Pick NeMo Guardrails if
app teams who will write Colang and run rails in their own process.
Read the NeMo Guardrails pageNeMo Guardrails vs Phoenix
Our take
Pick NeMo Guardrails if you're on a app team who will write Colang and run rails in their own process. Pick Phoenix if you're on a agent team who will self-host Phoenix for $0 (uvx arize-phoenix serve) and only open Arize AX when they want a managed cloud. Skip NeMo Guardrails if you're on a team that want a scan CLI without rails (Garak) or a YAML CI eval (Promptfoo).
Best for
NeMo Guardrails Runtime guardrails you start at $0
Phoenix See why an agent failed and prove a fix
Free plan
NeMo Guardrails $0 · apache-2.0. Library + Colang. You pay model inference
Phoenix $0 · local / Docker / Kubernetes. You bring compute. Homepage: uvx arize-phoenix serve
Lowest paid
NeMo Guardrails Not published by the vendor
Phoenix AX Pro $50/mo
Runs where
NeMo Guardrails Hosted
Phoenix Hosted
Watch out
NeMo Guardrails $0 is the library, not the model bill
Phoenix ELv2, not Apache
Last checked
NeMo Guardrails 2026-10-28 · github.com/NVIDIA-NeMo/Guardrails
Phoenix 2026-10-27 · arize.com/pricing
Which one, then?
Pick Phoenix if
agent teams who will self-host Phoenix for $0 (uvx arize-phoenix serve) and only open Arize AX when they want a managed cloud.
Read the Phoenix page