📖 The 6 Best Free LLM Observability Tools Compared

If you build with LLMs in 2026, you need observability. Without it, you are flying blind — unable to trace why a response degraded, measure whether a prompt change improved quality, or catch regressions before they hit users.

The good news: the free tiers of the leading LLM observability platforms have never been more generous. Langfuse gives you 50k observations/month for nothing. Portkey hands you 1 million spans. Braintrust's Starter plan is genuinely free for individuals. And the open-source options (Langfuse, Comet Opik, LangWatch) let you self-host at zero platform cost.

The bad news: picking the right one is overwhelming. Each platform takes a different philosophical approach — some prioritize tracing depth, others eval workflow, others the AI gateway angle.

We tested all six on the same criteria: Ease of Setup, Features, Performance, Documentation, and Community Support. Here is the full breakdown.

TL;DR: Langfuse (8.4/10) is the best overall — MIT license, billion-scale ClickHouse architecture, and the most complete feature set. Portkey (7.8/10) wins on free tier volume and doubles as an AI gateway. Braintrust (7.4/10) has the best CI/CD eval pipeline. Your choice depends on whether you need self-hosting, eval rigor, or a combined gateway + observability stack.

📊 Quick Comparison Table

Sources: Langfuse pricing [1], Langtrace pricing [2], LangWatch pricing [3], Comet Opik pricing [4], Braintrust pricing [5], Portkey pricing [6]. All data verified June 2026.

🏆 Tool-by-Tool Breakdown

1. Langfuse — 8.4/10 (Best Overall)

Dimensions: Ease 8 | Features 9 | Performance 8 | Docs 9 | Support 8

Langfuse is the open-source LLM engineering platform that keeps winning. It combines tracing, evaluation, prompt management, experiments, and a playground into one MIT-licensed platform. Built on ClickHouse for analytical speed and Redis for async ingestion, it handles billions of observations per month for 19 Fortune 50 companies [1].

The free Hobby tier includes 50k observations/month with unlimited team members — no credit card needed. The Core plan at $29/mo bumps to 100k observations with 90-day retention. Self-hosting is completely free and fully featured, with no enterprise edition gating.

Best for: Teams that want full data ownership, self-hosting, and the most complete feature set. The 80+ framework integrations (LangChain, CrewAI, Pydantic AI, Vercel AI SDK, and more) make it the most broadly compatible option [7].

2. Portkey — 7.8/10 (Best Free Tier Volume)

Dimensions: Ease 9 | Features 8 | Performance 7 | Docs 8 | Support 7

Portkey takes a unique approach — it is both an AI gateway and an observability platform. This means you get routing, fallbacks, load balancing, and retries alongside tracing and evaluation. The free tier offers 1 million spans per month plus 10k eval scores — the highest raw volume of any tool here [6].

Setup is dead simple: you point your LLM calls through Portkey's proxy and observability works automatically. Pro at $249/mo unlocks unlimited spans and scores. Portkey is cloud-only with no self-hosting option.

Best for: Teams that want observability + gateway features in one stack and need high-volume free usage. The 9/10 ease score reflects how quickly you can get production traces flowing.

<h3. LangWatch — 7.6/10 (Best for DSPy Optimization)

Dimensions: Ease 7 | Features 8 | Performance 7 | Docs 8 | Support 8

LangWatch differentiates itself with deep DSPy optimization integration — it can automatically optimize your DSPy programs based on evaluation results. It also offers guardrails (real-time content filtering) which most competitors lack [3].

The free Developer plan gives access to core features. Paid plans start at €59/month and include unlimited evaluations, DSPy optimization, and enterprise security. Self-hosting is available and free.

Best for: Teams using DSPy for prompt optimization who want guardrails alongside observability. The real-time content filtering is a genuine differentiator.

4. Comet Opik — 7.5/10 (Best Apache 2.0 Alternative)

Dimensions: Ease 7 | Features 8 | Performance 7 | Docs 7 | Support 8

Comet Opik is the Apache 2.0 open-source LLM evaluation and observability platform from the Comet ML team. It provides tracing, automated evaluations via LLM-as-a-judge, and deep integration with the Comet experiment tracking ecosystem [4].

The free cloud tier includes 5k traces/month. The full feature set is available in the open-source self-hosted version. Paid plans at $39/seat/month unlock higher limits and team features. Comet's existing user base makes this a natural choice for ML teams already in the Comet ecosystem.

Best for: ML teams already using Comet for experiment tracking who want a unified observability layer. The Apache 2.0 license is more permissive for some enterprise use cases than MIT.

5. Braintrust — 7.4/10 (Best CI/CD Eval Pipeline)

Dimensions: Ease 8 | Features 7 | Performance 7 | Docs 8 | Support 7

Braintrust is built around an eval-first philosophy: design a prompt, test systematically, ship to production, monitor, and convert production failures into permanent test cases with one click. The trace-to-test pipeline is the most mature implementation of this workflow in any platform [5].

The free Starter plan includes 1 GB of processed data and 10K scores with 14-day retention. Pro at $249/mo bumps to 5 GB, 50K scores, and 30-day retention. Self-hosting is enterprise-only.

Best for: Teams running agentic systems who need rigorous CI/CD eval gates. The ability to turn any production failure into a permanent regression test is a superpower.

6. Langtrace — 7.2/10 (Simplest Onboarding)

Dimensions: Ease 8 | Features 6 | Performance 7 | Docs 7 | Support 7

Langtrace focuses on simplicity — OpenTelemetry-native tracing with a clean UI and minimal configuration. It is the easiest platform to get started with if all you need is basic LLM call tracing and cost tracking [2].

The free tier includes a limited number of spans per month. Paid plans scale with usage. Feature depth lags significantly behind Langfuse and Portkey — there is no prompt management or experiment workflow.

Best for: Solo developers and small teams who want quick LLM tracing without configuration overhead. The simplicity is a feature, but you will outgrow it fast.

🥇 Winners by Category

Easiest to Set Up: Portkey (9/10)

Portkey's gateway proxy approach means you add one line of configuration and traces flow automatically. No SDK instrumentation per framework. Langfuse and Braintrust are close at 8/10 but require SDK setup per integration.

Most Features: Langfuse (9/10)

Nothing else comes close. Tracing, eval, prompt management, experiments, playground, human annotation — all in one platform with 80+ integrations. Portkey (8/10) and LangWatch (8/10) tie for second.

Best Performance: Langfuse (8/10)

ClickHouse + Redis + S3 architecture scales to 10+ billion observations/month. Sub-second trace queries at scale. All other platforms use standard Postgres or similar and top out at 7/10.

Best Documentation: Langfuse (9/10)

Extensive docs with cookbooks, video guides, API references, and an excellent agent SKILL.md. Braintrust (8/10) and Portkey (8/10) are close but less complete.

Best Free Tier: Portkey

1 million spans/month free is hard to beat. Langfuse's 50k observations is more restrictive but offers unlimited team members. For solo devs or small teams, Portkey's volume is unmatched.

Best for Self-Hosting: Langfuse

Full MIT license, no feature gating, Docker Compose and Kubernetes support, Terraform templates for AWS/GCP/Azure. Comet Opik is a close second with Apache 2.0 but a smaller community.

Best for CI/CD Eval: Braintrust

The trace-to-test pipeline with one-click regression gating is genuinely elegant. Langfuse offers eval via SDK but Braintrust's workflow is more refined and battle-tested.

💡 Which One Should You Choose?

Your Priority	Pick This Tool
Best overall, self-hostable	Langfuse (8.4/10)
Highest free volume (1M spans)	Portkey (7.8/10)
CI/CD eval pipeline	Braintrust (7.4/10)
DSPy optimization + guardrails	LangWatch (7.6/10)
Apache 2.0 + Comet ecosystem	Comet Opik (7.5/10)
Simplest onboarding	Langtrace (7.2/10)
AI gateway + observability	Portkey (7.8/10)

💰 Pricing at a Glance

Pricing sources: Langfuse [1], Langtrace [2], LangWatch [3], Comet Opik [4], Braintrust [5], Portkey [6]. All information verified June 2026.

🔍 Methodology

We evaluated each tool across five dimensions on a 1-10 scale:

• Ease: How quickly can a beginner set up tracing and see their first results? Minutes to first trace, SDK ergonomics, configuration overhead.
• Features: Breadth and depth of capabilities — tracing, eval, prompt management, playground, experiments, guardrails, CI/CD integration.
• Performance: Trace ingestion speed, query latency at scale, uptime, architecture (ClickHouse vs Postgres).
• Docs: Quality of documentation — getting started guides, cookbooks, API reference, code examples, video content.
• Support: Community responsiveness (GitHub, Discord, Slack), commercial support options, frequency of releases and updates.

Scores reflect free-tier capabilities as of June 2026. Paid tiers may unlock additional features that improve the score for paying users.

Note: ToolBrain is not affiliated with any of these tools. We are readers too — every link, score, and comparison is researched and fact-checked.

❓ Frequently Asked Questions

What is the best free LLM observability tool in 2026?

Langfuse is the best overall with a 50k observations/month free tier, full MIT open-source license, and the most complete feature set. See the comparison above for use-case-specific recommendations.

Which tool has the most generous free tier by volume?

Portkey offers 1 million spans per month free — significantly more than any other platform. Langfuse offers 50k observations with unlimited team members, which is better for team collaboration.

Are any of these tools fully open source?

Yes — Langfuse (MIT), LangWatch (free self-host), and Comet Opik (Apache 2.0) are fully open source. Braintrust's core is open source but self-hosting requires Enterprise. Langtrace and Portkey are cloud-only with proprietary licenses.

Which is best for production workloads?

Langfuse has the most production-proven infrastructure (10+ billion observations/month, 19 Fortune 50 customers). Portkey is also production-ready with enterprise features. Braintrust is production-strong for eval workflows specifically.

🔚 Final Verdict

Langfuse takes the crown at 8.4/10 as the best all-around free LLM observability platform in 2026. The MIT license, billion-scale ClickHouse architecture, and unified tracing-eval-prompt workflow make it the default choice for teams that want full data ownership and unlimited team members.

But there is no single winner for every use case:

• Portkey leads on free tier volume (1M spans) and doubles as an AI gateway
• Braintrust wins on CI/CD eval workflow maturity
• LangWatch is strongest for DSPy optimization with built-in guardrails
• Comet Opik is the best Apache 2.0 alternative for Comet ecosystem teams
• Langtrace offers the simplest onboarding for beginners

The good news: all six are free to start. Try two or three — the best way to choose is to instrument a small project and see which workflow clicks for your team.

References

1. Langfuse Pricing — Free tier: 50k obs/mo, unlimited users. Self-hosted: fully MIT-licensed.
2. Langtrace Pricing — Free tier with limited spans per month. Usage-based paid plans.
3. LangWatch Pricing — Free Developer plan. Paid from €59/mo with unlimited evaluations.
4. Comet Opik Pricing — Free tier: 5k traces/mo. Apache 2.0 open-source self-hosted option.
5. Braintrust Pricing — Free Starter: 1 GB data, 10K scores, 14-day retention. Pro: $249/mo.
6. Portkey Pricing — Free: 1M spans, 10k scores. Pro: $249/mo for unlimited spans.
7. Langfuse Homepage — 23,000+ GitHub stars, 5,000+ Discord members, 19 Fortune 50 customers.
8. Langfuse Documentation — OpenTelemetry-native instrumentation with 80+ framework integrations.
9. Braintrust Docs — Plans and Limits — Starter: unlimited users, projects, and datasets.
10. Comet Opik Product Page — Open-source LLM evaluation and observability, Apache 2.0.

📊 See all LLM tool comparisons →

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