What This Stack Does
LLM applications fail in ways that traditional monitoring cannot detect. A model can return 200 OK while hallucinating, producing toxic content, or ignoring instructions entirely. This stack assembles four complementary tools that together provide complete visibility from the infrastructure layer to output quality. Langfuse traces every LLM call with full context and evaluates output quality systematically. Helicone logs requests with cost analytics and latency breakdowns. Portkey routes requests across providers with caching and failover. Sentry catches the application-level errors that surround your LLM calls.
The Bottom Line
The layered approach matters because no single tool covers the full observability spectrum. Portkey operates at the gateway level, preventing outages through automatic failover and reducing costs through request caching. Langfuse operates at the application level, tracing multi-step agent workflows and scoring output quality. Helicone provides the analytics layer showing cost trends, latency distributions, and usage patterns across models. Sentry catches the exceptions and performance issues in your non-LLM code that affect the overall user experience. Together they form a comprehensive monitoring stack that costs nothing to start with free tiers across all four tools.