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Your AI feature is live. Which tool tells you how it fails?
Each page puts three.dev next to one tool you may be weighing, or reviews the best alternatives to it. It says where the other tool is the better choice, lists its prices on the day we checked, and links to the sources.
three.dev vs another tool
three.dev vs Braintrust
three.dev vs Braintrust (2026): which one fits your AI feature?
Braintrust is built around datasets, scorers, and CI, with failure discovery you turn on per project. three.dev scores live traffic and names the failure modes with no setup. Here is where each one fits.
three.dev vs Langfuse
three.dev vs Langfuse (2026): which one fits your AI feature?
Langfuse gives you open-source tracing and evals that you set up and run. three.dev names your failure modes from live traffic with nothing to configure. Here is where each one fits.
three.dev vs LangSmith
three.dev vs LangSmith (2026): which one fits your AI feature?
LangSmith runs the whole agent lifecycle, and its Engine finds failures on paid plans. three.dev finds them without moving your stack onto a platform. Here is where each one fits.
Alternatives to a tool you use
Langfuse alternatives
6 best Langfuse alternatives in 2026
The best Langfuse alternatives in 2026: three.dev, LangSmith, Braintrust, Raindrop, Arize Phoenix, and Opik. What each is best for, what it costs, which are open source, and which find production failures for you.
LangSmith alternatives
6 best LangSmith alternatives in 2026
The best LangSmith alternatives in 2026: three.dev, Langfuse, Braintrust, Raindrop, Arize Phoenix, and Opik. Which drop per-seat pricing, which you can self-host, what each costs, and which find production failures for you.
Braintrust alternatives
6 best Braintrust alternatives in 2026
The best Braintrust alternatives in 2026: three.dev, Langfuse, LangSmith, Raindrop, Arize Phoenix, and Opik. Which cost less than $249 a month, which are open source, and which find production failures for you.
See how your AI feature fails.
Point the AI SDK you already use at one base URL, and get your failure modes named and ranked by severity.