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Evaluate, experiment, and optimize AI products in real time with open-source LLM tracing.

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Tracked since2026
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The Bottom Line

Entry price

Free plan available, paid tiers above

Biggest pro

Open-source and self-hostable, offering flexibility and no vendor lock-in.

Biggest con

Advanced features like dedicated support and custom data limits are only available in higher-tier paid plans.

TL;DR - Phoenix

  • Open-source LLM tracing and evaluation platform.
  • Provides real-time visibility, debugging, and optimization for AI products.
  • Features interactive prompt playgrounds, evaluation libraries, and dataset visualization.
Pricing: Free plan available
Best for: Growing teams

What is Phoenix?

Editorial review
Phoenix is an open-source platform designed for evaluating, experimenting with, and optimizing AI products, specifically Large Language Models (LLMs). It provides comprehensive LLM observability by allowing users to trace, visualize, and debug LLM applications in real-time. Built on OpenTelemetry, Phoenix offers seamless data collection, transparency, and avoids vendor lock-in. The tool is ideal for AI engineers, developers, and data scientists working with LLMs who need to understand model behavior, identify failures, and improve performance. It helps in debugging complex LLM decision-making, flagging poor responses, and troubleshooting issues related to retrieval and tool execution. Phoenix aims to integrate observability directly into the development process, encouraging continuous improvement of LLM applications before and after deployment. Key functionalities include interactive prompt playgrounds for iteration, streamlined evaluation libraries with pre-built templates and human feedback integration, and dataset clustering/visualization to uncover performance issues using embeddings. Its open-source nature and self-hostable option provide flexibility and control for small teams to large enterprises.

Available on: Web

Pros & Cons

Pros

  • Open-source and self-hostable, offering flexibility and no vendor lock-in.
  • Provides deep observability into LLM behavior and decision-making.
  • Facilitates rapid experimentation and iteration with interactive playgrounds.
  • Supports both automated and human feedback for comprehensive evaluations.
  • Strong community support and integrations with popular LLM frameworks.

Cons

  • Advanced features like dedicated support and custom data limits are only available in higher-tier paid plans.
  • The free SaaS tier has limited trace spans and ingestion volume.
  • Requires some technical expertise for self-hosting and full utilization.

Preview

Key Features

OpenTelemetry (OTEL) for seamless setup and data collectionApplication tracing for total visibility into LLM app dataInteractive prompt playground for prompt and model iterationStreamlined evaluation and annotation library with pre-built templatesDataset clustering and visualization using embeddingsSelf-hostable with no feature gates or restrictionsIntegration with various LLM tools and frameworksOnline and offline evaluations, including LLM as judge and code evals

Pricing Plans

Pricing checked Jul 12, 2026

Phoenix Small teams and smaller data

Free & open source

  • Trace spans user managed
  • Ingestion volume user managed
  • Projects user managed
  • Retention user managed
  • Support add-on dedicated support

AX Free

Free

  • 25k trace spans per month
  • 1 GB ingestion volume per month
  • 7 days retention
  • Alyx (Arize agent)
  • Online evals
  • Product observability (monitors & custom metrics)
  • Community support

AX Pro

$50 / month

  • 50k trace spans per month
  • 10 GB ingestion volume per month
  • 15 days retention
  • Everything in AX Free
  • Higher rate limits
  • Longer retention
  • Email support

AX Enterprise

Custom

  • Custom trace spans
  • Custom ingestion volume
  • Custom projects
  • Configurable retention
  • Everything in AX Pro
  • Dedicated support
  • Uptime SLA
  • Custom data limits

Is Phoenix worth the price?

85/100

Phoenix offers a very generous free tier with its open-source solution and a substantial free tier for AX, making it highly accessible.

The AX Pro tier at $50/month provides good value for growing teams needing more capacity. This pricing structure is best for individual developers and small to medium-sized teams focused on AI product evaluation and optimization.

Hidden Costs & Gotchas

Overage fees for exceeding trace spans/ingestion

Add-ons for dedicated support

Self-hosting is an add-on

Enterprise features are custom priced

How Phoenix Compares to Competitors

Compared to similar LLM observability platforms like LangChain Hub (which has a free tier but scales quickly), Phoenix's AX Pro at $50/month offers a competitive amount of trace spans and ingestion volume. While some platforms might offer more features in their free tiers, Phoenix's open-source option provides unparalleled flexibility and cost control for those willing to self-manage.

How Phoenix's pricing compares

At $50/mo, Phoenix is mid-range of its 3 direct competitors ($19 to $100/mo across the set).

Entry paid plan, monthly. Pricing checked Jul 12, 2026.

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Phoenix FAQ

How does Phoenix help in optimizing AI products?

Phoenix optimizes AI products by providing comprehensive LLM observability, allowing users to trace, visualize, and debug LLM applications in real-time. It facilitates rapid experimentation with interactive prompt playgrounds and streamlines evaluation through libraries and human feedback integration.

Which teams benefit most from using Phoenix?

Phoenix is ideal for AI engineers, developers, and data scientists working with LLMs. These teams can use it to understand model behavior, identify failures, debug complex decision-making, and improve the performance of their LLM applications.

How does Phoenix compare to LangSmith?

Phoenix, like LangSmith, offers tools for observing and debugging LLM applications. However, Phoenix distinguishes itself by being open-source and self-hostable, which provides flexibility and helps avoid vendor lock-in.

What kind of limitations should users be aware of with Phoenix?

Users should note that advanced features, such as dedicated support and custom data limits, are reserved for higher-tier paid plans. The free SaaS tier also has limitations on trace spans and ingestion volume, and self-hosting requires some technical expertise.

How is Phoenix priced?

Phoenix is available on a free tier, which offers basic usage. For users requiring more extensive usage and additional features, paid plans are available.

Can Phoenix integrate with existing LLM development workflows?

Yes, Phoenix is built on OpenTelemetry, which allows for seamless data collection and transparency. It also boasts strong community support and integrations with popular LLM frameworks, making it adaptable to various development processes.

How does Phoenix assist in debugging LLM applications?

Phoenix assists in debugging by allowing users to trace and visualize LLM applications in real-time. It helps in identifying and troubleshooting issues related to retrieval and tool execution, flagging poor responses, and understanding complex LLM decision-making.

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