Best LLM Observability Tools 2026: LangSmith vs Langfuse vs Braintrust vs Arize AX vs Helicone
Four of five have a genuine free tier, and none of them charge for the same thing: LangSmith (4.4/5) sells seats plus units, Langfuse (4.3/5) sells trace units and self-hosting, Braintrust (4.2/5) sells scores, Arize AX (4.0/5) sells spans at a $50 entry, Helicone (3.8/5) sells requests.
| Tool | Rating | Pricing | Best for |
|---|---|---|---|
| LangSmith Best overall Best for teams | 4.4/5 | Free $39/seat/mo (Plus) | LangSmith is the observability and evaluation platform from the LangChain team: $0/seat wi… |
| Langfuse Best free | 4.3/5 | Free $29/mo (Core) | Langfuse is the open-source-first LLM observability platform: free Hobby with 50K units a … |
| Braintrust | 4.2/5 | Free $249/mo (Pro) | Braintrust is the observability and eval platform with the most explicit score pricing in … |
| Arize AX | 4.0/5 | Free $50/mo (AX Pro) | Arize AX is the cheapest paid step in the cluster at $50/mo, with a $0 Free tier (25K span… |
| Helicone | 3.8/5 | Free $79/mo (Pro) | Helicone is the request-level observability and gateway layer priced per request: Hobby fr… |
Bottom line: the decision here is which unit you want to pay in. LangSmith (4.4/5) has the widest platform - tracing, evaluation, deployment, engine - at $39/seat plus $1.00 per LangChain Standard Unit, and is the pick for teams whose agents are complex enough that observability is not a side concern. Langfuse (4.3/5) is the value and open-source answer: free at 50K units, $29 for the first paid step with unlimited users, and a self-hosted option at every tier. Braintrust (4.2/5) is the one that publishes its score economics outright, but the step from free to $249 is the sharpest in the set. Arize AX (4.0/5) never charges for seats or evals and enters at $50, with the free open-source Phoenix for fully local work. Helicone (3.8/5) is a one-line proxy log with a gateway attached, and is now part of Mintlify. Prices verified from each vendor page on 2026-10-03.
Pricing and details
LangSmith · 4.4/5
Free plan available · $39/seat/mo (Plus)
Trace volume is metered in LangChain Standard Units (LSU) at $1.00/LSU on top of the seat fee; base traces carry 14-day retention, extended traces 180 days, and retention auto-upgrades can raise your bill
No annual pricing published on the LangSmith pricing page
LangSmith is the observability and evaluation platform from the LangChain team: $0/seat with 5K base traces a month, Plus at $39/seat with 10K, then pay-as-you-go at $1.00 per LangChain Standard Unit.
Score breakdown
Pros
- Widest platform in the cluster - tracing, monitoring, evaluation, prompt hub, deployment, sandboxes and an autonomous debugging engine under one login
- The only vendor that publishes its metering unit (LSU at $1.00) and per-resource rates, so a bill can be estimated before you commit
- 14-day base and 180-day extended retention are documented explicitly, including which actions upgrade a trace and which do not
- Native integrations for the major agent frameworks plus OpenTelemetry SDKs for Python, TypeScript, Go and Java
Cons
- Retention auto-upgrades are the bill trap: online evaluators and automation rules push matching traces to the pricier extended tier unless you opt out per evaluator
- Extended retention for SaaS tops out at 180 days as of 2026-09-14, so long-horizon analysis has to go to Enterprise customization
- Plus is $39/seat with unlimited seats, which punishes a wide read-only audience paying for observability they do not act on
Pricing verified 2026-10-03
Langfuse · 4.3/5
Free plan available · $29/mo (Core)
Usage is billed in units (100K units included on paid tiers, then $8 per additional 100K, lower at volume); a separate self-hosted pricing page exists for on-prem deployments
No published annual rate; Pro carries an optional Teams add-on at $300/mo for SSO, SSO enforcement and fine-grained RBAC
Langfuse is the open-source-first LLM observability platform: free Hobby with 50K units a month, Core at $29/mo for 100K units and 90-day retention, Pro at $199/mo with three-year retention, Enterprise at $2,499/mo.
Score breakdown
Pros
- A real free tier with no credit card: 50K units a month, all platform features, 30 days of data access and 2 users
- Core at $29/mo is by far the cheapest paid step in the cluster, with unlimited users on every paid tier
- Cloud and self-hosted deployment from the same product, so privacy-sensitive teams have a real path instead of a sales call
- Published discounts for startups, research and students, plus a documented open-source project track
Cons
- Core retains data for 90 days only - three-year retention needs the $199 Pro plan
- No deployment runtime or autonomous debugging engine, so it covers tracing and evaluation but not the agent platform around them
- The optional Teams add-on for SSO and fine-grained RBAC is another $300/mo on top of Pro
Pricing verified 2026-10-03
Braintrust · 4.2/5
Free plan available · $249/mo (Pro)
Scored outputs are the billing unit (LLM-as-a-judge, autoevals, custom scorers) alongside processed data and model credits; retention beyond 30 days is billed at $0.50/GB/mo up to 180 days on Pro
No published annual rate; Pro offers 6-12 months free for qualifying startups
Braintrust is the observability and eval platform with the most explicit score pricing in the cluster: Starter is $0 with 10K scores a month, Pro jumps to $249/mo with 50K scores plus cheaper per-1K rates.
Score breakdown
Pros
- The most explicit pricing in the cluster: scores are named as the billing unit with rates ($2.50/1K on Starter, $1.50/1K on Pro), processed data and model credits are listed line by line
- Starter is genuinely free with unlimited users, projects, datasets, playgrounds and experiments - no card required
- Retention is priced rather than hidden: 14 days included on Starter, 30 on Pro, then $0.50/GB/mo up to 180 days
- 6-12 months free for qualifying startups, and an open research program with published foundations
Cons
- The Starter-to-Pro step is $0 to $249/mo, so a team that crosses 10K scored outputs a month faces a large step rather than a gradual bill
- Custom charts, environments, priority support and RBAC are Pro-only, so the free tier is genuinely basic
- No S3 data export or custom retention policies until Enterprise
Pricing verified 2026-10-03
Arize AX · 4.0/5
Free plan available · $50/mo (AX Pro)
Billed on signals, spans, ingestion volume and retention rather than seats - users and evals are unlimited on every tier; self-hosted deployment is Enterprise-only, while the open-source Phoenix platform is free and local
No published annual rate; a separate startup pricing track exists on the pricing page
Arize AX is the cheapest paid step in the cluster at $50/mo, with a $0 Free tier (25K spans, 1 GB, 15-day retention) and a free open-source sibling in Arize Phoenix for fully local tracing.
Score breakdown
Pros
- Unlimited users and unlimited evaluations on every tier, including the free one - the only cluster member that never charges for seats
- $50/mo is the cheapest paid step in the set, undercutting Braintrust Pro by 5x
- Arize Phoenix is a genuinely free, open-source, local-first platform for tracing and evaluation with no account required
- Session-level and multi-modal tracing (image, voice, PDF), agent trajectory visualizations and online/offline evals are unlimited on all tiers
Cons
- The free tier is narrow - 10 signals a month and 25K spans, so production volume will not fit
- Self-hosted deployment is Enterprise-only; the free local option is the separate Phoenix project, not AX itself
- SOC 2 Type II, SSO, audit logs, HIPAA and data-region choice start at Enterprise
Pricing verified 2026-10-03
Helicone · 3.8/5
Free plan available · $79/mo (Pro)
Requests are the billing unit and usage-based pricing applies on top of every paid tier; storage beyond 1 GB is usage-billed, and Helicone announced it has joined Mintlify
No published annual rate; published discounts are 50% off year one for startups under 2 years old and under $5M raised, org-size-based non-profit discounts, a $100 first-year credit for open-source companies and free plans for students
Helicone is the request-level observability and gateway layer priced per request: Hobby free with 10,000 requests a month, Pro at $79/mo, Team at $799/mo, and usage-based pricing on top.
Score breakdown
Pros
- The easiest adoption story in the cluster - a one-line integration, the clearest interface of the five, and no framework lock-in since it sits at the request layer
- Straightforward request-based pricing with a published calculator: 10K free requests, then usage-based billing on every paid tier
- Caching, rate limits, automatic fallbacks and a gateway ship in the same product, so observability and routing are one purchase
- Real discount programs: 50% off year one for startups under 2 years old and under $5M raised, org-size non-profit discounts, a $100 credit for open-source companies, free for students
Cons
- Narrowest scope: its own pricing page rates its tracing, UI, experiments and evaluation as limited or average against the other four
- 7-day retention on Hobby and only 1 month on Pro, with 3 months on the $799 Team plan
- Ingest ceilings are low by comparison - 10 logs/min on Hobby against 1,000 on Pro and 30,000 on Enterprise
Pricing verified 2026-10-03
Frequently asked questions
How many LLM Observability tools are compared here?
This page compares 5 LLM Observability tools, with LangSmith as our top-rated pick. Pricing was last re-checked on 2026-10-03.
Which LLM Observability tool has the best free plan?
Langfuse is our free-tier pick among the tools compared.