LLM observability platforms bill four different ways - per seat with metered units (LangSmith), per unit of trace volume (Langfuse), per scored output (Braintrust), per span and ingestion volume (Arize AX), or per request (Helicone). We compare all five on what a free tier actually gives you, where the bill jumps, and how long your data is kept.
5 LLM Observability tools are tracked in this index. 5 of them ship a free plan (LangSmith, Langfuse, Braintrust, Arize AX, Helicone). The lowest published entry price in the category is $29/mo (Core) (Langfuse). Across the 5 scored LLM Observability entries, the index average is 4.1/5, led by LangSmith at 4.4/5. Most common tags on this page: Evaluation (3 tools), Observability (3 tools), Agent tracing (1 tool), BYOK-friendly (1 tool). Pricing figures behind these entries were last checked between 2026-10-03; every tool page carries its own check date.
Browse every head-to-head in the LLM Observability comparison hub →
The full set of LLM Observability entries, with the plan shape each vendor actually publishes:
Every price point above is copied from the vendor's own pricing page and carries the date it was checked on the individual tool page — we do not fill gaps from third-party roundups. Where a figure could not be verified against an official source, the tool page says so instead of guessing.
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.
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.
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.
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.
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.
When you compare LLM Observability tools, the fields that decide the outcome are the ones this index actually stores: whether a free plan exists and what it limits, the published entry price and how it bills (per seat, per month, per workspace), what the trial covers, which of the six index dimensions the tool scores on, when each figure was last checked against the official page, and which alternatives sit in the same category. Each tool page prints those fields with its own verification date, the LLM Observability comparison pages put two products side by side on the same fields, and the list pages rank the category against the rest of the index — so you can move from a shortlist to a decision without opening a vendor's sales page.
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5 tools are tracked here, 5 of them with a free plan, and paid entry pricing starts at $29/mo (Core) (Langfuse). LLM observability platforms bill four different ways - per seat with metered units (LangSmith), per unit of trace volume (Langfuse), per scored output (Braintrust), per span and ingestion volume (Arize AX), or per request (Helicone). We compare all five on what a free tier actually gives you, where the bill jumps, and how long your data is kept
LangSmith, Langfuse, Braintrust, Arize AX, Helicone list a free plan in this index; LangSmith paid plans start at $39/seat/mo (Plus).
Langfuse has the lowest published entry price on this page at $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). Langfuse also lists a free plan.
Every price point above is copied from the vendor's own pricing page and carries the date it was checked on the individual tool page — we do not fill gaps from third-party roundups. Where a figure could not be verified against an official source, the tool page says so instead of guessing.
LangSmith leads this category at 4.4/5 — 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. The category average across 5 scored entries is 4.1/5.