicated, reusable protection layer, distinct from both the model and the application using it.
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