LangSmith vs promptfoo
Which should you use? A side-by-side look at what each one does, who it suits, what it costs, how hard it is to set up, and where each falls short.
AI tool · Freemium
LangChain's platform for tracing, evaluating and monitoring LLM apps, with a prompt hub and playground.
Open source · MIT
CLI and library for testing LLM prompts and red-teaming AI apps, with declarative configs.
The short answer
Choose LangSmith if you need…
- LangChain and LangGraph users
- Dataset-based evaluation
Choose promptfoo if you need…
- Developers building apps on top of LLM APIs who want repeatable prompt tests
- Teams comparing several models side by side on the same prompts
- People who want to run automated LLM checks in CI/CD pipelines
- Teams looking for a local, command-line way to scan LLM apps for security issues
Side-by-side
| LangSmith | promptfoo | |
|---|---|---|
| Type | Prompting · Evaluation & observability | Dev tool |
| Price | Freemium | Free and open source |
| Licence | — | MIT |
| GitHub stars | — | 26.7k |
| Setup difficulty | — | Intermediate |
| How you get it | — | Install with a package manager |
| Platforms | Web, API | CLI, Web |
| Works with | LangChain, OpenAI | GitHub, OpenAI, Anthropic |
| Main language | — | TypeScript |
| Last code update | — | 4 days ago |
| Hands-on tested by us | Not yet | — |
| Last checked | 2026-10-29 | — |
What each one is
LangSmith
LangChain's platform for tracing, evaluating and monitoring LLM apps, with a prompt hub and playground. Deep tooling, especially inside the LangChain ecosystem. Less compelling if you don't use LangChain.
promptfoo
Promptfoo is a command-line tool and library for evaluating LLM-based apps. You write a declarative config listing prompts, models, and test cases, then run it to compare outputs across providers such as OpenAI, Anthropic, and Ollama. It also includes red-teaming features that scan AI apps for security vulnerabilities.
Best for
LangSmith
- LangChain and LangGraph users
- Dataset-based evaluation
promptfoo
- Developers building apps on top of LLM APIs who want repeatable prompt tests
- Teams comparing several models side by side on the same prompts
- People who want to run automated LLM checks in CI/CD pipelines
- Teams looking for a local, command-line way to scan LLM apps for security issues
Strengths
LangSmith
- Detailed run traces
- Datasets and evaluators
- Prompt hub and playground
- Production monitoring
promptfoo
- The README states that evals run locally and prompts never leave your machine
- Works with many providers and any LLM API, according to the README
- Has a large community with about 26,500 stars and an MIT license
Not ideal for
LangSmith
—
promptfoo
- People who want a no-code, point-and-click tool, since the workflow centers on the command line and config files
- Projects that do not call any LLM APIs, because there is nothing for it to evaluate
- Anyone who needs a guaranteed security audit, since the README describes scanning as a tool rather than a complete assurance
Trade-offs
LangSmith
—
promptfoo
- The README says the project is now part of OpenAI, which may matter to some users evaluating independence
- Requires API keys for most providers, which means usage costs from those providers
- Some claims in the README, such as usage by OpenAI and Anthropic and serving 10M+ users, are not independently verified here
Getting started
LangSmith
Get started on the LangSmith websitepromptfoo
Install globally with npm
npm install -g promptfooCreate a starter example
promptfoo init --example getting-startedFrequently asked questions
What is the difference between LangSmith and promptfoo?
LangSmith: LangChain's platform for tracing, evaluating and monitoring LLM apps, with a prompt hub and playground. promptfoo: CLI and library for testing LLM prompts and red-teaming AI apps, with declarative configs. LangSmith suits langchain and langgraph users, while promptfoo suits developers building apps on top of llm apis who want repeatable prompt tests.
Are LangSmith and promptfoo free?
LangSmith: Freemium. promptfoo: Free and open source.
What are other alternatives to LangSmith and promptfoo?
Other options people compare them with include Langfuse, Arize Phoenix, Opik, Braintrust, Confident AI (DeepEval).
Keep comparing
Built from our catalogue entries for both products: open-source details come from each project's README (AI-assisted, refreshed weekly) and GitHub data; AI-tool details are editorial. Spotted something wrong? Let us know from either product's page.