Promptfoo is a tool designed to test the security of LangChain applications by conducting adversarial testing, also known as red teaming. This process involves using adversarial language models to identify potential vulnerabilities in LangChain chains and agents. The guide outlines a systematic approach, starting with setting up the environment and creating a LangChain provider, followed by defining a red teaming configuration through a YAML file. Plugins and strategies are core to the testing process, with plugins targeting specific risks like harmful content and security vulnerabilities, while strategies define how adversarial inputs are delivered to maximize attack success. The red teaming evaluation is executed via command-line instructions, generating a report that highlights vulnerabilities, unexpected agent behaviors, and safety bypasses, along with recommendations for improving security. To address identified issues, common mitigation strategies include input validation, output parsers, and human approval steps, with a re-evaluation advised after implementing fixes.