Free and open first
Best AI LLM Observability Tools in 2026
For software built around large language models, observability tools can help you inspect requests, failures, outputs, performance, and token costs. Compare LLM trace capture and failure tracking with latency metrics, output evaluations, and token cost tracking. Free-plan availability, retention, and paid starting prices add practical dimensions to the comparison. OpenLIT, W&B Weave, and Opik are among the named tools. Consider which signals you need to follow and whether your focus is diagnosing issues, reviewing outputs, or understanding latency and token costs.
- 23 apps
- Research read 23 Sept 2026
- How the order is worked out
- 1
Agenta
Free plan Open source APISelf-hostedWebAgenta combines agent-building, automation, and run observability, with both cloud and self-hosted options.
- 2
Langfuse
Free plan Open source APILinuxSelf-hosted+1Langfuse brings tracing, prompt workflows, and evaluation features into one AI engineering platform, with both hosted and self-hosted options.
- 3
LangWatch
Free plan Open source APILinuxMac+2LangWatch brings agent simulation, evaluation, tracing, and deployment options together for teams working toward production.
- 4
MLflow Tracing
Free plan Open source APILinuxSelf-hosted+1Choose MLflow Tracing if you need free, open-source tracing with detailed spans and broad LLM framework integrations, while keeping trace data on your infrastructure.
- 5
OpenLIT
Free plan Open source APILinuxMac+3Choose OpenLIT if you want LLM tracing, evaluations, prompt tools, and cost tracking, with the option to self-host under an Apache 2.0 license.
- 6
Lunary
Free plan Open source APISelf-hostedWebLunary combines LLM observability with analytics, prompt management, and response evaluation.
- 7
Opik
Free plan Open source APILinuxMac+3Opik brings tracing, evaluation, testing, and production monitoring into one platform, with both cloud and self-hosted options.
- 8
W&B Weave
Free plan Open source APIiPhoneLinux+4W&B Weave brings tracing, evaluation, monitoring, and safety scoring together for production AI agents.
- 9
TruLens
Free plan Open source APISelf-hostedTruLens offers tracing, evaluation, and version comparison for AI applications, with customizable metrics and self-hosted storage options.
- 10
Arize AX
Free plan APISelf-hostedWebArize AX combines tracing, evaluations and experiments with tools for investigating agent failures.
- 11
Arize Phoenix
Free plan APISelf-hostedWebPhoenix brings tracing, evaluation, prompt inspection, and dataset experiments to AI application teams. It is free and open source, with deployment choices and usage management left to users.
- 12
Braintrust
Free plan APISelf-hostedWebBraintrust combines production trace inspection with dataset evaluations and prompt iteration.
- 13
Confident AI
Free plan APISelf-hostedWebConfident AI brings development evaluations, production tracing, alerting, and safety testing into one platform. The free plan has defined usage limits, while paid plans start at $200 per month.
- 14
Fiddler AI
Free plan APISelf-hostedWeb - 15
Galileo
Free plan APISelf-hostedWebGalileo combines evaluation, observability, and guardrails with several deployment options and developer interfaces. Check the trace allowance and SSO availability against your deployment needs.
- 16
Helicone
Free plan APISelf-hostedWebHelicone brings routing and observability tools together, with a free tier and self-hosting options. Its maintenance-mode status is worth weighing when considering it for a new deployment.
- 17
HoneyHive
Free plan APISelf-hostedWebHoneyHive covers trace inspection, evaluations, live monitoring, and version experiments for AI agents. Teams should compare the free plan’s limits with their event volume and retention needs.
- 18
LangSmith
Free plan APILinuxMac+3LangSmith combines agent evaluation with prompt tools and observability, including cost and trajectory tracking.
- 19
Maxim AI
Free plan APISelf-hostedWebMaxim AI brings prompt work, agent evaluation, and production observability into one platform.
- 20
OpenLLMetry
Free plan APISelf-hostedWebOpenLLMetry combines tracing, token cost tracking, and integrations for LLM applications in a free, Apache-2.0-licensed project.
- 21
Portkey
Free plan APISelf-hostedWebPortkey brings model access, prompt management, and activity monitoring under one platform. Review the plan's log retention, deployment, and support terms against your team's requirements.
- 22
PromptLayer
Free plan APISelf-hostedWebPromptLayer brings prompt editing, evaluation, and operational monitoring into one workflow, with collaboration features for technical and non-technical contributors.
- 23
Respan (formerly Keywords AI)
Free plan APISelf-hostedWebRespan combines model routing with tracing, evaluation, and monitoring in one product. Check the gateway's possible latency and plan terms against your requirements before choosing it.
#1Places #1, #2, #3, #4, #5 on this list can be bought by the makers of the software on it. See the price