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21st Agents SDK

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The fastest way to integrate AI agents with built-in UI and essential features into your applications.

Developer ToolsAI AgentsUI/UX Design
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Tracked since2026
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The Bottom Line

Entry price

Free plan available, paid tiers above

Biggest pro

Accelerates AI agent integration

TL;DR - 21st Agents SDK

  • Quickly integrate AI agents into applications.
  • Includes built-in UI, chat history, and spend limits.
  • Supports tool execution, memory, and observability.
Pricing: Free plan available
Best for: Growing teams

What is 21st Agents SDK?

Editorial review
The 21st Agents SDK is a software development kit designed to simplify the process of adding AI agents to web applications. It provides developers with pre-built components and functionalities to quickly integrate AI agents, including a built-in user interface for interaction, chat history management, and mechanisms for controlling AI spend. The SDK also supports tool execution, allowing AI agents to interact with external services, and incorporates memory capabilities for more contextual conversations. Furthermore, it offers observability features to monitor agent performance and behavior. This SDK is ideal for developers and teams looking to enhance their applications with intelligent AI capabilities without building agent infrastructure from scratch. It's particularly useful for those working with modern web frameworks and technologies like Next.js, React, TypeScript, Python, and Node.js, and integrates well with platforms like OpenAI and Vercel. The key benefit is accelerating development time for AI-powered features, providing a comprehensive solution that handles many common challenges associated with AI agent deployment.

Available on: Web

how we evaluateSource21st.dev ↗

Pros & Cons

Pros

  • Accelerates AI agent integration
  • Provides essential features out-of-the-box
  • Compatible with popular web technologies
  • Handles complex aspects like memory and tool use

Preview

Key Features

Built-in UI for AI agentsChat history managementSpend limits for AI usageTool execution capabilitiesMemory for contextual conversationsObservability features

Pricing Plans

Pricing checked Aug 30, 2026

Builder

$6/month

  • $6/month billed yearly
  • Unlimited copies, MCP installs, icons
  • No monthly AI credits

Builder + AI

$15/month

  • $15/month billed yearly
  • 500, 1,000, or 2,000 AI credits/month
  • Multi-model sketch, code mode

Team

$7.5/month

  • $7.50 per seat/month billed yearly
  • 2–50 seats
  • Optional AI credits per seat

Extra AI credits

$5 / 100 credits

  • +100 for $5
  • Rolls over
  • Builder + AI and Team + AI
Calculate your costView full pricing

Is 21st Agents SDK worth the price?

73/100

21st.dev publishes yearly list prices: Builder $6/month, Builder + AI $15/month, Team $7.50/seat/month (2–50 seats).

Yearly is advertised as 25% off. Marketplace copy and MCP are unlimited on Builder.

AI credits start on Builder + AI (500 to 2,000). Extra packs are $5 per 100 and they roll over.

Payments are non-refundable. Cancel anytime.

This is best for a solo who only needs MCP copy at $6, or who will actually burn 500+ credits at $15.

Hidden Costs & Gotchas

These $ are billed yearly. The page says save 25% vs quarterly.

Extra credits $5/100. They roll over. Plan credits are monthly.

Team AI is optional per seat. $7.50 is marketplace + admin, not 2,000 credits.

How 21st Agents SDK's pricing compares

At $5/mo, 21st Agents SDK is the most affordable of its 4 direct competitors.

21st Agents SDK
$5
Convai
$5
Firecrawl MCP
$16
LangChain
$39
Devin
$500

Entry paid plan, monthly. Pricing checked Aug 30, 2026.

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Still deciding?

Most buyers shortlist 2 or 3 tools before committing. Pull a side-by-side comparison or browse the full alternatives shortlist below.

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21st Agents SDK FAQ

How does the 21st Agents SDK accelerate the integration of AI agents into applications?

The 21st Agents SDK provides pre-built components and functionalities, including a built-in user interface, to simplify adding AI agents to web applications. This allows developers to quickly integrate intelligent AI capabilities without building the agent infrastructure from scratch.

Which teams would benefit most from using the 21st Agents SDK?

The 21st Agents SDK is ideal for developers and teams looking to enhance their applications with intelligent AI capabilities. It is particularly useful for those working with modern web frameworks and technologies such as Next.js, React, TypeScript, Python, and Node.js.

How does the 21st Agents SDK compare to LangChain regarding AI agent development?

The 21st Agents SDK focuses on providing a comprehensive solution with pre-built UI and essential features to accelerate AI agent integration into web applications. It handles complex aspects like memory and tool use, offering a streamlined approach for developers.

What kind of limitations or trade-offs should users consider when adopting the 21st Agents SDK?

The 21st Agents SDK is a paid product and does not include a permanently free tier, which means users will need to account for costs from the outset. While it accelerates integration, it is a specialized SDK focused on AI agents for web applications.

Can the 21st Agents SDK manage chat history and control AI spending?

Yes, the 21st Agents SDK includes built-in functionalities for managing chat history, ensuring contextual conversations. It also provides mechanisms designed to help control AI spend, offering developers better oversight of resource utilization.

How is the 21st Agents SDK priced?

The 21st Agents SDK is offered as a paid product. It does not include a permanently free tier, meaning users will need to subscribe to access its features and functionalities.

Does the 21st Agents SDK support interaction with external services?

Yes, the 21st Agents SDK supports tool execution, which enables AI agents to interact with external services. This allows agents to perform actions beyond their internal capabilities by leveraging other applications or platforms.

Source: 21st.dev

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