21st Agents SDK
Accelerate AI-powered product development with open-source tools and managed infrastructure.
VS
LangSmith
AI Agent & LLM Observability Platform
Detailed comparison
Criteria
21st Agents SDK
LangSmith
Pricing
Freemium
Freemium
Plans & pricing
—
Developer: Free, Team: $39/mo, Enterprise: Custom
Free trial
—
No
Audience
B2B
b2b
Platforms
—
Web
API
—
Yes
Open Source
—
Proprietary
Integrations
—
Pagerduty
Categories
Dev & Tech, AI & ML
Dev & Tech, information technology & services, Apps
Popularity
Moderate
Very High
Description
The 21st Agents SDK provides open-source UI components and developer tools for building and deploying AI agents faster. It's designed for frontend eng...
LangSmith is a complete AI agent and LLM observability platform. It offers tracing and real-time monitoring to help developers debug agents, find fail...
Pricing
21st Agents SDK
Freemium
LangSmith
Freemium
Plans & pricing
21st Agents SDK
—
LangSmith
Developer: Free, Team: $39/mo, Enterprise: Custom
Free trial
21st Agents SDK
—
LangSmith
No
Audience
21st Agents SDK
B2B
LangSmith
b2b
Platforms
21st Agents SDK
—
LangSmith
Web
API
21st Agents SDK
—
LangSmith
Yes
Open Source
21st Agents SDK
—
LangSmith
Proprietary
Integrations
21st Agents SDK
—
LangSmith
Pagerduty
Categories
21st Agents SDK
Dev & Tech, AI & ML
LangSmith
Dev & Tech, information technology & services, Apps
Popularity
21st Agents SDK
Moderate
LangSmith
Very High
Description
21st Agents SDK
The 21st Agents SDK provides open-source UI components and developer tools for building and deploying AI agents faster. It's designed for frontend eng...
LangSmith
LangSmith is a complete AI agent and LLM observability platform. It offers tracing and real-time monitoring to help developers debug agents, find fail...
Features
21st Agents SDK
Built-in UI and chat history
Spend limits and sandbox execution with isolated VMs
Observability including session replay and traces
Supports Claude and OpenAI models with token-by-token streaming
LangSmith
Cost tracking
Online LLM-as-judge and code evals
Tool and agent trajectory monitoring
Webhook and Pagerduty alerts
Message threading for multi-turn chat interactions
Templates for error analysis
Key differentiators
21st Agents SDK
LangSmith
- Complete AI agent & LLM observability
- Real-time tracing, debugging & evals
- Cost, latency & trajectory monitoring
Other comparisons
FAQ: 21st Agents SDK vs LangSmith
21st Agents SDK: Accelerate AI-powered product development with open-source tools and managed infrastructure.. LangSmith: AI Agent & LLM Observability Platform. Both tools take different approaches to address similar needs.
Both offer a free or freemium plan. 21st Agents SDK is freemium and LangSmith is freemium.
The best choice between 21st Agents SDK and LangSmith depends on your specific needs. Compare their features, pricing, and target audience on this page to find the tool that best fits your use case.
21st Agents SDK is primarily designed for businesses and professionals, while LangSmith is built for individuals.
21st Agents SDK offers: Built-in UI and chat history, Spend limits and sandbox execution with isolated VMs, Observability including session replay and traces, Supports Claude and OpenAI models with token-by-token streaming. LangSmith offers: Cost tracking, Online LLM-as-judge and code evals, Tool and agent trajectory monitoring, Webhook and Pagerduty alerts.
Based on our data, LangSmith currently enjoys greater popularity. However, popularity isn't the only factor — compare features to find the right tool for your needs.