The 10 Best AI Observability Tools for RAG Pipelines in 2027
By Kory White · Updated Nov 2026 · 6 min read
Direct answer
LangSmith is the best AI observability tool for RAG pipelines: it traces the retrieval step, and its own tutorial defines four RAG evaluators, including groundedness and retrieval relevance. Comet Opik is #2 with retrieval tracing, a ContextPrecision metric and a $19 a month cloud plan. TruLens is #3, free under the MIT license, with RAG triad scoring.
OpenLLMetry is free under the Apache-2.0 license; the Traceloop platform is $0 a month for up to 50K spans and 5 seats with 24 hours of retention, and Enterprise is custom
Teams that want vector database calls traced into the observability stack they already run
Hobby is free; Pro is $79 a month and Team is $799 a month; Enterprise is contact us
Teams that want to log retrieval calls by hand next to their LLM request logs
Pick by what you want
Best overall
LangSmith
Cheapest paid cloud plan
Comet Opik
Best free option
TruLens
Best retrieval-relevance evaluator
Arize Phoenix
Deepest RAG metric list
Ragas
Best for vector database tracing
OpenLLMetry
The ranking
1
LangSmith
Answrs VerdictTraces retrieval and documents four RAG evaluators in its own tutorial.
Price: Developer is $0 per seat a month with 1 seat; Plus is $39 per seat a month with unlimited seats; Enterprise is customRAG evaluators: Its Evaluate a RAG application tutorial defines four evaluators: correctness (response vs reference answer), relevance (response vs input), groundedness (response vs retrieved docs) and retrieval relevance (retrieved docs vs input)Retrieval tracing: The quickstart traces an assistant that calls a get_context function to retrieve context, with the tool call and the LLM call as nested spans in one traceBase traces: Up to 5k base traces a month on Developer and up to 10k on Plus, then pay as you goRetention: Base traces are kept 14 days and extended traces 180 days; the upgrade fee is not given on the pricing page
LangSmith Developer is $0 per seat a month with 1 seat, and Plus is $39 per seat a month with unlimited seats; Enterprise is custom. Its Evaluate a RAG application tutorial defines four evaluators: correctness, relevance, groundedness against retrieved docs and retrieval relevance. Its quickstart traces a get_context retrieval call and the LLM call as nested spans in one trace. Base traces are kept 14 days and extended traces 180 days, and the upgrade fee is not published.
Go ifTeams that want retrieval tracing and a worked RAG evaluation tutorial from one maker
Skip ifYou want a flat price instead of per-seat billing
Why #1 over #2: It documents both retrieval tracing and four RAG evaluators itself, while Langfuse reaches RAG scoring through Ragas.
2
Comet Opik
Answrs VerdictThe lowest paid cloud price here with retrieval tracing and a context metric.
Price: Open Source self-hosted is $0; Free Cloud is $0; Pro Cloud is $19 a month; Enterprise is customFree Cloud: 25k spans a month, up to 10 team members and 60-day data retentionPro Cloud: 100k spans a month and up to 50 team members, with customizable span limits and retentionRetrieval tracing: Every LLM call, every tool invocation and every retrieval step is captured as a trace you can inspect, search and analyzeRAG metric: Its ContextPrecision metric uses an LLM as a judge to evaluate the accuracy and relevance of a response based on provided context; gpt-4o is the default judge model
Comet Opik is $0 self-hosted or on Free Cloud, and Pro Cloud is $19 a month. Free Cloud has 25k spans a month, up to 10 team members and 60-day retention; Pro has 100k spans and up to 50 team members. Every retrieval step is captured as a trace, and its ContextPrecision metric uses an LLM as a judge, with gpt-4o as the default model.
Go ifTeams that want a self-hosted option, a low cloud price and a built-in context metric
Skip ifYou need unlimited team members below the Enterprise plan
Why #2 over #3: It has a published price and a self-hosted option, while TruLens lists no paid plan.
3
TruLens
Answrs VerdictFree and MIT-licensed, with RAG triad scoring and OpenTelemetry tracing together.
Price: Free and open source under the MIT license; no paid plan is listed on the pages we readRAG triad: The RAG use case is judged on Groundedness, Context Relevance and Answer Relevance, asking whether the answer is supported by what was retrievedTracing: Every function call, LLM generation, retrieval and tool invocation is captured as a structured OpenTelemetry span, exportable to Jaeger, Grafana Tempo, Datadog, New Relic or any OTLP backendBenchmark claim: Its site cites 0.93 context relevance NDCG@5 via AIMultiple (23 March 2026), ranking first of five tools on three of four metrics; this is TruLens reporting on itself
TruLens is free and open source under the MIT license, with no paid plan listed on the pages we read. It scores RAG on Groundedness, Context Relevance and Answer Relevance, and captures every function call, LLM generation, retrieval and tool invocation as an OpenTelemetry span that can go to any OTLP backend. Its site cites 0.93 context relevance NDCG@5 via AIMultiple, a claim TruLens reports about itself.
Go ifTeams that want free, OpenTelemetry-native tracing with RAG scoring built around the RAG triad
Skip ifYou want a hosted service with a published paid plan
Why #3 over #4: It pairs tracing with RAG triad scoring, while Ragas scores but does not trace.
4
Arize Phoenix
Answrs VerdictA dedicated Retrieval Relevance evaluator, but no published price.
Price: Not published on the Arize pricing page, which lists no Phoenix price or limitsRetrieval Relevance: A pre-built evaluator that determines whether the external information retrieved during a step is relevant to the request; the source can be a vector database or semantic search, a tool call or a web searchTracing: A trace captures model calls, retrieval, tool use and custom logic step by step; it is built on OpenTelemetryNotebooks: Example notebooks cover tracing, evals and RAG analysis; evaluator integrations include Ragas, Deepeval and Cleanlab
Arize Phoenix has no price or limits on the Arize pricing page. Its pre-built Retrieval Relevance evaluator checks whether information retrieved during a step is relevant to the request, whether it came from a vector database, a tool call or a web search. Traces capture model calls, retrieval and tool use over OpenTelemetry, and its notebooks include RAG analysis.
Go ifEngineers who want a retrieval-relevance evaluator and OpenTelemetry traces in one tool
Skip ifYou need a published price or limits before you start
Why #4 over #5: It has a dedicated retrieval evaluator, while Arize AX lists spans and retention but no RAG evaluator.
5
Ragas
Answrs VerdictThe deepest RAG metric list here, but it does not trace.
Price: Free open-source library under the Apache-2.0 license, installed with pip install ragasRAG metrics: The metrics list groups Context Precision, Context Recall, Context Entities Recall, Noise Sensitivity, Response Relevancy and Faithfulness under Retrieval Augmented GenerationTest data: Includes testset generation for RAG, which creates test datasets for you when you do not have one readyObservability: It is an evaluation library, not a tracing backend; its integrations list names Arize and LangSmith under Observability
Ragas is a free library under the Apache-2.0 license. Its metrics list groups Context Precision, Context Recall, Context Entities Recall, Noise Sensitivity, Response Relevancy and Faithfulness under Retrieval Augmented Generation, and it can generate RAG test sets. It is not a tracing backend; its integrations list names Arize and LangSmith for observability.
Go ifTeams that already trace elsewhere and want a library of RAG scoring metrics
Skip ifYou need a tool that records and stores traces itself
Why #5 over #6: It lists more RAG metrics than Langfuse, which relies on it for scoring.
6
Langfuse
Answrs VerdictFull price table and retrieval tracing; RAG scoring comes through Ragas.
Price: Hobby is free with 50k units a month; Core is $29, Pro is $199 and Enterprise is $2499 a month, each paid plan with 100k unitsExtra usage: Beyond the included units it is $8 per 100k units, lower with volumeData access: Hobby 30 days, Core 90 days, Pro 3 yearsRetrieval tracing: Each trace captures LLM calls, retrieval steps, tool executions and custom logic, with timing, inputs, outputs and metadataRAG evaluation: A Langfuse guide, Evaluation of RAG pipelines with Ragas, scores traces and spans with Ragas
Langfuse Hobby is free with 50k units a month; Core is $29, Pro is $199 and Enterprise is $2499 a month, each paid plan with 100k units and extra usage at $8 per 100k units. Data access is 30 days on Hobby, 90 days on Core and 3 years on Pro. Traces capture retrieval steps, and a guide scores RAG pipelines with Ragas.
Go ifTeams that want retrieval tracing with a full published price table and Ragas scoring
Skip ifYou want RAG metrics built into the product rather than added through Ragas
Why #6 over #7: It publishes a full price table, while Arize AX lists no RAG-specific guide beyond notebooks.
7
Arize AX
Answrs VerdictManaged tier with spans, ingestion and retention all listed.
Price: AX Free is $0 and AX Pro is $50 a month; AX Enterprise is customAX Free limits: 25k trace spans, 1 GB ingestion and 15 days retention a month, with unlimited usersAX Pro limits: 50k trace spans, 10 GB ingestion and 30 days retention a month, with unlimited usersRetrieval: Its docs say every LLM call, tool invocation and retrieval is captured as structured data, and list a Retriever span kindNotebooks: Its docs point to example notebooks for agents, RAG, voice, tracing and evals
Arize AX Free is $0 and AX Pro is $50 a month, with unlimited users on both. Free covers 25k trace spans, 1 GB ingestion and 15 days retention a month; Pro covers 50k spans, 10 GB and 30 days. Its docs say every retrieval is captured and list a Retriever span kind, and they point to RAG example notebooks.
Go ifTeams that want a managed platform with a flat $50 tier and unlimited users
Skip ifYou need more than 15 days of retention on the free tier
Why #7 over #8: It publishes limits and retention, while OpenLLMetry lists only 24 hours of retention.
8
OpenLLMetry
Answrs VerdictTraces seven vector databases, but lists no RAG metrics.
Price: OpenLLMetry is free under the Apache-2.0 license; the Traceloop platform is $0 a month for up to 50K spans and 5 seats with 24 hours of retention, and Enterprise is customVector DBs: Instrumentations cover the vector databases Chroma, LanceDB, Marqo, Milvus, Pinecone, Qdrant and WeaviateStandards: Built on OpenTelemetry, so it can connect to existing tools such as Datadog and HoneycombOwnership: The Traceloop pricing page shows a banner reading "Traceloop is joining Service now!" and gives no further detail there
OpenLLMetry is free under the Apache-2.0 license and instruments the vector databases Chroma, LanceDB, Marqo, Milvus, Pinecone, Qdrant and Weaviate. The Traceloop platform is $0 a month for up to 50K spans and 5 seats with 24 hours of retention. Its pricing page shows a banner reading "Traceloop is joining Service now!" with no further detail there.
Go ifTeams that want vector database calls traced into the observability stack they already run
Skip ifYou want built-in RAG scoring, which this page does not list
Why #8 over #9: It instruments vector databases directly, while Datadog only bills and lists retrieval spans.
9
Datadog LLM Observability
Answrs VerdictDoes not bill retrieval spans, but lists no RAG metrics.
Price: Free tier is $0 a month; Pro starts at $160 a month on an annual commitment, $200 month-to-month or $240 on-demandIncluded: Free has up to 40K LLM spans a month with 15-day trace retention; Pro includes 100K LLM spans a monthBilling: Billed per LLM span only, not tool spans, workflow spans or retrieval spans; extra spans are $3.50 per 10K on annual billingRetrieval: Its FAQ gives a retrieval step as an example of a separate span within the same trace as the reasoning and tool-use calls
Datadog LLM Observability is $0 on Free with up to 40K LLM spans a month and 15-day trace retention. Pro starts at $160 a month on an annual commitment, $200 month-to-month or $240 on-demand, with 100K LLM spans included and extra at $3.50 per 10K on annual billing. Only LLM spans are billed, not tool, workflow or retrieval spans.
Go ifTeams already on Datadog that want RAG traces next to their APM data
Skip ifYou want RAG-specific scoring, which the pricing page does not list
Why #9 over #10: It does not bill retrieval spans, while Helicone logs vector database calls by hand.
10
Helicone
Answrs VerdictVector DB calls are logged manually; no RAG metrics are listed.
Price: Hobby is free; Pro is $79 a month and Team is $799 a month; Enterprise is contact usHobby limits: 10,000 free requests a month, 1 GB storage, 1 seat and 1 organizationVector DB logging: Its docs show how to log vector database interactions to Helicone with cURL, including the search text, topK and database nameOwnership: The pricing page says Helicone is no longer part of Mintlify and gives no further details
Helicone Hobby is free with 10,000 requests a month, 1 GB storage, 1 seat and 1 organization. Pro is $79 a month and Team is $799 a month; Enterprise is contact us. Its docs show how to log vector database interactions with cURL, including the search text, topK and database name. The pricing page says Helicone is no longer part of Mintlify and gives no further details.
Go ifTeams that want to log retrieval calls by hand next to their LLM request logs
Skip ifYou want automatic retrieval tracing or RAG metrics
How we ranked these
We ranked AI observability tools for RAG pipelines by how many of three needs each maker's own pages document: tracing of retrieval steps, built-in RAG evaluation metrics, and a published price or license. Ties go to the tool with more RAG-specific material on its pages. Where a price is not published we say so, and benchmark claims are labelled as the maker's own. Facts are taken from each maker's own published information; check the official site before you buy.
Questions people ask
What is the best AI observability tool for RAG pipelines?
LangSmith ranks first: it traces the retrieval step and its own tutorial defines four RAG evaluators, including groundedness and retrieval relevance. Comet Opik and TruLens also document all three RAG needs we checked.
Which RAG observability tools are free?
TruLens is MIT-licensed, Ragas is Apache-2.0, and OpenLLMetry is Apache-2.0. Comet Opik is $0 self-hosted or on Free Cloud, and Langfuse Hobby is free with 50k units a month.
What is the cheapest paid plan?
Comet Opik Pro Cloud is listed at $19 a month, then Langfuse Core at $29 a month. LangSmith Plus is priced per seat at $39 a month and Arize AX Pro is $50 a month.
Do I need a separate tool to score retrieval quality?
Not always. LangSmith, Comet Opik, TruLens and Arize Phoenix document built-in evaluators for retrieval or context. Ragas is a metrics library that works alongside a tracing tool, and Langfuse documents scoring with Ragas.
Listed monthly price of the cheapest paid plan (LangSmith is per seat; Datadog is on an annual commitment) at a glance
Comet Opik19 USD
Langfuse29 USD
LangSmith39 USD
Arize AX50 USD
Helicone79 USD
Datadog LLM Observability160 USD
Listed monthly price of the cheapest paid plan (LangSmith is per seat; Datadog is on an annual commitment), as published by each maker. Picks without a published figure are left off.
