Promptfoo vs LangSmith: Which is Better in 2026?
Choosing between Promptfoo and LangSmith comes down to understanding what each tool does best. This comparison breaks down the key differences so you can make an informed decision based on your specific needs, not marketing claims.
Bottom line: Promptfoo wins this matchup. UiPath is our overall AI Agents pick. Lucid Train is our free AI Agents pick. Pick LangSmith if you need AI agents.
Short on time? Here's the quick answer
Based on published vendor pricing and features and on public review data, here's who should pick what:
Promptfoo
Build secure AI applications with AI security testing integrated into your development workflow.
Best for you if:
- • You want LLM eval framework
LangSmith
Debug, monitor, and optimize your LLM applications and AI agents with comprehensive observability.
Best for you if:
- • You want provides deep visibility into non-deterministic LLM behavior
| At a Glance | LangSmith | |
|---|---|---|
Starts at | Free Free plan | Free Free plan |
Category | Security Testing & QA | AI Agents Developer Tools |
Rating | n/a | n/a |
Free plan | Yes | Yes |
Watch out for | No public overage pricing for Cloud | Traces over the included 5k/10k are pay-as-you-go. Seats are only the floor. |
Choose Promptfoo or LangSmith?
Choose Promptfoo if
- You want LLM eval framework
- You want open source
- You work in security, not AI agents
Choose LangSmith if
- You want provides deep visibility into non-deterministic LLM behavior
- You want helps improve application performance and response quality
- Budget matters (Free vs Free)
- You work in AI agents, not security
In-Depth Analysis
Promptfoo
Build secure AI applications with AI security testing integrated into your development workflow.
The pricing for Promptfoo is very generous, especially with a robust free tier offering unlimited local evals and all features.
Watch out
No public overage pricing for Cloud
Strengths
- Pro: LLM eval framework
- Pro: Open source
- Pro: Good for testing prompts
- Pro: Active development
- Pro: Good documentation
Weaknesses
- Con: Learning curve
- Con: CLI focused
- Con: Newer tool
- Con: Limited features
- Con: Still maturing
Key features
LangSmith
Debug, monitor, and optimize your LLM applications and AI agents with comprehensive observability.
LangSmith Developer is $0 for one seat and 5,000 base traces/month.
Watch out
Traces over the included 5k/10k are pay-as-you-go. Seats are only the floor.
Strengths
- Pro: Provides deep visibility into non-deterministic LLM behavior
- Pro: Helps improve application performance and response quality
- Pro: Offers comprehensive monitoring and alerting capabilities
- Pro: Identifies systemic issues and user needs automatically
- Pro: Flexible integration with various frameworks and OTel
Weaknesses
- Con: Specific pricing details require visiting a separate page
- Con: Self-hosting is only available on the enterprise plan
- Con: Requires some setup (e.g., environment variables) to get started
Key features
Pricing: Promptfoo vs LangSmith
| Plan | Promptfoo | LangSmith |
|---|---|---|
| Tier 1 | Free Free | Free Developer |
| Tier 2 | $50 month Cloud | $39 month Plus |
| Tier 3 | custom Enterprise | Custom Enterprise |
Pricing verified from each vendor's public pricing page. Compare in detail on Promptfoo pricing and LangSmith pricing.
Key Takeaways
Promptfoo
- Free tier available
- Our pick for this comparison
LangSmith
- Better fit for AI agents
The Bottom Line
Promptfoo wins this matchup. UiPath is our overall AI Agents pick. Lucid Train is our free AI Agents pick.
Frequently Asked Questions
Is Promptfoo or LangSmith better in 2026?
Promptfoo wins this matchup. UiPath is our overall AI Agents pick. Lucid Train is our free AI Agents pick. Pick Promptfoo for security workflows (main strength: LLM eval framework). Pick LangSmith for AI agents workflows (main strength: provides deep visibility into non-deterministic LLM behavior).
What are Promptfoo and LangSmith used for?
Promptfoo: Build secure AI applications with AI security testing integrated into your development workflow. LangSmith: Debug, monitor, and optimize your LLM applications and AI agents with comprehensive observability.
What does Promptfoo cost vs LangSmith?
Promptfoo's paid plans start at Free (Cloud). LangSmith's paid plans start at Free (Plus).
What's the main difference between Promptfoo and LangSmith?
Promptfoo's main strength: LLM eval framework. LangSmith's main strength: provides deep visibility into non-deterministic LLM behavior.