Free LLM Observability and Evaluation Tools
Which LLM tracing, monitoring and evaluation tools a startup can use for free today, how many traces or events the free plan covers, how long it keeps them, whether a card is needed and what the first paid plan costs, read from each tool's own page.
Free allowances read on each provider's own pages, all checked on or after . LLM observability tools change their free allowances often: confirm the terms on the tool's page before you route production traffic through one.
LLM observability tools a startup can use for free today include Langfuse (50K units a month), Opik (Comet) (25K spans a month, free), Helicone (10,000 requests, free), HoneyHive (10K events a month, free), and LangSmith (5k base traces a month). Each of the 13 free plans below links to the tool's page that states it, with its main limit, how long data is kept, whether a card is needed and what the first paid plan costs.
Once an AI feature is live, you need to see every model call: the prompt, the answer, the cost, the latency and where an agent went wrong. LLM observability and evaluation tools record that, and almost all of them have a free plan.
The headline rarely tells you how far it goes. A free plan can cap traces, spans or requests a month, allow one seat, or keep data for only a few days, which decides whether you can still debug last week's bad answer. Each tool below shows what is free, its main limit, how long data is kept, whether a card is needed and what the first paid plan costs, quoted from the tool's own page with the date we read it.
Which tools we picked and the order they appear in are our editorial choices; the terms are the tools'. Some of these tools pay us a referral commission when someone signs up through our link: those links are labeled, and they play no part in which tools are listed or where.
LLM tracing and monitoring with a free plan
Traces, costs and latency for every model call, with a free monthly allowance.
- 1
Langfuse
Teams that want the most trace units on a free plan
Langfuse's Hobby plan is free, with no credit card required, and includes 50k units a month, 30 days of data access and 2 users. The first paid plan, Core, is $29 a month.
- What's free
- 50K units a month (source: langfuse.com)
- Data history
- 30 days (source: langfuse.com)
- Payment card
- No card needed (source: langfuse.com)
- First paid plan
- Core: $29 a month (source: langfuse.com)
Start free at LangfuseTerms read on langfuse.com on Langfuse: the free allowance and how to start Langfuse for Startups: what startups get - 2
Helicone
Trying an LLM gateway and request logs with one seat
Helicone's Hobby plan gives 10,000 free requests, with 1 seat, 1 organization and 7 days of retention. Its Pro plan, the first paid tier, is $79 per month.
- What's free
- 10,000 requests, free (source: helicone.ai)
- Data history
- 7 days (source: helicone.ai)
- First paid plan
- Pro: $79 a month (source: helicone.ai)
Start free at HeliconeTerms read on helicone.ai on Helicone: the free allowance and how to start Helicone Startup Discount: what startups get - 3
LangSmith
Solo builders on LangChain who want traces and evals
LangSmith's Developer plan covers 1 seat with up to 5k base traces a month, then pay-as-you-go. Base traces are kept for 14 days. The Plus plan is $39 per seat a month.
- Main limit
- 1 seat (free) (source: langchain.com)
- Data history
- 14 days for base traces (source: langchain.com)
- First paid plan
- Plus: $39 a seat a month (source: langchain.com)
Start free at LangChainTerms read on langchain.com on LangSmith: the free allowance and how to start LangSmith for Startups: what startups get - 4
Portkey
Testing a gateway and its logs before production
Portkey's Developer plan is free forever, with 10k recorded logs a month, 3 days of log retention and 3 prompt templates. Production is $49 a month.
- Main limit
- 3 prompt templates (source: portkey.ai)
- Data history
- 3 days for logs (source: portkey.ai)
- First paid plan
- Production: $49 a month (source: portkey.ai)
- 5
Langtrace
One developer tracing spans and running evals
Langtrace's Starter plan is free forever for 1 user, with up to 10K spans a month, prompt management and evaluations. Growth is $39 per user a month.
- Main limit
- 1 user (source: docs.langtrace.ai)
- First paid plan
- Growth: $39 a user a month (source: docs.langtrace.ai)
Start free at LangtraceTerms read on docs.langtrace.ai on Langtrace: the free allowance and how to start - 6
Laminar
Small projects that want 1 GB of trace data
Laminar's free tier gives 1 GB of data with no overage, 7 days of data access, 1 project and 1 seat. Its Starter plan is $30 a month.
- What's free
- 1 GB data, no overage (source: laminar.sh)
- Main limit
- 1 project, 1 seat (source: laminar.sh)
- Data history
- 7 days of data access (source: laminar.sh)
- First paid plan
- Starter: $30 a month (source: laminar.sh)
- 7
PromptLayer
Solo prompt work with a free request allowance
PromptLayer's Free plan allows 2.5k requests a month, with 1 workspace and 250 eval cell executions a month. Its Pro plan is $49 per month.
- First paid plan
- Pro: $49 a month (source: promptlayer.com)
Start free at PromptLayerTerms read on promptlayer.com on PromptLayer: the free allowance and how to start
LLM evaluation platforms with a free plan
Datasets, experiments and scoring for prompts and agents, with a free plan to start.
- 1
Opik (Comet)
Solo developers wanting 60 days of trace history
Comet's Free Cloud plan allows up to 10 team members, 25k spans per month and 60-day data retention. Pro Cloud is $19 per month.
- What's free
- 25K spans a month, free (source: comet.com)
- Data history
- 60 days (source: comet.com)
- First paid plan
- Pro Cloud: $19 a month (source: comet.com)
- 2
HoneyHive
Small teams running evals with up to 5 users
HoneyHive's Developer plan is free, with 10,000 events per month, up to 5 users and 30-day data retention. No credit card required. Enterprise pricing is custom.
- Main limit
- Up to 5 users (source: honeyhive.ai)
- Data history
- 30 days (source: honeyhive.ai)
- Payment card
- No card needed (source: honeyhive.ai)
- First paid plan
- Enterprise: custom pricing (source: honeyhive.ai)
- 3
Braintrust
Whole teams running evals on 1 GB of data a month
Braintrust's Starter plan includes 1 GB of processed data a month and free usage for traces, evals and your whole team. Retention is 14 days. Pro is $249 a month.
- Data history
- 14 days (source: braintrust.dev)
- Payment card
- No card needed (source: braintrust.dev)
- First paid plan
- Pro: $249 a month (source: braintrust.dev)
Start free at BraintrustTerms read on braintrust.dev on Braintrust: the free allowance and how to start Braintrust for Startups: what startups get - 4
Arize AX
Builders starting with 25K trace spans a month
Arize AX Free includes 25k spans per month and 10 issues per month, with 15 days of retention. No credit card required. AX Pro is $50 per month.
- What's free
- 25K spans a month, free (source: arize.com)
- Main limit
- 10 issues a month (source: arize.com)
- Data history
- 15 days (source: arize.com)
- Payment card
- No card needed (source: arize.com)
- First paid plan
- AX Pro: $50 a month (source: arize.com)
Start free at Arize AITerms read on arize.com on Arize AX: the free allowance and how to start Arize for Startups: what startups get - 5
Agenta
Teams testing agents with daily free credits
Agenta's Hobby plan has 75 free credits a day, on up to 10 days a month, with 1 project and 2 team members. Sign up in seconds, no credit card required. Starter is $29 a month.
- Payment card
- No card needed (source: agenta.ai)
- First paid plan
- Starter: $29 a month (source: agenta.ai)
- 6
Weights & Biases (Weave)
Builders tracing with 1 GB of Weave data a month
The free Weave plan is designed for personal development of AI applications and models, with 1 GB of Weave data ingestion a month. Pro starts at $60 a month, billed monthly.
- First paid plan
- Pro: from $60 a month (source: wandb.ai)
AI tooling startup programs
Programs from AI tooling companies that give startups credits or free months on paid plans.
Also useful for building with AI models
Referral links, picked for fit and ordered by fit (70%) and what a signup earns us (30%), at no cost to you. They never change this page's ranking.
How this comparison is built
The list covers LLM tracing, monitoring and evaluation tools a founder can use for free today without applying to a program. The order and the "best for" notes are our editorial reading of each tool's terms. Every term comes from the tool's own pricing or help page on the date shown, never from a third-party list; follow each link for the full conditions. A cap on traces or events, or a short data history, can matter more than the headline, so the comparison quotes them wherever the tool states them. Some of these tools pay StartupPerks a referral commission, and their links are labeled as referral links; that decides neither whether nor where a tool appears, and no tool pays for a placement on this page.
Read the full methodologyCommon questions
What is the best free LLM observability tool?
It depends on volume and team size. By the terms each tool states, Langfuse's free plan includes 50K units a month for 2 users, Opik 25K spans a month for up to 10 team members, Arize AX 25K spans a month, Langtrace 10K spans a month and Helicone 10,000 requests.
Is LangSmith free?
Yes, for one seat: LangSmith's free plan includes 5k base traces a month, kept for 14 days. Plus costs $39 a seat a month.
Is Langfuse free?
Yes. Langfuse's free plan includes 50K units a month for 2 users, with 30 days of data and no card needed. Core costs $29 a month.
How long do free plans keep LLM traces?
From 3 days to 60, by each tool's own terms: Portkey keeps logs for 3 days, Helicone and Laminar for 7, LangSmith and Braintrust for 14, Arize AX for 15, Langfuse and HoneyHive for 30, and Opik for 60.
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