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LangWatch

Free

An Open Source tool for observing, evaluating and optimising your llm apps and prompts, which supports LangChain out of the box! ![GitHub Repo stars](https://img.shields.io/github/stars/langwatch/langwatch?style=social)

FreeFree tier
Type
Open Source
Visit Website GitHub (40 stars)

About LangWatch

LangWatch is an open-source platform for LLM evaluations and AI agent testing. It enables teams to test, simulate, evaluate, and monitor LLM-powered agents end-to-end—before release and in production. It offers end-to-end agent simulations with realistic scenarios, a unified loop for tracing, dataset creation, evaluation, and prompt optimization, and is built on open standards like OpenTelemetry (OTLP) for framework and provider agnosticism. It includes an AI Gateway with a proxy for governance, cost control, and fallback across providers. Collaboration features include run reviews, annotation queues, and GitHub integration for versioning prompts. LangWatch supports cloud and self-hosted deployments.

Key Features

End-to-end agent simulations with realistic scenarios and user simulators
Eval + observability + prompts in one loop: trace → dataset → evaluate → optimize → re-test
OpenTelemetry/OTLP-native, framework and LLM-provider agnostic
AI Gateway with virtual keys, hierarchical budgets, guardrails, and automatic fallback across providers
Collaboration via annotation queues, GitHub integration for prompt versioning, and run review
Supports cloud (free tier) and self-hosted local setup

Pros & Cons

Pros
  • Open-source and self-hostable, giving full data control
  • No vendor lock-in due to open standards (OTLP)
  • Provides end-to-end visibility from simulation to production
  • Integrated AI gateway for cost management and fallback
  • Designed for team collaboration with annotation and Git integration

Best For

Regression testing of LLM agents before releaseProduction monitoring of LLM-powered applicationsSimulating user interactions to identify agent failuresEvaluating and optimizing prompts and models in a unified workflowControlling costs and governance with an AI gateway