LangSmith
LangSmith is a platform for building, evaluating, deploying, monitoring, and improving AI agents.
What LangSmith is
LangSmith is a platform for building, evaluating, deploying, monitoring, and improving AI agents. It supports offline checks on curated datasets and real-time evaluation of production interactions. Teams can use human review, heuristic rules, model-based judges, pairwise comparisons, or custom evaluators in Python and TypeScript. Annotation queues route runs to subject-matter experts, whose feedback can help calibrate evaluations, refine prompts, or expand datasets. The Playground lets users experiment with prompts and compare outputs across versions or model providers; LangSmith chat can also improve prompts. Observability features include agent traces, cost tracking, trajectory monitoring, online evaluations, and webhook or PagerDuty alerts. It accepts traces through an SDK or API from LangGraph, custom Python, and other stacks, and supports evaluation workflows with pytest, Vitest, and GitHub. Cloud plans start with a free Developer tier; Plus costs $39/user/mo. Enterprise hosting options include cloud, hybrid, and self-hosted deployment.
Good
- Offline and real-time evaluation options
- Custom evaluators in Python or TypeScript
- Tracks costs, traces, and agent trajectories
- Free Developer plan available
- Multiple hosting options for Enterprise
Watch out
- Base traces retain data for 14 days
- Extended trace retention costs extra
- Plus is $39/user/mo
Who it suits
LangSmith suits teams building or operating AI agents that need evaluation, prompt workflows, and observability. It supports both hosted and self-hosted deployment options.
Verdict
LangSmith brings agent evaluation, prompt work, and production monitoring into one platform. The free Developer tier offers an entry point, while paid plans add higher trace allowances and additional capabilities.
Plans and prices
From LangSmith's own pricing page, checked 15 Oct 2026.
| Plan | Price | What it gives you |
|---|---|---|
| Developer | Free | 1 seat · 5,000 base traces/month · community support · $0 per seat per month; usage pay-as-you-go |
| Plus | $39 a month | 10,000 base traces/month · unlimited seats · 1 free small serverless deployment · $39 per seat per month; usage pay-as-you-go |
| Enterprise | Priced on request | self-hosted or hybrid deployment · custom SSO, ABAC and RBAC · support SLA · invoiced annually upfront; usage pay-as-you-go |
The facts
Each one read from LangSmith's own pages, with the date it was checked.
What it does
- API and CLI
- LangSmith exposes a REST API and a CLI that manages projects, traces, runs, datasets, evaluators, experiments, threads and sandboxes.checked 15 Oct 2026
- CI/CD
- The evaluation workflow integrates with pytest, Vitest and GitHub workflows for automated regression checks.checked 15 Oct 2026
- CLI installation
- The CLI provides installation paths for macOS, Linux and Windows through shell scripts, PowerShell, Homebrew, Scoop, Go or downloadable binaries.checked 15 Oct 2026
- Data residency
- Cloud data is hosted in GCP US or EU regions, while self-hosted data remains in the customer's VPC.checked 15 Oct 2026
- Data use
- LangChain states that LangSmith data is not used to train models and remains owned by the customer.checked 15 Oct 2026
- Deployment
- Deployment provides managed or self-hosted agent servers with streaming, cron scheduling, authentication, MCP support and more than 30 API endpoints.checked 15 Oct 2026
- Documentation
- LangChain publishes reference documentation, integration guides, deployment instructions, a CLI guide and a REST API reference.checked 15 Oct 2026
- Evaluation
- Evaluation supports offline datasets, online production evaluations, human annotation queues and side-by-side experiment comparison.checked 15 Oct 2026
- Evaluators
- Its evaluation framework supports human review, heuristic checks, LLM-as-judge evaluators, pairwise comparisons, and custom evaluators in Python or TypeScript.checked 5 Oct 2026
- Evaluator types
- Evaluators can be human, heuristic, LLM-as-judge, pairwise or custom Python and TypeScript code.checked 15 Oct 2026
- Framework support
- LangSmith is framework-agnostic and accepts traces through its SDK or API from LangGraph, custom Python, or other application stacks.checked 5 Oct 2026
- Funding
- LangChain announced a $125 million Series B at a $1.25 billion valuation on October 20, 2025.checked 15 Oct 2026
- Hosting
- The pricing page lists Cloud hosting for Developer and Plus, with Cloud, Hybrid, or Self-Hosted options for Enterprise.checked 5 Oct 2026
- Human feedback
- Annotation queues let teams assign runs to subject-matter experts and use feedback to calibrate evaluations, improve prompts, or augment datasets.checked 5 Oct 2026
- Integrations
- Documented integrations cover OpenAI, Anthropic, Bedrock, Gemini, Mistral, LiteLLM, OpenTelemetry, CrewAI, Vercel AI SDK, PydanticAI, AutoGen and many other frameworks and providers.checked 15 Oct 2026
- Legal entity
- Crunchbase identifies the maker as LangChain, Inc., a privately held San Francisco company founded by Harrison Chase and Ankush Gola.checked 15 Oct 2026
- Limit: deployment documentation
- A LangChain forum user reported authentication failures and difficulty understanding deployment secrets, assistant IDs and setup documentation.checked 15 Oct 2026
- Limit: large datasets
- Product Hunt reviewers report that the UI becomes cumbersome with large datasets and long experiment histories, and filtered-result sharing is awkward.checked 15 Oct 2026
- Limit: learning curve
- Reviewers commonly describe the interface and concepts as dense or overwhelming for new users.checked 15 Oct 2026
- Limit: outage
- On May 1, 2025, a certificate and DNS configuration error caused a 28-minute US API, web and SDK outage with about 55% of requests failing.checked 15 Oct 2026
The company
- Company origins
- LangChain says the company began in early 2023 and that LangSmith launched first as a commercial observability product before expanding into evaluation and deployment.checked 15 Oct 2026
- Company profile
- LinkedIn lists LangChain as privately held, headquartered in San Francisco, with 201–500 employees and 469 employees shown on the page.checked 15 Oct 2026
- Founded
- 2023checked 28 Sep 2026
- Headquarters
- San Francisco, California, United Stateschecked 28 Sep 2026
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