Updated March 10, 2026
Agenta is an open-source platform for prompt engineering, evaluation, and experimentation. It provides a prompt playground, version control for prompts, A/B testing, and evaluation pipelines. Teams can iterate on prompts collaboratively, track experiments, and deploy optimized prompts to production.
Helicone is an open-source LLM observability and proxy platform. By adding a single line of code, developers get request logging, cost tracking, caching, rate limiting, and analytics for their LLM applications. Helicone supports all major LLM providers and offers both proxy and async logging modes. Popular with startups for its generous free tier and simple integration.
What each tool does well, and the limitations to keep in mind.
Pros
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Respan lets you trace LLM and agent calls across any model or framework, A/B test prompts on production traffic, and route requests across 500+ models through one gateway.