Halo

Quick answer

Halo — Effortlessly log and observe every LLM request and response. It's free. Best for debugging unexpected or incorrect LLM outputs during development.

Halo is a free, open-source logging and observability tool designed specifically for developers building LLM-powered applications, enabling them to record, inspect, and analyze every request and response flowing through their AI systems. Built for engineers who need full visibility into how their language model integrations are behaving in real time, Halo fills a critical gap in the LLM development workflow by providing structured logging without requiring expensive third-party SaaS subscriptions. Whether you are debugging unexpected model outputs, auditing prompt performance, or monitoring latency across different API calls, Halo gives you the raw data you need to understand what is happening inside your application. Because it is open-source and self-hosted, teams retain complete control over their observability data, making it an appealing choice for organizations with strict data privacy requirements or those who simply prefer not to send sensitive prompts to external services. Halo is lightweight, developer-friendly, and easy to integrate into existing LLM pipelines, making it a practical starting point for any team that wants better insight into their AI application behavior without added cost or complexity.