Best AI LLM Observability Tools in 2026
Updated
In short: OpenLIT is ranked #1 of 23 as of 4 October 2026, ahead of W&B Weave and Opik. The best-ranked option with a free plan is W&B Weave. The lowest first paid tier on this page is Respan (formerly Keywords AI) at $16.58/mo.
For teams building or running applications with large language models, observability tools offer ways to track failures, inspect traces, assess outputs, and monitor costs. The ranked options are compared on failure tracking, LLM trace capture, latency metrics, output evaluations, and token cost tracking. Free-plan availability and retention, along with paid-from pricing, are also included. Arize AX, Langfuse, and Opik appear among the first entries, followed by W&B Weave and Arize Phoenix. Weigh which signals and evaluation details are relevant to your work, and compare the listed plan terms alongside the capabilities.
23 AI LLM observability tools ranked on what their makers publish — plans and prices, free tiers, platforms and the facts on their own pages.
15 of the 23 here have a free tier you can use, 0 have open-source code on record, and 0 have full bars: free, open, on most of your devices and documented.
| # | App | Signal | Free tier | Open code | Devices | From | Score |
|---|---|---|---|---|---|---|---|
| 1 | OpenLITWeb · Windows · Mac · Linux · Self-hosted · API | Three bars | — | 4 of 6 | Free | 6.6 | |
| 2 | W&B WeaveWeb · Windows · Mac · Linux · Self-hosted · API | Three bars | — | 4 of 6 | $60/mo | 6.6 | |
| 3 | OpikWeb · Linux · Self-hosted · API | Two bars | — | 2 of 6 | $19/mo | 6.5 | |
| 4 | AgentaWeb · Self-hosted · API | Two bars | — | 1 of 6 | $29/mo | 6.4 | |
| 5 | Arize AXWeb · Self-hosted · API | Two bars | — | 1 of 6 | $50/mo | 6.4 | |
| 6 | BraintrustWeb · Self-hosted · API | Two bars | — | 1 of 6 | $249/mo | 6.4 | |
| 7 | Confident AIWeb · Self-hosted · API | Two bars | — | 1 of 6 | $200/mo | 6.4 | |
| 8 | GalileoWeb · Self-hosted · API | Two bars | — | 1 of 6 | $100/mo | 6.4 | |
| 9 | HeliconeWeb · Self-hosted · API | Two bars | — | 1 of 6 | $79/mo | 6.4 | |
| 10 | LangfuseWeb · Self-hosted · API | Two bars | — | 1 of 6 | $29/mo | 6.4 | |
| 11 | Maxim AIWeb · Self-hosted · API | Two bars | — | 1 of 6 | $29/mo | 6.4 | |
| 12 | MLflow TracingWeb · Self-hosted · API | Two bars | — | 1 of 6 | Free | 6.4 | |
| 13 | PortkeyWeb · Self-hosted · API | Two bars | — | 1 of 6 | $49/mo | 6.4 | |
| 14 | PromptLayerWeb · Self-hosted · API | Two bars | — | 1 of 6 | $49/mo | 6.4 | |
| 15 | Respan (formerly Keywords AI)Web · Self-hosted · API | Two bars | — | 1 of 6 | $16.58/mo | 6.4 | |
| 16 | Fiddler AIWeb | No signal | — | — | 1 of 6 | — | 5.2 |
| 17 | LangSmithWeb | No signal | — | — | 1 of 6 | — | 5.2 |
| 18 | LangWatchWeb · Linux | No signal | — | — | 2 of 6 | — | 5.2 |
| 19 | Arize PhoenixWeb | No signal | — | — | 1 of 6 | — | 5.1 |
| 20 | HoneyHiveWeb | No signal | — | — | 1 of 6 | — | 5.1 |
| 21 | OpenLLMetryNo platforms listed | No signal | — | — | 0 of 6 | — | 5.0 |
| 22 | TruLensNo platforms listed | No signal | — | — | 0 of 6 | — | 4.8 |
| 23 | LunaryWeb | No signal | — | — | 1 of 6 | — | 4.7 |
Is your app on this list?
Numbered spots on this list can be sponsored. They are labelled, and the editorial order and scores never change for payment.
Questions about this list
Which AI LLM observability tool is ranked first on Freedom251?
OpenLIT is ranked #1 of 23 with a score of 6.6. W&B Weave is second and Opik third.
How many of these have a free plan?
15 of the 23 on this page publish a free plan on their own pricing pages.
Which is the cheapest paid option?
On this page, Respan (formerly Keywords AI) has the lowest first paid tier we found: $16.58/mo.
How is this list ranked?
Ranked free-and-open first: a usable free tier and open-source code, then the platforms it runs on and its documentation. Paid placements never change a rank.