What Helicone and Langfuse are built for
Both are LLM engineering platforms centered on observability: request logging, hierarchical traces, prompt management, and evaluation. Langfuse is open-source and self-hostable with a generous free tier; Helicone focuses on proxy-based logging and analytics. Both compute a "cost" figure by multiplying your logged token counts against a pricing table built into the product.
The gap: an internal pricing table is not a live feed
Because that cost dashboard runs on a pricing table baked into the product, a rate change at OpenAI or Anthropic only reaches your numbers after the vendor ships it and the observability tool updates its table — typically after you have already been billed at the new rate. Neither tool is designed to catch a change before it hits an invoice.
What VendorSpies does instead
VendorSpies is not an observability platform — it never logs a prompt, a trace, or a request. It watches the public rate cards of 30+ AI vendors directly and sends a free alert the moment one changes, independent of what your application has actually called.
Most teams run one of these plus VendorSpies
If Helicone or Langfuse is already wired into your app for tracing and evaluation, that is a different job worth keeping. Add VendorSpies alongside it as the early-warning layer for the vendor side of the equation — no instrumentation or code changes required.