LLM applications are everywhere now, and they’re fundamentally different from traditional software. They’re non-deterministic. They hallucinate. They can fail in ways that are hard to predict or reproduce (and sometimes hilarious). If you’re building LLM-powered products, you need visibility into what’s actually happening when your application runs.
That’s what LLM observability tools are for. These platforms help you trace requests, evaluate outputs, monitor performance, and debug issues before they impact users. In this guide, you’ll learn how to approach your choice of LLM observability platform, and we’ll compare the top tools available in 2025, including open-source options like Opik and commercial platforms like Datadog and LangSmith.
What Is LLM Observability?
LLM observability is the practice of monitoring, tracing, and analyzing every aspect of your LLM application, from the prompts you send to the responses your model generates. The core components include:
- LLM tracing – tracking the lifecycle of user interactions from initial input to final response, including intermediate operations and API calls
- LLM evaluation – measuring output quality through automated metrics like relevance, accuracy, and coherence, plus human feedback
- LLM monitoring in production – tracking latency, throughput, resource utilization, and error rates to ensure system health and keep costs under control
Why LLM Observability Matters
You already know LLMs can fail silently and burn through your budget. Without observability, you’re debugging in the dark. With it, you can trace failures to root causes, detect quality drift, optimize prompts based on real performance, and maintain the audit trails required for compliance. The right observability solution will help you catch issues before users do, understand what’s driving costs, and iterate quickly based on production data.
Key Considerations for Choosing an LLM Observability Platform
When evaluating observability tools, ask yourself these questions to find the right fit for your needs.
What Type of LLM Application Are You Building?
Your use case shapes which features matter most. If you’re primarily monitoring production systems, prioritize real-time alerting and anomaly detection. If you’re iterating during development, look for strong evaluation and experimentation features. Some platforms serve both stages well, while others specialize in one.
It’s also worth understanding whether you need an evaluation-centric or observability-centric platform. Evaluation-centric tools (like Confident AI, Braintrust, and Galileo) excel at measuring output quality, running comprehensive test suites, and comparing prompt variations. Observability-centric tools (like Helicone, or Phoenix) prioritize operational metrics, tracing, and real-time monitoring. Some platforms like Opik, Langfuse, and LangSmith offer strong capabilities in both areas.
Building agentic systems with complex multi-step workflows? You need platforms with detailed tracing visualization and agent-specific features. Working on RAG applications? Prioritize tools that track retrieval quality, context usage, and can measure metrics like context precision and relevance.
Can You Trace and Replay Complex Workflows?
Look at how the platform handles prompt tracing. Does it capture the complete prompt, including system messages, user input, retrieval context, and metadata like token counts and cost? Can you replay interactions to reproduce issues?
For agentic systems, check whether you can visualize the entire sequence of tool calls and decision points. The best platforms show these workflows as graphs or timelines, making multi-step interactions easy to understand.
How Will You Evaluate Output Quality?
Since LLM responses are subjective and contextual, you need multiple evaluation approaches. Does the platform offer:
- Pre-built LLM evaluation metrics for hallucination detection, factual accuracy, relevance, and toxicity that run automatically on production traffic?
- LLM-as-a-judge capabilities for subjective qualities like helpfulness or tone?
- Ways to collect and incorporate human-in-the-loop feedback from domain experts or end users?
Consider the tradeoffs: automated metrics scale easily but may miss nuance, while human evaluation catches edge cases but doesn’t scale. Some platforms offer cost-effective evaluation using smaller models instead of expensive GPT-4 calls, which matters if you’re scoring high volumes of production traffic.
What Metrics Matter for Your Use Case?
Beyond individual responses, you need aggregate visibility. Can you track latency distributions, error rates, token usage trends, and cost breakdowns by model or feature? Can you slice these metrics by user segments, prompt versions, or A/B test variants?
Think about which metrics actually impact your business, whether that’s cost per conversation, evaluation scores by customer tier, or latency at different traffic levels.
Does it Integrate with Your Existing Stack?
Check compatibility with your LLM providers (OpenAI, Anthropic, Vertex AI), frameworks (LangChain, LlamaIndex, Haystack), vector databases (Pinecone, Weaviate, Qdrant), and MLOps tools.
Consider the integration approach too. Proxy-based tools like Helicone offer the fastest setup with minimal code changes (often just changing your API base URL), while SDK-based platforms give you more control and flexibility but require more integration work. If you’re already using a specific framework like LangChain, native integrations will save significant development time.
Will You Know When Things Go Wrong?
Look for real-time alerting on spikes in errors, latency thresholds, or evaluation scores dropping below acceptable levels. Can you set up alerts for the specific failure modes that matter to your application?
Check whether dashboards surface key metrics at a glance and let you drill down into individual traces when debugging.
Do You Want to Self-Host or Use a Managed Service?
Open-source tools give you transparency, flexibility, and control. You can self-host, customize the code, and avoid vendor lock-in or usage-based pricing that scales with your success. The tradeoff is that you’re responsible for operating the infrastructure, scaling it, and implementing features you need that aren’t in the core product.
Managed platforms handle the operational burden, provide enterprise support, and often include advanced features like real-time guardrails or automated optimization at scale. They make sense when you want to focus engineering resources on your core product rather than observability infrastructure.
Does it Meet Your Security Requirements?
For enterprise deployments, verify SOC 2 compliance, data encryption, role-based access controls, and self-hosting options. Consider where your data will be stored and whether the platform meets regulatory requirements for your industry.
How Will Costs Scale with Your Usage?
Look beyond the base price to understand how costs grow as your application scales. Some platforms charge based on trace volume or data ingested, which can get expensive at high volumes. Others offer flat-rate pricing or generous free tiers.
Consider the total cost equation. Platforms offering cost-effective evaluation or optimization features may offset their own pricing and save you more than they cost.
Top LLM Observability Tools of 2025
The LLM observability options have expanded rapidly, with tools ranging from lightweight open-source libraries to enterprise-grade platforms. Here’s an honest look at the leading options and what makes each one stand out.
At-a-Glance Comparison
| Tool | Best For | Integration | Pricing Model | Key Differentiator |
|---|---|---|---|---|
| Opik | Full lifecycle observability + automated optimization | SDK-based + Native integrations for all major model providers & agent frameworks | Open source, free tier (25k spans/month, unlimited users), Pro $39/month, custom Enterprise | Automated prompt optimization, 7-14x faster performance than other open source tools |
| Langfuse | Self-hosting with comprehensive tracing | SDK-based | Open source, free tier (50k events/month, 2 users), Core $29/month, Pro $199/month, Enterprise $2499/month | Engineering and production-focused, extensive analytics set |
| Arize Phoenix | OpenTelemetry compatibility, no vendor lock-in | OTEL-based | Open source | Built on OpenTelemetry, embedding-based analysis |
| LangSmith | LangChain/LangGraph applications | Native LangChain | Free tier (5k traces/month, 1 user), Plus $39/month, custom Enterprise | Deepest LangChain integration |
| W&B Weave | Teams already using Weights & Biases | SDK-based | Free tier, Pro tier starts at $60/month, custom Enterprise | Multimodal tracking, powerful visualizations |
| Galileo | Enterprise evaluation with real-time guardrails | SDK-based | Free tier (5k traces/month), Pro $100/month, custom Enterprise | Runtime intervention, cost-effective Luna-2 evals |
| Langwatch | OpenTelemetry-native with extensive cost tracking | OTEL-based | Free tier (1k traces), Launch €59/month, Accelerate €199/month, custom Enterprise | Token tracking across 800+ models |
| Braintrust | Non-technical team collaboration | SDK-based | Free tier (1 GB processed data), Pro $249/month, custom Enterprise | UI-driven playground for non-coders |
| DeepEval by Confident AI | Evaluation-first with multi-turn support | API-based | Starter $20/month (20k traces, 1 user), Premium $80/month, custom Enterprise | 5M+ evaluations run, proven metrics |
| MLFlow | ML teams already using MLFlow | Proxy-based | Open source | Same instrumentation for dev and prod |
| Helicone | Fast setup with cost optimization | SDK-based | Free tier (10k requests/month), Pro $20/seat, Team $200/month, custom Enterprise | One-line integration, cost reduction via caching |
| Deepchecks | Systematic testing and validation | SDK-based | Open source, pricing for cloud-hosted options available upon request | Testing-focused evaluation framework |
| Ragas | RAG-specific evaluation | Python library | Open source | Research-backed RAG metrics |
Opik by Comet
What it is: Open-source LLM evaluation and observability platform designed for the complete development lifecycle, from experimentation to production monitoring.
Core strengths:
- Automated prompt optimization with six powerful algorithms and counting (Few-shot Bayesian, evolutionary, LLM-powered MetaPrompt, GEPA, hierarchical reflective, and tool signature optimization) that improve prompts based on your evaluation metrics, saving significant engineering time over manual iteration
- Built-in guardrails that screen user inputs and LLM outputs to block unwanted content before it reaches users (PII, competitor mentions, off-topic discussions), using Opik’s models or third-party libraries
- Comprehensive tracing and evaluation with pre-configured metrics for hallucination detection, factuality, and moderation, plus custom metrics you define
- LLM unit tests built on PyTest that integrate into CI/CD pipelines, letting you establish baselines and catch regressions before deployment
- Exceptional performance: LLM evaluation framework benchmarks show Opik completes trace logging and evaluation in ~23 seconds, compared to Phoenix’s ~170 seconds and Langfuse’s ~327 seconds, which makes it 7-14x faster for rapid iteration
Integration: Works with any LLM provider out of the box, plus native integrations for LangChain, LlamaIndex, OpenAI, Anthropic, Vertex AI, and more.
Pricing: Truly open-source with full features available in the codebase. Free hosted plan includes 25k spans per month with unlimited team members and 60-day data retention. Pro plan is $39/month for 100k spans, with additional capacity at $5 per 100k spans.
Best for: Teams that want comprehensive observability with automated optimization, those working on both model development and application deployment, and organizations that need flexible deployment options (cloud or self-hosted).
Langfuse
What it is: Open-source LLM engineering platform focused on comprehensive tracing, prompt management, and analytics.
Core strengths:
- Deep, asynchronous tracing with detailed visibility into complex workflows
- Robust prompt management with versioning, programmatic deployment, and experimentation capabilities
- Extensive analytics with dozens of features including session tracking, batch exports, and SOC2 compliance
- Centralized PostgreSQL database architecture makes self-hosting straightforward (though may have scaling implications for very high-volume deployments compared to distributed approaches)
Integration: SDK-based integration with Python and TypeScript. Works with all major LLM providers and frameworks.
Pricing: Free self-hosting. Cloud version is free up to 50k events per month (2 users, 30-day data retention), then $29/month for 100k events with additional 100k events at $8/month plus 90-day retention.
Best for: Teams prioritizing self-hosting, those who need detailed tracing and granular control for complex multi-step workflows, and production-focused organizations.
Arize Phoenix
What it is: Open-source observability solution built on OpenTelemetry for framework-agnostic tracing and evaluation.
Core strengths:
- Built on OpenTelemetry and provides no vendor lock-in, so you can export traces to any OTEL-compatible tool
- Automatic instrumentation and evaluation library with pre-built templates for easy setup, with manual control and customization available when needed
- Fast, flexible sandbox for prompt and model iteration so you can compare prompts, visualize outputs, and debug failures without leaving your workflow
- Uses embeddings to uncover semantically similar questions, document chunks, and responses, helping isolate poor performance patterns
Integration: Framework and language agnostic through OpenTelemetry. Integrates with LangChain, LlamaIndex, and other major frameworks.
Pricing: Fully open-source and self-hostable with no feature gates or restrictions.
Best for: Teams that want OpenTelemetry compatibility, those concerned about vendor lock-in, and organizations that need flexibility to integrate with existing observability stacks.
LangSmith by LangChain
What it is: End-to-end observability and evaluation platform with deep integration into the LangChain ecosystem.
Core strengths:
- Tightest integration and lowest friction observability if you’re building with LangChain or LangGraph
- Automatically tracks inputs, outputs, intermediate steps, tool usage, and memory chains in LangChain applications
- Native support for LangGraph with integrated evaluations, prompt version control, and conversational feedback overlays
- Less useful if you’re not using LangChain, so teams with custom implementations or other frameworks may find integration more cumbersome
Integration: Deep LangChain/LangGraph integration with automatic tracing. Supports Python and JavaScript SDKs.
Pricing: Free tier available for one person and 5k traces/month. Paid plans required for production start at $39 per user per month for 10k traces, then pay-as-you-go based on trace volume.
Best for: Teams heavily invested in the LangChain ecosystem, those building agentic workflows with LangGraph, and organizations wanting the simplest path to observability for LangChain apps.
W&B Weave
What it is: Weights & Biases’ framework for LLM experimentation, tracing, and evaluation, extending their mature ML platform to support LLMs.
Core strengths:
- Powerful visualizations for objective comparisons with automatic versioning of datasets, code, and scorers
- Interactive playground for prompt iteration with support for any LLM
- Multimodal tracking, including text, code, documents, images, and audio
- Online evaluations score live production traces without impacting performance for real-time monitoring
- Purpose-built features for agentic systems, integrating with OpenAI Agents SDK and protocols like MCP
- Extends existing Weights & Biases workspace to LLMs, eliminating need for separate tools if you already use W&B
- Can become expensive at scale, especially for high-volume applications
Integration: Works with any LLM and framework. Out-of-the-box integrations for OpenAI, Anthropic, and major agent frameworks.
Pricing: Free developer tier and Pro plan available for $60/month, both with limits on storage and data ingestion. Enterprise pricing based on usage and scale.
Best for: Teams already using Weights & Biases for ML experiments, those building state-of-the-art agents, and organizations that prioritize visualization and iteration speed.
Galileo
What it is: Enterprise AI reliability platform focused on evaluation intelligence, guardrails, and real-time protection.
Core strengths:
- Evaluation-centric Insights Engine automatically surfaces exact failure patterns (tool errors, planning breakdowns, infinite loops) that generic observability tools miss
- Over 20 pre-built evaluators that are tested and accurate, plus auto-generated custom LLM-as-a-judge evaluators created by typing a description
- CLHF (Continuous Learning with Human Feedback) auto-tunes evaluators by adding few-shot examples based on human annotations
- Agent Protect provides runtime intervention, and intercepts problematic outputs before they reach users
- Evaluation using Luna-2 SLMs, which Galileo says is cheaper and faster than GPT alternatives
Integration: SDKs and APIs for Python and TypeScript. Integrates with major LLM providers and frameworks.
Pricing: Free developer tier with 5k traces/month and Pro for $100/month with 50k traces. Enterprise pricing with flexible deployment options.
Best for: Enterprise teams with strict compliance requirements, those needing real-time guardrails and intervention, and organizations prioritizing safety and evaluation at scale.
Langwatch
What it is: Framework-agnostic LLM observability platform built with OpenTelemetry compatibility.
Core strengths:
- Extensive metrics for AI engineers and product teams, including prompt/output tracing, metadata-rich logs, latency and error monitoring with real-time alerting
- Token cost tracking across 800+ models and providers
- Automatically threads multi-turn agent conversations for complete traceability
- Attach custom metadata (user IDs, session context, features used) for deeper filtering and analysis
- All analytics and logs exportable via API or webhook for downstream analysis
- Automatic prompt tuning based on evaluation feedback
Integration: OpenTelemetry native with no lock-in. Integrates with all major frameworks and providers.
Pricing: Free tier (1k traces/month), Launch €59/month (20k traces), Accelerate €199/month, Enterprise custom pricing.
Best for: Teams that prioritize OpenTelemetry compatibility, those needing extensive cost tracking across many models, and product teams that want user journey analytics.
Braintrust
What it is: End-to-end platform for building AI apps with emphasis on evaluation and testing.
Core strengths:
- Iterative LLM workflows with detailed evaluation capabilities
- Eval system built around three components: prompts (tweak from any AI provider), scorers (industry-standard autoevals or custom), and datasets (versioned, integrated, secure)
- Designed for both technical and non-technical team members with features bidirectionally synced between code and UI, making it very accessible for product managers and domain experts
- Online evaluations continuously score production logs asynchronously for real-world monitoring
- Functions let you define custom scorers or callable tools in TypeScript and Python
- Self-hosting support for teams needing full control over data and compliance
Integration: SDK integration for TypeScript and Python. Works with major LLM providers.
Pricing: Free tier (1M trace spans, 10k scores, 14-day retention), Pro $249/month (unlimited spans, 5GB data), Enterprise custom pricing.
Best for: Teams that prioritize evaluation over observability, and those wanting intuitive tools for non-technical stakeholders.
DeepEval by Confident AI
What it is: LLM observability and evaluation powered by the open-source DeepEval framework.
Core strengths:
- Advanced logging lets you recreate scenarios where monitored responses were generated
- Easy A/B testing of different hyperparameters in production (prompt templates, models, etc.)
- Setup takes less than 10 minutes via API calls through DeepEval
- Real-time evaluations automatically grade incoming responses across any use case or LLM system (RAG, chatbots, agents)
- Supports both single-turn and multi-turn conversational evaluation for chatbots and agentic systems
- Detailed tracing from retrieval data to API calls helps pinpoint where things went wrong
- Collect feedback from human annotators on the platform or directly from end users via API
Integration: One-line integrations for LangChain, LlamaIndex, and 5+ frameworks. Custom tracing for applications not built with frameworks.
Pricing: Free tier available, but less robust than what other tools on this list offer. Starter tier from $20/user/month (20k traces), Premium from $80/user/month (75k traces), custom Enterprise pricing available.
Best for: Teams that want proven evaluation metrics, those needing quick setup, and organizations prioritizing A/B testing in production.
MLFlow
What it is: Open-source platform for the ML lifecycle that has expanded to support gen AI observability and evaluation.
Core strengths:
- Tracing captures inputs, outputs, and step-by-step execution including prompts, retrievals, and tool calls
- Tracks cost and latency for each step of your application
- Same trace instrumentation works for both development and production so you get consistent insights across environments
- 1-line-of-code integrations for over 20 popular LLM SDKs and frameworks with intuitive APIs for customization
- Established platform with full OpenTelemetry compatibility, giving you total ownership and portability of your data
- Visualization UI helps understand execution flow and review many traces at once
Integration: Automatic instrumentation for 20+ frameworks. Fully OpenTelemetry compatible.
Pricing: Free and open-source. Self-hosted or managed cloud options available.
Best for: Teams already using MLFlow for ML workflows, those wanting a mature open-source option, and organizations needing OpenTelemetry compatibility.
Datadog LLM Observability
What it is: Enterprise observability platform that has extended its monitoring capabilities to LLMs.
Core strengths:
- Extends existing Datadog setup if you’re already using it for infrastructure and application monitoring to provide unified visibility across your entire stack
- Enterprise-grade features including compliance, security, advanced alerting, and integration with broader observability platform
- Built for scale and reliability with SLAs and support for high-volume production deployments
- Enterprise-focused and can be expensive, especially for smaller teams or those just getting started with LLM observability
Integration: Integrates with major LLM providers and frameworks through their monitoring SDKs.
Pricing: $8/month per 10k monitored LLM requests when billed annually. However there is a minimum commitment of 100k LLM requests per month, which means the true price starts at $80/month and increases with usage.
Best for: Large enterprises already using Datadog, teams needing unified observability across infrastructure and LLMs, and organizations with complex compliance requirements.
Helicone
What it is: Open-source LLM observability platform with proxy-based integration and AI gateway capabilities.
Core strengths:
- Observability-centric with strong operational focus, proxy-based approach means minimal code changes and automatic logging
- Built-in caching can reduce API costs by serving cached responses without invoking the LLM
- Runs on Cloudflare Workers, providing low latency and efficient global routing
- Prompt management with versioning and experimentation
- Session tracking to follow multi-step interactions
- Integration with evaluation platforms like LastMile and Ragas
- Self-hosting support for teams needing full control
- SOC 2, GDPR, and HIPAA compliant, so suitable for healthcare and other regulated industries
Integration: Proxy-based integration by changing your API base URL. Works with OpenAI, Anthropic, Azure, and 20+ other providers.
Pricing: Free tier (10k logs/month, 1-month data retention), Pro starts at $20/seat/month and 10k logs, Team is $200/month (10k logs with unlimited seats), custom Enterprise.
Best for: Teams that want minimal setup effort and quick implementation, and organizations prioritizing cost optimization through caching.
Deepchecks
What it is: LLM evaluation and validation platform focused on testing and quality assurance.
Core strengths:
- Specializes in systematic evaluation of LLM applications with comprehensive testing frameworks
- Validates model outputs, detects data issues, and ensures consistent quality across deployments
- More evaluation-focused than observability-focused, providing testing infrastructure for reliability as you iterate
Integration: Python SDK with support for major frameworks and model providers.
Pricing: Open-source with cloud-hosted tier options including Basic, Scale, and Enterprise. Pricing available upon request.
Best for: Teams prioritizing testing and validation, QA-focused organizations, and those needing systematic evaluation frameworks.
Ragas
What it is: Open-source framework for RAG (Retrieval-Augmented Generation) evaluation with observability integrations.
Core strengths:
- Focuses specifically on evaluating RAG systems with metrics for context precision, context recall, faithfulness, and answer relevance
- Provides research-backed evaluation approaches tailored to retrieval-based applications
- Integrates with observability platforms to provide evaluation metrics alongside your traces
Integration: Python library that integrates with observability platforms. Works with popular RAG frameworks.
Pricing: Open-source and free to use.
Best for: Teams building RAG applications, those needing specialized retrieval evaluation, and organizations wanting research-backed metrics.
Building Reliable LLM Systems Through Observability
Using an observability solution means you can ship your LLM application confidently. The right observability platform will provide:
- Transparency into what your LLM is actually doing
- Reliability through early detection of issues and systematic evaluation
- Performance insights from detailed tracing and cost tracking
- The ability to iterate quickly based on real production data
Whether you choose an open-source tool like Opik for its automated optimization capabilities, a specialized platform like Galileo for its guardrails and enterprise features, or a framework-specific option like LangSmith for deep LangChain integration, the important thing is to implement observability before you hit production.
Get started today with Opik, no credit card needed. It’s truly open-source, free to try, and built for the complete LLM development lifecycle from experimentation to production monitoring.
